(19)
(11)EP 3 568 199 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
01.12.2021 Bulletin 2021/48

(21)Application number: 18738677.6

(22)Date of filing:  08.03.2018
(51)International Patent Classification (IPC): 
A61N 5/00(2006.01)
A61N 5/10(2006.01)
(52)Cooperative Patent Classification (CPC):
A61N 2005/1087; A61N 5/1037; A61N 5/1044; A61N 5/1043; A61N 5/00; A61N 5/1068
(86)International application number:
PCT/US2018/021475
(87)International publication number:
WO 2018/132847 (19.07.2018 Gazette  2018/29)

(54)

MITIGATION OF INTERPLAY EFFECT IN PARTICLE RADIATION THERAPY

ABSCHWÄCHUNG DES ZUSAMMENWIRKEFFEKTES BEI DER TEILCHENSTRAHLENTHERAPIE

ATTÉNUATION DE L'EFFET D'INTERACTIONS DANS UNE THÉRAPIE PAR RAYONNEMENT DE PARTICULES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME

(30)Priority: 11.01.2017 US 201762445008 P

(43)Date of publication of application:
20.11.2019 Bulletin 2019/47

(73)Proprietors:
  • Varian Medical Systems Particle Therapy GmbH & Co. KG
    53842 Troisdorf (DE)
  • University of Maryland, Baltimore
    Baltimore, MD 21201 (US)

(72)Inventors:
  • POULSEN, Per, Rugaard
    8230 Abyhoj (DK)
  • ELEY, John
    Baltimore MD 21212 (US)
  • LANGNER, Ulrich
    Ellicott City MD 21042 (US)
  • LANGEN, Katja
    Baltimore MD 21231 (US)

(74)Representative: Foster, Mark Charles et al
Mathisen & Macara LLP Communications House South Street
Staines-upon-Thames, Middlesex TW18 4PR
Staines-upon-Thames, Middlesex TW18 4PR (GB)


(56)References cited: : 
US-A1- 2013 303 899
US-A1- 2014 031 602
US-A1- 2016 030 769
US-A1- 2013 303 899
US-A1- 2014 031 602
US-A1- 2016 030 769
  
  • XP055511640
  • TSUNASHIMA Y.: 'Verification of the clinical implementation of the respiratory gated beam delivery technique with synchrotron-based proton irradiation' TEXAS MEDICAL CENTER LIBRARY May 2012, pages 1 - 226, XP055511640
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

FIELD



[0001] The invention relates to scan techniques to mitigate interplay effect in delivery of particle radiation to a treatment target in motion.

BACKGROUND



[0002] Particle radiation therapy (also called hadron therapy) is a form of external beam radiotherapy that uses beam(s) of energetic protons, ions, electrons, or electrons for treatment of cancer or other diseases. Further, pencil beam scanning (PBS) therapy is a type of particle radiation therapy that often allows excellent three-dimensional (3D) shaping of a high-dose radiation volume to a shape of a treatment target such as a tumor. With particle PBS therapy, the radiation treatment is delivered in several layers (beam energies or energy layers), where a pencil beam of energized particles is scanned to cover a cross section of the treatment target at specific energy-dependent depths.

[0003] However, during particle PBS therapy delivery, treatment target motion (e.g., tumor motion), for example, due to breathing or the heartbeat, will change the relative positions of treatment target volumes or spots that are irradiated sequentially by the scanning pencil beam. The size of the treatment target volumes or spots depends on a width of the pencil beam of energized particles. The resulting redistribution of dose in the treatment target tissue is called the interplay effect, and it can lead to severe local underdosage and/or overdosage inside the treatment target volume. This is a major concern for particle PBS therapy in the thorax and abdomen, in particular for stereotactic body radiotherapy (SBRT), where high doses are delivered in few fractions. Besides the interplay effect, treatment target motion (e.g., tumor motion) also shifts and smears the delivered target dose, but this smearing effect is common for particle PBS therapy and other treatment techniques, such as conventional photon radiotherapy and passively scattered particle beams. Unlike other motioninduced dose perturbations that impact the dose at the treatment target edge (e.g., dose blurring due to random position errors and dose shifts due to systematic position errors), the interplay effect typically cannot be accounted for by a simple expansion of the high-dose radiation volume with safety margins.

[0004] Although the interplay effect may tend to average out after several treatment deliveries because the hot spot and cold spot locations typically differ randomly between each treatment delivery, the interplay effect is more serious for treatments delivered in few fractions because the dose smearing effect of many fractions is absent. Since SBRT is delivered in few fractions, SBRT is susceptible to pronounced interplay effect in moving target organs, such as lung, liver, or pancreas. Consequently, many particle radiation therapy centers do not offer SBRT treatments at all. Even for normal-fractionated treatments, many particle radiation therapy centers only treat highly selected tumors with minor motion due to respiratory motion.

[0005] US2016/0030769A1 describes a method and device designed to deliver intensity-modulated ion beam therapy radiation doses closely conforming to tumors of arbitrary shape, via a series of two-dimensional (2-D) continuous raster scans of a pencil beam, wherein each scan takes no more than about 100 milliseconds to complete. The device includes a fast scanning nozzle for the exit of an ion beam delivery gantry. The fast scanning nozzle has a fast combined-function X-Y steering magnet, and is coupled to a rastering control system capable of adjusting the length of each scan line, continuously varying the beam intensity along each scan line, and executing multiple rescans of a tumor depth layer within a single patient breathing cycle. An in-beam absolute dose and dose profile monitoring system is capable of millimeter-scale position resolution and millisecond-scale feedback to the control system to ensure the safety and efficacy of the treatment implementation.

SUMMARY



[0006] The invention is as defined in the appended claims. Embodiments, examples or aspects in the following disclosure, which do not fall under the scope of the claims, in particular methods of treatment, are presented for illustration purposes only and do not form part of the invention.

[0007] A new scan technique that integrates repainting for particle radiation therapy to efficiently reduce interplay effects is disclosed. The new scan technique is suitable for mitigating interplay effects in particle radiation therapy delivered to a moving treatment target, such as a tumor. In embodiments, the motion of the moving treatment target is periodic and has a period, where the period may be determined in any manner, such as experimental, empirical, or calculation methods. Moreover, the motion may be due to respiration, heartbeat, or other motion source.

[0008] In cross-sectional layers of the treatment target, a spot or region is irradiated with the particle radiation according to the new scan technique. A particle radiation treatment plan typically defines a planned dose at each spot of each layer of the treatment target. A shape of the spot may be any of numerous shapes, may have multiple-dimensions (e.g., two-dimensional 2D or three-dimensional 3D), and may have a volume. Continuing, the spot may have a wait time that corresponds to time between beam-on times at the spot and a beam-on time that corresponds to time during which the beam of particle radiation irradiates the spot. Additionally, the wait time may correspond to time before a first beam irradiates the spot. The new scan technique focuses on optimizing the wait time to achieve reduction in the interplay effect. In contrast, conventional methods of addressing the interplay effect optimize the beam-on time.

[0009] According to embodiments, a planned dose for a spot of a layer is divided into a number of spot repaintings. Similar action is performed for the rest of the spots of the layer. Also, a scan pattern for each layer is generated by defining a beam-on time at each spot for each spot repainting and calculating a wait time between consecutive beam-on times at each spot. The wait time is calculated such that the spot repaintings for each spot of the layer are distributed over an integer number of periods of movement of the moving treatment target. In an embodiment, the spot repaintings are distributed evenly within the integer number of periods. The treatment delivery at each spot may be defined by the waiting time (for layer shift or spot position shift) followed by the beam-on time. Moreover, the scan pattern generation may be seen as determining an order of the spot repaintings. In an example, the period of movement may be the breathing period/cycle of a patient under radiation treatment. The breathing period is typically quite stable. Additionally, the period of movement also may be an approximate period of an approximately periodic movement.

