Center for Proton Therapy, Paul Scherrer Institute, 5232 Villigen PSI, CH, Switzerland.
Department of Physics, ETH Zürich, 8092 Zürich, CH, Switzerland.
Phys Med Biol. 2023 Sep 26;68(19). doi: 10.1088/1361-6560/acf90d.
Magnetic resonance (MR) is an innovative technology for online image guidance in conventional radiotherapy and is also starting to be considered for proton therapy as well. For MR-guided therapy, particularly for online plan adaptations, fast dose calculation is essential. Monte Carlo (MC) simulations, however, which are considered the gold standard for proton dose calculations, are very time-consuming. To address the need for an efficient dose calculation approach for MRI-guided proton therapy, we have developed a fast GPU-based modification of an analytical dose calculation algorithm incorporating beam deflections caused by magnetic fields.Proton beams (70-229 MeV) in orthogonal magnetic fields (0.5/1.5 T) were simulated using TOPAS-MC and central beam trajectories were extracted to generate look-up tables (LUTs) of incremental rotation angles as a function of water-equivalent depth. Beam trajectories are then reconstructed using these LUTs for the modified ray casting dose calculation. The algorithm was validated against MC in water, different materials and for four example patient cases, whereby it has also been fully incorporated into a treatment plan optimisation regime.Excellent agreement between analytical and MC dose distributions could be observed with sub-millimetre range deviations and differences in lateral shifts <2 mm even for high densities (1000 HU). 2%/2 mm gamma pass rates were comparable to the 0 T scenario and above 94.5% apart for the lung case. Further, comparable treatment plan quality could be achieved regardless of magnetic field strength.A new method for accurate and fast proton dose calculation in magnetic fields has been developed and successfully implemented for treatment plan optimisation.
磁共振（MR）是一种创新的在线图像引导技术，不仅在常规放射治疗中得到应用，而且也开始在质子治疗中得到考虑。对于 MR 引导治疗，特别是在线计划调整，快速剂量计算至关重要。然而，蒙特卡罗（MC）模拟被认为是质子剂量计算的金标准，非常耗时。为了满足 MRI 引导质子治疗中高效剂量计算方法的需求，我们开发了一种快速 GPU 修正的分析剂量计算算法，该算法结合了磁场引起的射束偏转。使用 TOPAS-MC 模拟了正交磁场（0.5/1.5 T）中的质子束（70-229 MeV），并提取了中心射束轨迹，以生成增量旋转角度的查找表（LUT），作为水当量深度的函数。然后，使用这些 LUT 对修正的射线追踪剂量计算进行射束轨迹重建。该算法在水中、不同材料以及四个示例患者病例中与 MC 进行了验证，并且已经完全纳入治疗计划优化系统。分析和 MC 剂量分布之间可以观察到极好的一致性，毫米级范围内的偏差和侧向移位的差异<2mm，即使对于高密度（1000 HU）也是如此。2%/2mm 伽马通过率与 0 T 情况相当，而在肺部病例中则超过 94.5%。此外，无论磁场强度如何，都可以实现可比的治疗计划质量。已经开发出一种在磁场中进行准确快速质子剂量计算的新方法，并已成功用于治疗计划优化。
