Roy J. Carver Department of Biomedical Engineering, University of Iowa, 5601 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa, USA.
Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA.
Med Phys. 2023 Nov;50(11):7263-7280. doi: 10.1002/mp.16559. Epub 2023 Jun 27.
The Dynamic Collimation System (DCS) has been shown to produce superior treatment plans to uncollimated pencil beam scanning (PBS) proton therapy using an in-house treatment planning system (TPS) designed for research. Clinical implementation of the DCS requires the development and benchmarking of a rigorous dose calculation algorithm that accounts for pencil beam trimming, performs monitor unit calculations to produce deliverable plans at all beam energies, and is ideally implemented with a commercially available TPS.
To present an analytical Pencil bEam TRimming Algorithm (PETRA) for the DCS, with and without its range shifter, implemented in the Astroid TPS (.decimal, Sanford, Florida, USA).
PETRA was derived by generalizing an existing pencil beam dose calculation model to account for the DCS-specific effects of lateral penumbra blurring due to the nickel trimmers in two different planes, integral depth dose variation due to the trimming process, and the presence and absence of the range shifter. Tuning parameters were introduced to enable agreement between PETRA and a measurement-validated Dynamic Collimation Monte Carlo (DCMC) model of the Miami Cancer Institute's IBA Proteus Plus system equipped with the DCS. Trimmer position, spot position, beam energy, and the presence or absence of a range shifter were all used as variables for the characterization of the model. The model was calibrated for pencil beam monitor unit calculations using procedures specified by International Atomic Energy Agency Technical Report Series 398 (IAEA TRS-398).
The integral depth dose curves (IDDs) for energies between 70 MeV and 160 MeV among all simulated trimmer combinations, with and without the ranger shifter, agreed between PETRA and DCMC at the 1%/1 mm 1-D gamma criteria for 99.99% of points. For lateral dose profiles, the median 2-D gamma pass rate for all profiles at 1.5%/1.5 mm was 99.99% at the water phantom surface, plateau, and Bragg peak depths without the range shifter and at the surface and Bragg peak depths with the range shifter. The minimum 1.5%/1.5 mm gamma pass rates for the 2-D profiles at the water phantom surface without and with the range shifter were 98.02% and 97.91%, respectively, and, at the Bragg peak, the minimum pass rates were 97.80% and 97.5%, respectively.
The PETRA model for DCS dose calculations was successfully defined and benchmarked for use in a commercially available TPS.
动态准直系统（DCS）已被证明能够产生优于未经准直铅笔束扫描（PBS）质子治疗的治疗计划，使用专为研究设计的内部治疗计划系统（TPS）。DCS 的临床实施需要开发和基准测试严格的剂量计算算法，该算法考虑到铅笔束修整，执行监视器单位计算，以便在所有射束能量下生成可交付的计划，并且理想情况下是在商业上可用的 TPS 中实现。
提出一种用于 DCS 的分析性铅笔束修剪算法（PETRA），具有和不具有其射程移位器，在 Astroid TPS（.decimal，Sanford，Florida，USA）中实现。
通过将现有的铅笔束剂量计算模型推广到考虑由于镍修整器在两个不同平面上引起的侧向半影模糊、修整过程引起的积分深度剂量变化以及射程移位器的存在和不存在的 DCS 特定影响，推导出了 PETRA。引入了调整参数，以使 PETRA 与经过测量验证的迈阿密癌症研究所 IBA Proteus Plus 系统配备 DCS 的动态准直蒙特卡罗（DCMC）模型之间达成一致。修整器位置、斑点位置、射束能量以及射程移位器的存在与否都被用作模型特征的变量。使用国际原子能机构技术报告系列 398（IAEA TRS-398）规定的程序对铅笔束监视器单位计算进行了模型校准。
在所有模拟修整器组合中，能量在 70 MeV 至 160 MeV 之间的积分深度剂量曲线（IDDs），以及具有和不具有射程移位器的情况下，在 1%/1 mm 1-D 伽马标准下，PETRA 与 DCMC 的一致性达到 99.99%。对于侧向剂量分布，在没有和有射程移位器的情况下，在水模表面、平台和布拉格峰值深度处，所有分布的中位数 2-D 伽马通过率为 99.99%，在水模表面和布拉格峰值深度处。在没有和有射程移位器的情况下，水模表面 2-D 分布的最小 1.5%/1.5 mm 伽马通过率分别为 98.02%和 97.91%，在布拉格峰值处，最小通过率分别为 97.80%和 97.5%。
成功定义了用于商业上可用 TPS 的 DCS 剂量计算的 PETRA 模型，并对其进行了基准测试。