[0010] Accordingly, the interplay effect in each individual layer (or energy layer) may be smeared out by tuning a duration of layer treatment delivery to one or more periods of movement. Further, the dose delivered to each spot in the layer may be delivered in equal portions with equal temporal separations over duration of the period of movement. This ensures that the mean shift of each spot relative to its planned position is close to zero, which in turn gives a large reduction of the interplay effect. Also, it possible to use a different number of repaintings for each spot, but still spread out the spot repaintings throughout the period of movement.

[0011] Therefore, the new scan technique spreads the treatment delivery of each energy layer over the period of movement (e.g., a breathing cycle), allows spot-specific numbers of spot repaintings, and ensures that the spot repaintings are spread over the duration of the movement period. Mitigation of the interplay effect in particle radiation therapy by using the new scan technique is superior to conventional methods of mitigating the interplay effect. Moreover, the new scan technique allows safe PBS treatments of tumors undergoing respiratory motion in the thorax or abdomen, including SBRT treatments delivered in very few fractions. In an embodiment, no monitoring of the patient's breathing or synchronization of the treatment delivery to the breathing phase is needed. Further, the new scan technique may be immediately implemented at existing particle radiation therapy centers such as cyclotron-based proton radiation therapy facilities without any requirements of intra-treatment motion monitoring, gating, or synchronization between patient breathing and treatment delivery. In an embodiment, the new scan technique involves configuring the spot treatment delivery sequence in a Digital Imaging and Communications in Medicine (DICOM) proton radiation treatment plan.

BRIEF DESCRIPTION OF THE DRAWINGS



[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments, together with the description, serve to explain the principles of the disclosure.

Figure 1A illustrates three dose distributions with proton PBS to liver tumors.

Figure 1B depicts a dose-volume histogram for the liver tumors of Figure 1A.

Figure 2A shows a timing graph of treatment delivery to a spot in a layer according to an embodiment.

Figure 2B illustrates equations for waiting time twait, beam-on time tbeam-on, and tmin related to a spot according to an embodiment.

Figure 3 depicts a comparison graph of actual times with predicted times from equations (1)-(3) according to an embodiment.

Figure 4 shows scatter plots of actual and predicted values of twait and tbeam-on according to an embodiment.

Figure 5 depicts a graph of maximum and planned waiting times twait and beam-on times tbeam-on of spots in a layer according to an embodiment.

Figure 6 illustrates spots sorted into repainting blocks according to an embodiment.

Figure 7 shows a table with eight scan modes in order of increasingly slower scan duration according to an embodiment.

Figure 8 depicts obtaining the treatment delivery time of a layer with a duration of 4s (the period T = 4s of the breathing cycle) according to an embodiment.

Figure 9 illustrates repainting blocks rearranged according to an embodiment.

Figure 10 shows new scan technique with repainting scheme for a special case according to an embodiment.

Figure 11 shows a graph with examples of the treatment delivery durations of layers for one field with a planned treatment delivery without use of the new scan technique.

Figure 12 illustrates a graph with examples of the treatment delivery durations of layers for one field with treatment delivery according Figures 9 (method 1) and 10 (method 2) according to an embodiment.

Figure 13 depicts a graph that demonstrates actual treatment delivery times are reasonably close to predicted treatment delivery times with equations (1)-(3) of Figure 2B according to an embodiment.

Figure 14 illustrates a set-up to investigate the new scan technique according to an embodiment.

Figure 15 shows a block diagram for performing a gamma test according to an embodiment.

Figure 16 depicts examples of measured doses with an ion chamber array for a patient under treatment according to an embodiment.

Figure 17 illustrates the results for 3 x 24 motion experiments according to an embodiment.

Figure 18 shows a block diagram for a gamma test according to an embodiment.

Figure 19 depicts a block diagram to reproduce experimental gamma pass rates for the interplay effect according to an embodiment.

Figure 20 illustrates a graph of gamma pass rates according to an embodiment.

Figure 21 shows a graph for investigating the impact of motion amplitude according to an embodiment.

Figure 22 shows a graph for investigating the impact of a breathing period differing from period T = 4s according to an embodiment.

Figure 23 shows a graph for investigating the smearing of the interplay effect with fractionated delivery according to an embodiment.

Figure 24 depicts a graph for investigating the interplay effect for the actually measured tumor motion as measured for six liver SBRT patients during treatment delivery with kilovoltage intrafraction imaging (KIM) according to an embodiment.

Figure 25 illustrates three dose distributions according to an embodiment.

Figure 26 shows a dose-volume histogram for internal clinical target volume (ICTV) of 4D dose reconstruction according to an embodiment.


DETAILED DESCRIPTION



[0013] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. While the disclosure will be described in conjunction with these embodiments, it should be understood that they are not intended to limit the disclosure to these embodiments. On the contrary, the disclosure is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the disclosure as defined by the appended claims. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding. However, it will be recognized by one of ordinary skill in the art that embodiments may be practiced without these specific details.

[0014] Although the description will focus on proton radiation therapy and proton pencil beam scanning (PBS) therapy, the description is also applicable to particle radiation therapy that uses neutrons, ions, or electrons. The proton radiation therapy may irradiate a treatment target of a patient. The treatment target may comprise a tumor, diseased tissue, or at least part thereof. In embodiments, a motion of the treatment target is periodic and has a period. For example, the motion may be due to a periodic movement of a breathing cycle or a heartbeat. Alternatively, the motion of the treatment target may be approximately periodic and may have an approximate period. The period of movement such as the breathing period and/or heartbeat movement may be obtained from a 4D Computed Tomography scan (4DCT), which may be performed for radiation treatment planning. In an embodiment, auditory and/or visual guidance may be utilized during treatment delivery to assist the patient to breathe with the period duration (or the frequency) recorded during the 4DCT scan session.

[0015] Continuing, a dose delivered to a spot has a value that is at least a predefined minimum dose dependent on particle radiation therapy equipment delivering the dose. In order to mitigate the interplay effect, the number of spot repaintings at each spot is maximized or optimized according to the predefined minimum dose (or minimum spot dose) of the particle radiation therapy. The spot repaintings of each spot of a layer may then be distributed over an integer number of periods of movement. In an embodiment, the spot repaintings are distributed evenly over the duration of the integer number of periods. Because the particle radiation therapy equipment typically is limited to the predefined minimum dose, some spots of the treatment target will be irradiated once instead of being irradiated multiple times. According to the new scan technique, a scan pattern may then be generated such that spots in a layer that are irradiated once are distributed in a manner in which one set of these spots is irradiated during a first part of the period of the periodic motion and the other set of these spots is irradiated during a second part of the period of the periodic motion.

[0016] In embodiments, layers with a maximum scan time less than the period of the periodic motion may be scanned using a scan pattern with a maximum scan time. Also, spot repaintings in a scan pattern for a layer may be distributed by adjusting a sequence order of spots and/or spot repaintings in the layer and/or by adjusting the wait time between consecutive beam-on times of spots in the layer. In some particle radiation therapy facilities, it is not possible to pause the beam of energized particles with 100% controllability. The new scan technique avoids this problem by focusing on adjusting the wait time of spots, the sequence of spot repaintings, and the number of spot repaintings to distribute the radiation delivery of the therapy. But, it may be an option to be able to pause the beam of energized particles in some particle radiation therapy facilities. In further embodiments, the wait time between consecutive beam-on times of a spot in a layer may therefore be adjusted by selecting a beam pause before one or more spots in a scan pattern.

