Granville D, Chequers M, Sawakuchi G
Carleton University, Ottawa, ON.
Med Phys. 2012 Jun;39(6Part9):3707. doi: 10.1118/1.4735076.
To investigate the validity of using the residual range as a universal quantity to specify the quality of modulated proton beams.
We used TOPAS (Tool for Particle Simulation), an application of the Geant4 toolkit, to simulate absorbed dose and stopping-power distributions from a commercial passive scattering nozzle. We used the standard physics lists from Geant4 in the simulations. All particles were included, as well as physics models for nuclear interactions. No variance reduction techniques were used. Dose and averaged stopping-power as functions of depth were scored in a water box with 320 scoring volumes of 15 × 15 × 0.1 cm . Stopping-power spectra were scored in a15 × 15 × 0.1 cm volume located in the middle of SOBPs. All particles were considered in the dose scoring. Only protons (primary and secondary) were considered in the scoring of stopping-power.
For the same residual range, differences in averaged stopping-power values of up to 13% were observed for a 200 MeV beam with modulations of 4 cm and 8 cm, respectively. Simulations of four modulated proton energies with the same SOBP of 8 cm showed differences of up to 13% in the averaged stopping-power values even in the SOBP region. We also simulated stopping power spectra in the middle of 8 cm SOBPs for four modulated proton energies. The averaged stopping-power values calculated from the spectra were within 3%, however, their distributions were very different with full width at half-maximum 150% larger for the 250 MeV beam compared to that of the 140 MeV beam.
Large differences in the averaged stopping-power values and stopping-power spectra were observed for the same residual range. Determining whether these differences have a significant effect on the response of radiation detectors exposed to proton beams requires further investigation. Natural Sciences and Engineering Research Council of Canada and Ontario Graduate Scholarship Program, Ontario Ministry of Training, Colleges and Universities.
研究将剩余射程作为一个通用量来指定调制质子束质量的有效性。
我们使用TOPAS（粒子模拟工具），它是Geant4工具包的一个应用程序，来模拟来自商业被动散射喷嘴的吸收剂量和阻止本领分布。在模拟中我们使用了Geant4的标准物理列表。所有粒子都被纳入，以及核相互作用的物理模型。未使用方差减少技术。剂量和平均阻止本领作为深度的函数在一个水模体中进行计分，该水模体有320个15×15×0.1 cm的计分体积。阻止本领谱在位于扩展布拉格峰（SOBP）中间的一个15×15×0.1 cm体积内进行计分。在剂量计分中考虑所有粒子。在阻止本领计分中仅考虑质子（初级和次级）。
对于相同的剩余射程，分别调制为4 cm和8 cm的200 MeV束，观察到平均阻止本领值的差异高达13%。对具有相同8 cm SOBP的四种调制质子能量进行模拟，即使在SOBP区域，平均阻止本领值的差异也高达13%。我们还对四种调制质子能量在8 cm SOBP中间模拟了阻止本领谱。从谱中计算出的平均阻止本领值在3%以内，然而，它们的分布非常不同，250 MeV束的半高宽比140 MeV束大150%。
对于相同的剩余射程，观察到平均阻止本领值和阻止本领谱存在很大差异。确定这些差异是否对暴露于质子束的辐射探测器的响应有显著影响需要进一步研究。加拿大自然科学与工程研究理事会以及安大略省研究生奖学金计划、安大略省培训、学院和大学部。
