Fracchiolla F, Lorentini S, Widesott L, Schwarz M
Azienda Provinciale per i Servizi Sanitari (APSS) Protontherapy Department, Trento, Italy. Post Graduate School of Medical Physics 'Sapienza' University of Rome, 00185 Roma, Italy.
Phys Med Biol. 2015 Nov 7;60(21):8601-19. doi: 10.1088/0031-9155/60/21/8601. Epub 2015 Oct 26.
We propose a method of creating and validating a Monte Carlo (MC) model of a proton Pencil Beam Scanning (PBS) machine using only commissioning measurements and avoiding the nozzle modeling. Measurements with a scintillating screen coupled with a CCD camera, ionization chamber and a Faraday Cup were used to model the beam in TOPAS without using any machine parameter information but the virtual source distance from the isocenter. Then the model was validated on simple Spread Out Bragg Peaks (SOBP) delivered in water phantom and with six realistic clinical plans (many involving 3 or more fields) on an anthropomorphic phantom. In particular the behavior of the moveable Range Shifter (RS) feature was investigated and its modeling has been proposed. The gamma analysis (3%,3 mm) was used to compare MC, TPS (XiO-ELEKTA) and measured 2D dose distributions (using radiochromic film). The MC modeling proposed here shows good results in the validation phase, both for simple irradiation geometry (SOBP in water) and for modulated treatment fields (on anthropomorphic phantoms). In particular head lesions were investigated and both MC and TPS data were compared with measurements. Treatment plans with no RS always showed a very good agreement with both of them (γ-Passing Rate (PR) > 95%). Treatment plans in which the RS was needed were also tested and validated. For these treatment plans MC results showed better agreement with measurements (γ-PR > 93%) than the one coming from TPS (γ-PR < 88%). This work shows how to simplify the MC modeling of a PBS machine for proton therapy treatments without accounting for any hardware components and proposes a more reliable RS modeling than the one implemented in our TPS. The validation process has shown how this code is a valid candidate for a completely independent treatment plan dose calculation algorithm. This makes the code an important future tool for the patient specific QA verification process.
我们提出了一种仅使用调试测量来创建和验证质子笔形束扫描（PBS）机器的蒙特卡罗（MC）模型的方法，且无需对喷嘴进行建模。使用与电荷耦合器件（CCD）相机耦合的闪烁屏、电离室和法拉第杯进行测量，以在TOPAS中对束流进行建模，除了距等中心的虚拟源距离外，不使用任何机器参数信息。然后，该模型在水模体中递送的简单扩展布拉格峰（SOBP）以及在人体模型上的六个实际临床计划（许多涉及3个或更多射野）上进行了验证。特别研究了可移动射程移位器（RS）功能的行为，并提出了其建模方法。使用伽马分析（3%，3毫米）来比较MC、治疗计划系统（TPS，XiO - 医科达）和测量的二维剂量分布（使用放射变色胶片）。这里提出的MC建模在验证阶段显示出良好的结果，无论是对于简单的照射几何形状（水模体中的SOBP）还是对于调制治疗射野（在人体模型上）。特别对头部病变进行了研究，并将MC和TPS数据与测量结果进行了比较。没有RS的治疗计划始终与两者都显示出非常好的一致性（伽马通过率（PR）> 95%）。需要RS的治疗计划也进行了测试和验证。对于这些治疗计划，MC结果与测量结果的一致性（伽马 - PR > 93%）优于TPS的结果（伽马 - PR < 88%）。这项工作展示了如何在不考虑任何硬件组件的情况下简化用于质子治疗的PBS机器的MC建模，并提出了一种比我们的TPS中实现的更可靠的RS建模方法。验证过程表明，该代码是完全独立的治疗计划剂量计算算法的有效候选者。这使得该代码成为患者特定质量保证验证过程的重要未来工具。