[0017] The number of spot repaintings for each spot of a layer may be decomposed into repainting blocks or groups, where the number of spot repaintings in each repainting block (or group) may be an integer power of two, in an embodiment. Accordingly, the spot repaintings of each repainting block may be distributed over an integer number of periods of movement in an embodiment. The spot repaintings may be distributed evenly over the duration of the integer number of periods of movement. Also, synchronization of a patient's breathing and a determined respiratory period of movement may be assisted by means of audio and/or visual guidance.

[0018] Continuing, in cases where the scan time for a layer is two periods, the scan pattern may be generated such that repainting blocks of two or more spot repaintings are separated into two identical scan patterns, where a first scan pattern is performed in the first period of two periods and a second scan pattern is performed in the second period of two periods. Alternatively, the scan pattern may be generated such that repainting blocks of two or more spot repaintings are separated into two scan patterns, where a first scan pattern is performed in a first period of two periods and a second scan is performed in a second period of two periods, the second scan pattern being the reverse of the first scan pattern.

Modeling of Proton PBS Timing



[0019] An ideal dose distribution to a moving tumor without interplay effects (although with smearing) would be the planned dose to the static tumor smeared or convolved with the tumor motion. This may to some degree be obtained by repainting (or rescanning), where the beam of energized particles is scanned several times over spots of a treatment target to smear out the interplay effect. The beam of energized particles may be scanned N times over spots of the treatment target (N = 2, 3, 4,), each time delivering 1/N of the planned dose (or monitor units) to each spot. The number of monitor units (MU) cannot be smaller than a minimum limit MUmin. A typical clinical proton PBS treatment plan may have many spots with too few MUs to allow any repainting at all. Further, conventional methods of reducing the interplay effect are inefficient. They do not guarantee elimination of the interplay effect. Also, they are often not practically applicable because of proton radiation therapy equipment limitations imposed by proton accelerators and their beams of energized protons.

[0020] The new scan technique is superior to conventional strategies for mitigating the interplay effect in proton PBS therapy according to experiments, simulations, and dose reconstructions, as will be described next. In the discussion below, motion of the treatment target is due to periodic respiratory movement with a breathing period T = 4s. It should be understood that the discussion is equally applicable to other types of periodic movement and to other values for the period.

[0021] Figure 1A illustrates three dose distributions with proton PBS to liver tumors. Dose distribution 2 shows a planned uniform dose distribution with proton PBS to a motionless liver tumor. Dose distribution 4 depicts delivered doses in simulated treatments without repainting (1 painting or spots painted once) with proton PBS to a moving liver tumor. Further, dose distribution 6 depicts delivered doses in simulated treatments with 10× repainting (spots painted 10 times) with proton PBS to a moving liver tumor.

[0022] The interplay effect between liver tumor motion and the scanning proton beam leads to severe underdoses/overdoses 9 in the dose distribution 4. This interplay effect is to some degree smeared out by the 10 repaintings in the dose distribution 6 to cause a reduction in underdoses/overdoses 9, but it is still a problem.

[0023] Figure 1B depicts a dose-volume histogram 10 for the liver tumors of Figure 1A. The dose-volume histogram 10 points out the underdoses/overdoses 9 in the dose distributions 4 and 6.

[0024] As mentioned above, motion of the treatment target is due to periodic respiratory movement with a breathing period T = 4s. It should be understood that the discussion is equally applicable to other types of periodic movement and to other values for the period.

[0025] For the new scan technique, modeling of the timing of treatment delivery to spots of a layer permits adjustment of duration of treatment deliver to the layer to be an integer number of periods, where the period T = 4s for this discussion.

[0026] Continuing, Figure 2A shows a timing graph 12 of treatment delivery to a spot in a layer according to an embodiment. According to the timing graph 12, the spot has a waiting time twait 14 (for layer shift or spot position shift) followed by a beam-on time tbeam-on 16.

[0027] For proton PBS therapy equipment of a proton radiation therapy center, patient treatment log files may be analyzed to find an approximate value for the waiting time twait 14. Equation (1) of Figure 2B was derived from the patient treatment log files for the waiting time twait 14. The equation (1) for the waiting time twait 14 includes the following values: the spot delay constants t0,x = 2.85ms and t0,y = 3.52ms and spot speeds vx = 6.92mm/ms in the X-direction and vy = 32.1 mm/ms in the Y-direction. The threshold distance dthreshold between spots is 10mm. Also, the waiting time twait 14 depends on the distance (Δx and Δy) of the spot from the previous spot. The spot speeds vx and vy depend approximately linearly on the proton beam energy, but this is omitted in the modeling of the waiting time twait 14. Although the modeling of the waiting time twait 14 may be improved, it is found to be sufficiently accurate to demonstrate the advantages of the new scan technique to reduce the interplay effect.

[0028] Additionally, equation (2) of Figure 2B was derived from the patient treatment log files for the beam-on time tbeam-on 16. According to equation (2), the beam-on time tbeam-on 16 of a spot is proportional to the dose or number of monitor units (MU) delivered to the spot. Here, MUmin_layer is the minimum number of MUs in any spot in the layer, and tmin is the beam-on time for spots with MU = MUmin_layer, which corresponds to the shortest beam-on time in the layer. Also, Figure 2B's equation (3) for tmin represents approximate and empirically determined values for tmin.

[0029] Figure 3 depicts a comparison graph 18 of actual beam-on times tbeam-on and beam waiting times twait for 35 energy layers of a proton field with the beam-on times tbeam-on and beam waiting times twait as predicted from equations (1)-(3) according to an embodiment. The actual times are in agreement with the predicted times of equations (1)-(3), demonstrating the accuracy of equations (1)-(3). Further, Figure 4 shows scatter plots 20 and 22 of actual and predicted values of twait and tbeam-on for all energy layers in 13 investigated clinical treatment fields according to an embodiment. As shown in Figure 4, equations (1)-(3) in general give a reasonably accurate prediction of beam-on time tbeam-on and waiting time twait. Also, the root-mean-square error in the predicted times are 0.20s and 0.0026s for predicted beam-on time tbeam-on and waiting time twait, respectively.

New Scan Technique that Integrates Repainting



[0030] The new scan technique provides the ability to adjust the treatment delivery time of each energy layer to a period of movement (e.g., the breathing period of a patient). As mentioned above, the period of movement is assumed to be a breathing cycle of 4 seconds. It should be understood that the discussion is equally applicable to different types of periodic movement and different values for the period.

[0031] Conventional methods have tried to manipulate the treatment delivery time of a layer by adjusting the beam current, which is equivalent to adjusting the beam-on time tbeam-on. However, this strategy has very limited flexibility. It only allows modest prolongation of the treatment delivery time of the layer since most energy layers already are delivered with the lowest allowed beam current for the layer.

[0032] Instead, the new scan technique manipulates the time between each spot, which represents the waiting time twait 14 defined in Figure 2A. Figure 5 depicts a graph 24 of maximum and planned waiting times twait and beam-on times tbeam-on (or irradiation time) of spots in a layer according to an embodiment. As seen in Figure 5, the maximum waiting times twait of spots in the layer may be extended significantly more relative to the maximum beam-on times tbeam-on (or irradiation time) of spots of the layer. This allows extension of the treatment delivery duration of many energy layers to the period T = 4s or more. Further, the graph 24 shows time values for 35 energy layers. Maximum waiting times twait may be obtained by maximizing the waiting time between spots of the layer while maximum beam-on times tbeam-on may be obtained by decreasing beam current to its minimum.

[0033] The new scan technique ensures temporal equidistant repaintings of each spot of a layer throughout the period T = 4s of the breathing cycle in an embodiment. Implementation of the new scan technique is described next.

[0034] Initially, spots of a layer are sorted according to how many times the spots may be repainted. Specifically, the spots are sorted into repainting blocks (or groups) 30, 32, 34, 36, and 38 as illustrated in Figure 6 according to an embodiment. Depending on the number of MUs to be delivered of the spots, the layer's spots are sorted into repainting blocks 32, 34, 36, and 38 for the spots to be painted 2, 4, 8, and 16 times, respectively. MUmin is predefined and represents a minimum allowed number of MUs for a spot. Accordingly, spots with >=16 MUmin are put into 16-paint repainting blocks 38. Spots with >=8MUmin are put into 8-paint repainting blocks 36. Spots with >=4MUmin are put into 4-paint repainting blocks 34. Spots with >=2MUmin are put into 2-paint repainting blocks 32. Spots with <2MUmin are put into one of the 1-paint repainting blocks 30. Further, a spot may be placed in more than one of repainting blocks (or groups) 32, 34, 36, and 38. For example, a spot with 14MUmin will be placed in the 8-paint repainting blocks 36, the 4-paint repainting blocks 34, and the 2-paint repainting blocks 32 because 14 = 8 + 4 + 2.

[0035] Moreover, the two 2-paint repainting blocks 32 are identical. They include the same sequence of spots and MUs. Similarly, the four 4-paint repainting blocks 34 are identical while the eight 8-paint repainting blocks 36 are identical. Also, the sixteen 16-paint repainting blocks 38 are identical. Spots with <2MUmin monitor units may not be repainted. They are divided into 1-paint repainting blocks 30, where odd numbered or designated spots are sorted into block 1a and even numbered or designated spots are sorted into block 1b.

[0036] Thereafter, taking into account of the repainting of spots of a layer, a scan mode is selected from a set of scan modes (Figure 7) of different scan durations and implemented on the sorted spots (Figure 6) of the layer until a particular scan mode is found that slows down the scanning of the spots of the layer to provide the layer with a treatment delivery time of duration greater than the period T = 4s of the breathing cycle. Accordingly, the treatment delivery time of the layer is stepwise increased by going from a fastest scan mode to slower and slower scan modes until the treatment delivery time of the layer exceeds the period T = 4s of the breathing cycle.

[0037] Figure 7 shows a table 40 with eight scan modes in order of increasingly slower scan duration according to an embodiment. Each scan mode has a different scan path strategy. The scan duration increases with the number of the scan mode because the overall waiting time twait of the layer increases. The scan mode that increases the treatment delivery time of the layer to more than the period T = 4s of the breathing cycle is selected. Scan mode 7 allows any even number of repaintings. For example, a spot with 40 repaintings will be placed twice in the 16-paint repainting blocks 38 and will be placed once in the 8-paint repainting blocks 36 because 40 = 16 + 16 + 8.

[0038] Continuing with implementation of the new scan technique, thresholds for repainting are trimmed to obtain 4s (the period T = 4s of the breathing cycle) for the treatment delivery time of the layer. As discussed earlier, scan modes (Figure 7) were used to increase the treatment delivery duration of the layer to a value greater than the period T = 4s of the breathing cycle. By increasing some of the thresholds for spots with 4-paint, 8-paint, or 16-paint repaintings, the treatment delivery duration of the layer is shortened to the period T = 4s of the breathing cycle. For example, some of the spots that could be painted 8 times are instead painted 4 times, eliminating four waiting times twait. The threshold for 2 paintings remains at 2MUmin, which ensures that any spot that may be painted twice or more is painted at least twice. Figure 8 depicts obtaining the treatment delivery time of a layer with a duration of 4s (the period T = 4s of the breathing cycle) according to an embodiment.

[0039] Next, the repainting blocks (or groups) 30, 32, 34, 36, and 38 are rearranged as illustrated in Figure 9 according to an embodiment. The rearrangement provides the new scan technique with a quasi-periodic repainting scheme with a 0.5s repetition rate and temporally spread-out repaintings of the spots of a layer throughout the duration of the period T = 4s of the breathing cycle no matter if the spots are painted twice, 4 times, 8 times, or 16 times. In an embodiment, the repaintings of the spots of a layer are evenly distributed throughout the duration of the period T = 4s of the breathing cycle. The spots that may be painted once are divided into the repainting blocks 30, where block 1a includes odd spots and block 1b includes even spots. The spots in these repainting blocks 30 (e.g., the n'th spot in block 1a and the n'th spot in block 1b) will often be neighboring spots. The new scan technique with the quasi-periodic repainting scheme shown in Figure 9 ensures that these neighboring spots are visited with 2 seconds in between, which will tend to locally smear out the interplay effect even for these low-MU spots that may be painted once but not repainted.

[0040] Referring again to Figure 9, the 2-paint repainting blocks 32 are divided into four quarters (2.1, 2.2, 2,3, 2.4) that are visited with 2 seconds in between. The 4-paint repainting blocks 34 are divided into two halves (4.1, 4.2) that are visited with 1 second in between. The 1-paint repainting blocks 30 are divided into quarters (1.a1, 1.a2, 1.a3, 1.a4, 1.b1, 1.b2, 1.b3, 1.b4), where neighboring odd and even spots are visited with 2 seconds in between.

[0041] Some layers have too few spots with too few MUs to allow the treatment delivery duration of the layer to be extended beyond the period T = 4s of the breathing cycle by the scan modes 1-7 of Figure 7. In such cases, the new scan technique with the repainting scheme shown in Figure 10 is used as an alternative according to an embodiment. As indicated in Figure 7, the scan modes 8a and 8b allow any number of repaintings (both even and odd numbers). Scan modes 8a and 8b are identical except that they are applicable for layers with duration equal to and smaller than the period T = 4s of the breathing cycle, respectively. Accordingly, the treatment delivery duration of the layer may be further increased at the cost of less evenly spread-out repaintings.

[0042] Referring again to Figure 10, the alternative available is used when the new scan technique with the quasi-periodic repainting scheme of Figures 8 and 9 fails to increase the treatment delivery duration of the layer beyond the period T = 4s of the breathing cycle because the layer has too few spots and MUs. As depicted in Figure 10, the two multi-paint repainting blocks 42 are identical and may include any number of paintings for a spot. The 1-paint repainting blocks 44 and 46 (1a and 1b) may include spots that are painted once as well as spots that are painted an odd number of times (n>3) and therefore also are placed in the multi-paint repainting blocks 42. The 1-paint repainting blocks 44 and 46 are split into block 1a and block 1b in order to get the timemulti between the multi-paint repainting blocks 42 as close to half the period T/2 = 2s of the breathing cycle as possible, which will reduce the interplay effect for spots in the multi-paint repainting blocks 42.

[0043] Some layers with a very high number of spots and MU may have a treatment delivery duration that exceeds the period T = 4s of the breathing cycle even with the slowest scan mode of Figure 7. For these layers, a treatment delivery duration of twice the period T2 = 8s of the breathing cycle covering two breathing cycles may be obtained in a similar manner as described above. For example, the new scan technique with the quasi-periodic repainting scheme similar to Figure 9 may be obtained for each of the two breathing cycles. Moreover, the spot scan pattern may be reversed for the first breathing cycle relative to the second breathing cycle in order to further smear out any residual interplay effect.

[0044] The new scan technique that integrates repainting was investigated for 13 clinical proton PBS fields. For each field, the treatment delivery of each layer was rearranged as shown in Figures 8, 9, and 10. Figure 11 shows a graph 50 with examples of the treatment delivery durations of layers for one field with a planned treatment delivery without use of the new scan technique while Figure 12 illustrates a graph 52 with examples of the treatment delivery durations of layers for one field with treatment delivery according Figures 9 (method 1) and 10 (method 2) according to an embodiment, where the times are calculated with equations (1)-(3) of Figure 2B. As shown in Figure 13, the graph 54 demonstrates that the actual treatment delivery times recorded in log files for 35 layers under the new scan technique are reasonably close to the predicted treatment delivery times with equations (1)-(3) of Figure 2B according to an embodiment.

[0045] Continuing, the treatment plans of five patients treated with proton PBS for thoracic and abdominal tumors were used for experimental dosimetric evaluation of the new scan technique. The five plans were two- or three-field plans with single-field-optimization in the treatment planning system and fraction doses between 1.8Gy and 4.5Gy. The tumors were pancreas, liver, lung/bronchus neoplasm, a non-small cell lung cancer tumor in right lower lobe, and a renal cell carcinoma. The plans represent a wide range of tumor sites, volumes, and doses. The five evaluation proton PBS plans had a total of 12 fields with 237 energy layers. The last two columns in Figure 7 show the percentage of layers and MUs for each of the eight scan modes. As depicted in Figure 7, all eight scan modes were used. Although 33.8% of the layers were scanned with the suboptimal scan mode 8b with <4s treatment delivery duration, these layers only constituted 6.5% of the total dose (or MU) as seen in the bottom row of Figure 7. The layers with less than 4s treatment delivery duration were often the most deep and shallow layers (first and last layers in the field) as in the examples in Figures 11-13. Further, 4.6% of the layers (2.3% of the dose or MU) were delivered with scan mode 8a with treatment delivery duration equal to 4s, but with repaintings that were less uniformly distributed throughout the breathing cycle than for scan modes 1-7.

[0046] The ability to mitigate the interplay effect of the new scan technique was investigated with a set-up illustrated in Figure 14 according to an embodiment. Each of the 12 proton PBS fields were delivered to an ion chamber array 62 carried by a motion stage 64. The ion chamber array 62 measured the 2D dose distribution with a frame rate of 0.1s. Blocks of solid water 66 on the ion chamber array 62 gave a measuring depth corresponding to a proximal end of the spread-out Bragg peak. Each field was delivered three times to the ion chamber array 62: Once without motion and twice with a 4s period, 3cm peak-to-peak, sinusoidal motion, where the treatment delivery was started at two different times relative to the motion cycle. For comparison, similar static + 2 x motion experiments were also performed (1) with the original default scan mode (without any repainting) and (2) with up to 8 times repaintings. In the latter case, all spots with >8MUmin were painted 8 times, while spots that could only be painted N times (N < 8) received N painting during the first N passes of the spot map. In total, 108 treatment deliveries were performed (12 fields X 3 repainting schemes X 3 motion cases).

[0047] For each motion experiment, the time resolved dose frames were summed in order to obtain the accumulated motion dose with the interplay effect as demonstrated in the upper row 72 of the block diagram 78 of Figure 15. This dose was then compared with a reference dose, which was the accumulated static dose smeared or convolved with the known sinusoidal phantom motion as demonstrated in the lower row 74 of the block diagram 78 of Figure 15. This reference dose represents an ideal motion dose distribution that is blurred due to motion, but otherwise without any interplay effect. The comparison with this reference dose was performed as a gamma test, where the percentage of ion chamber measurements fulfilling the 3%/3mm gamma pass criterion was reported. Ion chamber measurements with less than 10% of the maximum dose in the reference dose map were excluded in the gamma test.

[0048] Figure 16 depicts examples of measured doses with an ion chamber array for a patient under treatment according to an embodiment. Illustrated are a static dose (measured) 80, a static dose (blurred) 82 convolved with the applied 3cm peak-to-peak sinusoidal motion, i.e. the ideal smearedout interplay-effect-free dose distribution. The three right columns show measured motion doses with the default delivery (no repainting) 84 and 85, conventional 8-repainting delivery 86 and 87, and treatment delivery according to the new scan technique 88 and 89 in experiments with the treatment starting in cranial phantom position (upper row) and caudal phantom position (lower row). The listed numbers specify the 3%/3mm gamma pass rate of the motion doses when compared with the ideal blurred static dose (i.e., compared with the static dose (blurred) 82). The treatment delivery according to the new scan technique 88 and 89 had (1) considerably higher gamma pass rates (i.e., lower interplay effect) and (2) considerably less variations when comparing one motion experiment with another.

[0049] The results for 3 x 24 motion experiments are summarized in Figure 17 according to an embodiment, showing a clear and highly significant improvement with the treatment delivery according to the new scan technique. Mean (±1 standard deviation) of the 3%/3mm gamma pass rate in motion experiments with treatment delivered with the default scheme (upper row), with 8 repaintings (middle row), and with the new scan technique (lower row) when compared with a blurred static reference dose. Further, experimental results, simulations of the experiments, and simulations extended from 1 to 10 starting phases for each motion experiment are demonstrated in Figure 17.

[0050] Continuing, a series of simulations were performed in order to expand the scope of the investigation of the new scan technique beyond what is practically feasible with experiments. The measured motion doses were reproduced from the measured static doses.

[0051] For each of the 72 motion experiments, the time resolved 2D dose frames of the corresponding static experiment were first resampled to obtain the same number of dose frames for each energy layer as in the motion experiment as depicted in the block diagram 92 of Figure 18 according to an embodiment. Next, the shift of each frame in the motion experiment (i.e., the position of the motion stage at the moment of frame exposure) was determined as the shift that gave the highest normalized cross correlation with the corresponding frame in the static experiment. Finally, the shifts of all motion frames were fitted to the known 3cm, 4s period sinusoidal motion. As result of this procedure, the phantom position for all dose frames in the motion experiment was now known. This information was used to simulate the motion dose from the static dose by adding the known motion to each frame and summing up the frames as shown in Figure 18 (Simulated motion dose). The agreement between simulated and measured doses was very high with a mean 3%/3mm gamma pass rate of 99.4%. It shows that the static-measurement-based simulations can reproduce the motion doses with high accuracy.

[0052] Next, the ability of the simulations to reproduce the experimental gamma pass rates for the interplay effect was investigated as indicated with the block diagram 94 of Figure 19 according to an embodiment. As shown in the graph 96 of Figure 20 according to an embodiment, the simulations accurately reproduced the experimental 3%/3mm gamma pass rates with a root-mean-square error of 1.3 percent-spot. This is also shown in Figure 17 (compare first and second columns).

[0053] Simulations were used to investigate the impact of the motion amplitude as shown in the graph 110 of Figure 21 according to an embodiment. The new scan technique (optimized) largely reduced the interplay effect even with very large motion of 50mm. The mean gamma pass rate with 50mm motion for the new scan technique (optimized) was better than the mean gamma pass rate of 8 repaintings with only 10mm motion.

[0054] Further, the impact of a breathing period differing from period T = 4s was investigated as shown in the graph 120 of Figure 22 according to an embodiment. It is relevant to know how much the interplay effect mitigation of the new scan technique (optimized) degrades if the patient happens to have another breathing period at treatment than the one used for plan delivery optimization (period T = 4s). Although the interplay mitigation of the new scan technique (optimized) decreased with other motion periods, the mean gamma pass rate stayed above 85% for a wide range of breathing periods.

[0055] The smearing of the interplay effect with fractionated delivery was investigated as shown in the graph 130 of Figure 23 according to an embodiment by simulating all possible combinations of 10 motion starting phases at N fractions (N = 1-6) for all 72 motion experiments. The mean and standard deviation of the 3%/3mm gamma pass rate were calculated for all 10N possible combinations of N-fraction treatment courses for each motion experiment. The results are shown in Figure 23. The new scan technique (optimized) was clearly superior with a mean gamma pass rate after a single fraction (92.5%) that was equal to the mean gamma pass rate of 8 repaintings after 3.5 fractions, but with a much smaller standard deviation (error bars in Figure 23). The standard deviation was 4.6% after only 1 fraction delivered with the new scan technique (optimized) while it was still 5.7% after 6 fractions with 8 repaintings. It indicates the absence of outliers with large interplay effects for the new scan technique (optimized).

[0056] Continuing, the interplay effect was investigated for the actually measured tumor motion as measured for six liver SBRT patients during treatment delivery with kilovoltage intrafraction imaging (KIM) as shown in the graph 140 of Figure 24 according to an embodiment. The results are shown in Figure 24 for the measured motion at all fractions (6 patients x 3 fractions/patient). Unlike the sinusoidal motion studied so far, the patient-measured motion trajectories have many irregularities such as variations in waveform, period, and amplitude from cycle to cycle as well as baseline shifts. Although the new scan technique (optimized) was superior to 8 repaintings (and no repaintings) for all fractions, the gamma pass rate was somewhat low for Patients 2 and 4, who had very fast breathing periods of less than 3 seconds. The new scan technique (optimized) designed for this fast breathing would perform better than the current implementation aimed for period T = 4s for treatment delivery duration per energy layer.

[0057] As a final investigation of the interplay effect mitigation, delivery of all three proton PBS fields for the first patient in the study was simulated in a Matlab program with the three delivery schemes (optimized, 8 repaintings, default). The Matlab program distributed all spots in ten different breathing phases and generated a DICOM plan file for each breathing phase. A layer shift time of 1.1 seconds, a spot delivery time according to equations (1)-(3) of Figure 2B, and a breathing period T = 4s were assumed. The ten DICOM plans were imported into the ten phases of a 4DCT scan for the patient in a treatment planning system. The phase-specific dose was calculated in each 4DCT phase and summed in the full exhale phase using deformable image registration. As shown in Figure 25, the new scan technique (optimized) gave a superior dose distribution with fewer interplay effects according to an embodiment.

[0058] Figure 26 depicts a dose-volume histogram 150 for the internal clinical target volume (ICTV) of 4D dose reconstruction in a treatment planning system with the default delivery, with 8 repaintings, and with the new scan technique (optimized) for the first patient (pancreas) according to an embodiment. The new scan technique (optimized) leads to a more uniform target dose with fewer interplay effects.

[0059] The new scan technique may be implemented in many ways, notably as software running on a PC or similar. The presently disclosure further relates to a system for mitigating interplay effects in particle radiation therapy comprising a non-transitive, computer-readable storage device for storing instructions that performs a method for mitigating interplay effects in particle radiation therapy. The disclosure further relates to a computer program having instructions which when executed by a computing device or system causes the computing device or system to mitigate interplay effects in particle radiation therapy. Computer program should be construed broadly and include programs to be run on a PC, a part of the computer system facilities in a particle radiation therapy center, or software designed to run on smartphones, tablet computers or other mobile devices. Computer programs and mobile applications include software that is free and software that has to be bought, and also include software that is distributed over distribution software platforms.

[0060] The present disclosure further relates to a particle therapy system comprising a particle beam generator for creating a particle beam used for particle radiation therapy, a beam transfer unit for delivering the particle radiation therapy to a target, a beam scanning unit configured to scan the particle beam across the target, and a processing unit configured to generate a scan pattern for the beam scanning unit by means described above to mitigate interplay effect of the particle radiation therapy. The particle therapy system may for example be a part of a proton center with one or more cyclotron accelerators. In a further embodiment, the present disclosure relates to a method for treatment of a cancer tumor in a region of a patient under periodic movement by submitting a target volume of the tumor to particle radiation therapy. In still another embodiment, the period of movement of the cancer tumor is obtained. The target volume is divided into a plurality of layers. Each of the layers is divided into a plurality of spots. A planned dose of particle radiation therapy of each spot of the target volume is calculated. A scan pattern is generated by means of the herein disclosed. The particle radiation therapy is delivered to the target volume (e.g., a tumor) according to the scan pattern to mitigate interplay effect of the particle radiation therapy. The cancer tumor (or several of them) may for example be located in the abdominal or the thoracic regions of the patient. But, cancer tumors in other anatomical regions may also be relevant, in particular if they are under influence of periodic movements during the particle radiation therapy.

[0061] The foregoing descriptions of specific embodiments have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, to thereby enable others skilled in the art to best utilize the disclosure and various embodiments with various modifications as are suited to the particular use contemplated.


Claims

1. A system configured to generate a radiation treatment plan by performing a method of mitigating interplay effect in particle radiation therapy for delivery to a moving target including a period of movement, the particle radiation therapy defining a planned dose in each spot of each layer of the moving target, the method comprising:

dividing the planned dose in each spot into a number of spot repaintings; and

generating a scan pattern for each layer by

defining a beam-on time (16) at each spot for each spot repainting, and

calculating a wait time (14) between consecutive beam-on times to distribute the spot repaintings for each spot of a respective layer over a duration of an integer number of periods of movement.


 
2. The system according to claim 1, configured so that the number of spot repaintings at each spot is maximized according to a predefined minimum dose per spot of the particle radiation therapy.
 
3. The system according to claim 1, configured so that the spot repaintings of each spot of a layer are distributed evenly over the duration of the integer number of periods of movement.
 
4. The system according to claim 1, configured so that the number of spot repaintings for each spot is sorted into blocks (30, 32, 34, 36, 38), wherein the number of spot repaintings in each block (30, 32, 34, 36, 38) is an integer power of two.
 
5. The system according to claim 4, configured so that the spot repaintings of each block (30, 32, 34, 36, 38) are distributed evenly over an integer number of periods of movement.
 
6. The system according to claim 1, configured so that the spot repaintings in the scan pattern are distributed by adjusting a sequence order of spots and/or spot repaintings in a layer and/or the wait time (14) between consecutive beam-on times (16) in a layer.
 
7. The system according to claim 1, configured so that the wait time (14) between consecutive beam-on times (16) in a layer is adjusted by selecting a beam pause before one or more spots in the scan pattern.
 
8. The system according to claim 1, wherein particles for the particle radiation therapy are from the group of: protons, ions, neutrons, and electrons;
and/or
wherein the system is configured so that the particle radiation therapy is conducted using pencil beam scanning.
 
9. The system according to claim 1, wherein the period of movement is due to breathing and/or heartbeat of a patient comprising the moving target,
and/or
wherein the breathing and/or heartbeat movement includes a breathing and/or heartbeat period and is determined with four-dimensional computed tomography.
 
10. The system according to claim 1 further configured:

for assisting synchronization of breathing of a patient and the period of movement; and/or

so that the patient is assisted by audio and/or visual guidance.


 
11. The system according to claim 1, configured so that the scan pattern is generated such that spot repaintings of spots in a layer that are irradiated once are distributed such that a first group (30, 1a) of the spots are irradiated during a first part of the period of the periodic movement and a second group (30, 1b) of the spots are irradiated during a second part of the period of the movement.
 
12. The system according to claim 1, configured so that the scan pattern is generated such that layers with scan times of two periods are scanned such that repainting blocks (32) of two or more spot repaintings are separated into two identical scan patterns, wherein a first scan pattern is performed in a first period of two periods and a second scan pattern is performed in a second period of two periods.
 
13. The system according to claim 1, configured so that the scan pattern is generated such that layers with scan times of two periods are scanned such that repainting blocks (32, 34, 36, 38) of two or more spot repaintings are separated into two scan patterns, wherein a first scan pattern is performed in a first period and a second scan is performed in a second period, and wherein the second scan pattern is the reverse of the first scan pattern.
 
14. The system according to claim 1, configured so that the scan pattern is generated such that layers with a scan time duration less than the period of the movement are scanned using a pattern with a maximum scan time duration.
 
15. A computer-implemented method for generating a scan pattern for treatment of a cancer tumor in a region of a patient under periodic movement by submitting a target volume of the tumor to particle radiation therapy, the
method comprising:

obtaining a period of movement of the cancer tumor;

dividing the target volume into a plurality of layers and dividing each of the layers into a plurality of spots;

calculating a planned dose of the particle radiation therapy of each spot of the target volume and dividing the planned dose in each spot of each layer into a number of spot repaintings; and

generating a scan pattern for each layer by defining a beam-on time (16) at each spot for each spot repainting and calculating a wait time (14) between consecutive beam-on times to distribute the spot repaintings for each spot of a respective layer over a duration of an integer number of periods of movement.


 


Ansprüche

1. System, welches dazu konfiguriert ist, einen Strahlentherapieplan durch ein Durchführen eines Verfahrens zum Abschwächen einer Wechselwirkung bei einer Partikelstrahlentherapie zum Liefern an ein sich bewegendes Ziel zu erzeugen, welches einen Bewegungszeitraum beinhaltet, wobei die Partikelstrahlentherapie eine geplante Dosis an jedem Punkt jeder Schicht des sich bewegenden Ziels definiert, wobei das Verfahren Folgendes umfasst:

Teilen der geplanten Dosis an jedem Punkt in eine Anzahl von punktuellen Repaintings; und

Erzeugen eines Abtastmusters für jede Schicht durch ein Definieren einer Strahl-an-Zeit (16) an jedem Punkt für jedes punktuelle Repainting, und

Berechnen einer Wartezeit (14) zwischen konsekutiven Strahl-an-Zeiten, um die punktuellen Repaintings für jeden Punkt einer entsprechenden Schicht über eine Dauer einer ganzzahligen Anzahl von Bewegungszeiträumen zu verteilen.


 
2. System nach Anspruch 1, welches dazu konfiguriert ist, dass die Anzahl von punktuellen Repaintings an jedem Punkt gemäß einer vorbestimmten Mindestdosis pro Punkt der Partikelstrahlentherapie maximiert ist.
 
3. System nach Anspruch 1, welches dazu konfiguriert ist, dass die punktuellen Repaintings jedes Punkts einer Schicht gleichmäßig über die Dauer einer ganzzahligen Anzahl von Bewegungszeiträumen verteilt sind.
 
4. System nach Anspruch 1, welches dazu konfiguriert ist, dass die Anzahl von punktuellen Repaintings für jeden Punkt in Blöcke (30, 32, 34, 36, 38) sortiert ist, wobei die Anzahl von punktuellen Repaintings in jedem Block (30, 32, 34, 36, 38) eine ganzzahlige Zweierpotenz ist.
 
5. System nach Anspruch 4, welches dazu konfiguriert ist, dass die punktuellen Repaintings jedes Blocks (30, 32, 34, 36, 38) gleichmäßig über eine ganzzahlige Anzahl von Bewegungszeiträumen verteilt sind.
 
6. System nach Anspruch 1, welches dazu konfiguriert ist, dass die punktuellen Repaintings in dem Abtastmuster verteilt sind durch ein Anpassen einer Sequenzreihenfolge von Punkten und/oder punktuellen Repaintings in einer Schicht und/oder der Wartezeit (14) zwischen konsekutiven Strahl-an-Zeiten (16) in einer Schicht.
 
7. System nach Anspruch 1, welches dazu konfiguriert ist, dass die Wartezeit (14) zwischen konsekutiven Strahl-an-Zeiten (16) in einer Schicht angepasst ist durch ein Auswählen einer Strahlenpause vor einem oder mehreren Punkten in dem Abtastmuster.
 
8. System nach Anspruch 1, wobei Partikel für die Partikelbestrahlungstherapie aus der Gruppe von Folgendem sind:

Protonen, Ionen, Neutronen und Elektronen;
und/oder

wobei das System dazu konfiguriert ist, dass die Partikelstrahlentherapie mithilfe eines Nadelstrahlabtastens ausgeführt wird.


 
9. System nach Anspruch 1, wobei der Bewegungszeitraum aufgrund von Atmung und/oder Herzschlag eines Patienten ist, welcher das sich bewegende Ziel umfasst,
und/oder
wobei die Atmungs- und/oder der Herzschlagbewegung eine Atmungs- und/oder einen Herzschlagzeitraum beinhaltet und mit vierdimensionaler Computertomografie bestimmt wird.
 
10. System nach Anspruch 1, welches ferner konfiguriert ist:

zum Unterstützen einer Synchronisation einer Atmung eines Patienten und des Bewegungszeitraum;
und/oder

dass der Patient durch Audio- und/oder Videoanweisung unterstützt wird.


 
11. System nach Anspruch 1, welches dazu konfiguriert ist, dass das Abtastmuster erzeugt wird, so dass punktuelle Repaintings von Punkten in einer Schicht, welche einmal bestrahlt werden, so verteilt werden, dass eine erste Gruppe (30, 1a) der Punkte während eines ersten Teils des Zeitraums der periodischen Bewegung bestrahlt wird und eine zweite Gruppe (30, 1b) der Punkte während eines zweiten Teils des Bewegungszeitraums bestrahlt wird.
 
12. System nach Anspruch 1, welches dazu konfiguriert ist, dass das Abtastmuster erzeugt wird, so dass Schichten mit Abtastzeiten von zwei Zeiträumen abgetastet werden, so dass Erneuerungsanstrichblöcke (32) aus zwei oder mehr punktuellen Repaintings in zwei identische Abtastmuster getrennt werden, wobei ein erstes Abtastmuster in einem ersten Zeitraum aus zwei Zeiträumen durchgeführt wird und ein zweites Abtastmuster in einem zweiten Zeitraum aus zwei Zeiträumen durchgeführt wird.
 
13. System nach Anspruch 1, welches dazu konfiguriert ist, dass das Abtastmuster erzeugt wird, so dass Schichten mit Abtastzeiten von zwei Zeiträumen abgetastet werden, so dass Erneuerungsanstrichblöcke (32, 34, 36, 38) aus zwei oder mehr punktuellen Repaintings in zwei Abtastmuster getrennt werden, wobei ein erstes Abtastmuster in einem ersten Zeitraum durchgeführt wird und ein zweites Abtastmuster in einem zweiten Zeitraum durchgeführt wird, und wobei das zweite Abtastmuster umgekehrt zu dem ersten Abtastmuster ist.
 
14. System nach Anspruch 1, welches dazu konfiguriert ist, dass das Abtastmuster erzeugt wird, so dass Schichten mit einer Abtastzeitdauer, welche geringer ist als der Bewegungszeitraum, unter Verwendung eines Musters mit einer maximalen Abtastzeitdauer abgetastet werden.
 
15. Computerimplementiertes Verfahren zum Erzeugen eines Abtastmusters zur Behandlung eines Krebstumors in einem Bereich eines Patienten, welcher periodischen Bewegungen unterliegt, indem ein Zielvolumen des Tumors einer Partikelstrahlentherapie unterzogen wird, wobei das Verfahren Folgendes umfasst:

Erlangen eines Bewegungszeitraums des Krebstumors;

Teilen des Zielvolumens in eine Vielzahl von Schichten und Teilen jeder der Schichten in eine Vielzahl von Punkten;

Berechnen einer geplanten Dosis der Partikelstrahlentherapie jedes Punkts des Zielvolumens und Teilen der geplanten Dosis in jedem Punkt jeder Schicht in eine Anzahl von punktuellen Repaintings; und

Erzeugen eines Abtastmusters für jede Schicht durch ein Definieren einer Strahl-an-Zeit (16) an jedem Punkt für jedes punktuelle Repainting und Berechnen einer Wartezeit (14) zwischen konsekutiven Strahl-an-Zeiten, um die punktuellen Repaintings für jeden Punkt einer entsprechenden Schicht über eine Dauer einer ganzzahligen Anzahl von Bewegungszeiträumen zu verteilen.


 


Revendications

1. Système configuré pour générer un plan de traitement par rayonnement en exécutant une méthode d'atténuation de l'effet d'interactions dans une thérapie par rayonnement de particules destinée à la livraison à une cible mobile comportant une période de mouvement, la thérapie par rayonnement de particules définissant une dose prévue dans chaque point de chaque couche de la cible mobile, le procédé comprenant :

la division de la dose prévue à chaque point en un certain nombre de re-balayages de point ; et

la génération d'un motif de balayage destiné à chaque couche par la définition d'un temps d'activation de faisceau (16) à chaque point pour chaque re-balayage de point, et

le calcul d'un temps d'attente (14) entre des temps consécutifs d'activation de faisceau pour répartir les re-balayages de point pour chaque point d'une couche respective sur une durée d'un nombre entier de périodes de mouvement.


 
2. Système selon la revendication 1, configuré de sorte que le nombre de re-balayages de point à chaque point est maximisé en fonction d'une dose minimale prédéfinie par point de la thérapie par rayonnement de particules.
 
3. Système selon la revendication 1, configuré de sorte que les re-balayages de point de chaque point d'une couche sont répartis uniformément sur la durée du nombre entier de périodes de mouvement.
 
4. Système selon la revendication 1, configuré de sorte que le nombre de re-balayages de point pour chaque point est trié en blocs (30, 32, 34, 36, 38), dans lequel le nombre de re-balayages de point dans chaque bloc (30, 32, 34, 36, 38) est une puissance entière de deux.
 
5. Système selon la revendication 4, configuré de sorte que les re-balayages de point de chaque bloc (30, 32, 34, 36, 38) sont répartis uniformément sur un nombre entier de périodes de mouvement.
 
6. Système selon la revendication 1, configuré de sorte que les re-balayages de point dans le motif de balayage sont répartis en ajustant un ordre de séquence de points et/ou de re-balayages de point dans une couche et/ou le temps d'attente (14) entre des temps consécutifs d'activation de faisceau (16) dans une couche.
 
7. Système selon la revendication 1, configuré de sorte que le temps d'attente (14) entre des temps consécutifs d'activation de faisceau (16) dans une couche est ajusté en sélectionnant une pause de faisceau avant un ou plusieurs points dans le motif de balayage.
 
8. Système selon la revendication 1, dans lequel les particules destinées à la thérapie par rayonnement de particules proviennent du groupe : des protons, des ions, des neutrons et des électrons ;
et/ou
dans lequel le système est configuré de sorte que la thérapie par rayonnement de particules est effectuée en utilisant un balayage par faisceau étroit.
 
9. Système selon la revendication 1, dans lequel la période de mouvement est due à la respiration et/ou au battement de cœur d'un patient comprenant la cible mobile,
et/ou
dans lequel le mouvement de respiration et/ou de battement de cœur comporte une période de respiration et/ou de battement de cœur et est déterminé par tomodensitométrie en quatre dimensions.
 
10. Système selon la revendication 1 configuré en outre :

pour assister la synchronisation de la respiration d'un patient et de la période de mouvement ;
et/ou

de sorte que le patient est assisté par un guidage audio et/ou visuel.


 
11. Système selon la revendication 1, configuré de sorte que le motif de balayage est généré de sorte que des re-balayages de point dans une couche qui sont irradiés une fois sont répartis de sorte qu'un premier groupe (30, 1a) de points est irradié durant une première partie de la période du mouvement périodique et un second groupe (30, 1b) de points est irradié durant une seconde partie de la période du mouvement.
 
12. Système selon la revendication 1, configuré de sorte que le motif de balayage est généré de sorte que des couches avec des temps de balayage de deux périodes sont balayées de sorte que les blocs de re-balayages (32) de deux re-balayages de point ou plus sont séparés en deux motifs de balayage identiques, dans lequel un premier motif de balayage est réalisé dans une première période de deux périodes et un second motif de balayage est réalisé dans une seconde période de deux périodes.
 
13. Système selon la revendication 1, configuré de sorte que le motif de balayage est généré de sorte que des couches avec des temps de balayage de deux périodes sont balayées de sorte que les blocs de re-balayages (32, 34, 36, 38) de deux re-balayages de point ou plus sont séparés en deux motifs de balayage, dans lequel un premier motif de balayage est réalisé dans une première période et un second balayage est réalisé dans une seconde période, et dans lequel le second motif de balayage est l'inverse du premier motif de balayage.
 
14. Système selon revendication 1, configuré de sorte que le motif de balayage est généré de sorte que des couches ayant une durée de temps de balayage inférieure à la période du mouvement sont balayées en utilisant un motif avec une durée de temps de balayage maximale.
 
15. Procédé mis en œuvre par ordinateur destiné à la génération d'un motif de balayage pour le traitement d'une tumeur cancéreuse dans une région d'un patient soumis à un mouvement périodique en soumettant un volume cible de la tumeur à la thérapie par rayonnement de particules, le procédé comprenant :

l'obtention d'une période de mouvement de la tumeur cancéreuse ;

la division du volume cible en une pluralité de couches et la division de chacune des couches en une pluralité de points ;

le calcul d'une dose prévue de la thérapie par rayonnement de particules de chaque point du volume cible et la division de la dose prévue dans chaque point de chaque couche en un nombre de re-balayages de point ; et

la génération d'un motif de balayage pour chaque couche en définissant un temps d'activation de faisceau (16) à chaque point pour chaque re-balayage de point et en calculant un temps d'attente (14) entre des temps consécutifs d'activation de faisceau pour répartir les re-balayages de point pour chaque point d'une couche respective sur une durée d'un nombre entier de périodes de mouvement.


 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Patent documents cited in the description