Jensen Simon V, Muren Ludvig P, Balling Peter, Petersen Jørgen Bb, Valdetaro Lia B, Poulsen Per R
Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark.
Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
Phys Med Biol. 2022 Nov 25;67(23). doi: 10.1088/1361-6560/ac9fa2.
Proton therapy with pencil beam delivery enables dose distributions that conform tightly to the shape of a target. However, proton therapy dose delivery is sensitive to motion and deformation, which especially occur in the abdominal and thoracic regions. In this study, the dose perturbation caused by dynamic motion with and without gating during proton pencil beam deliveries were investigated using deformable three-dimensional (3D) silicone-based radiochromic dosimeters.A spread-out Bragg peak formed by four proton spots with different energies was delivered to two dosimeter batches. All dosimeters were cylindrical with a 50 mm diameter and length. The dosimeters were irradiated stationary while uncompressed and during dynamic compression by sinusoidal motion with peak-to-peak amplitudes of 20 mm in one end of the dosimeter and 10 mm in the other end. Motion experiments were made without gating and with gating near the uncompressed position. The entire experiment was video recorded and simulated in a Monte Carlo (MC) program.The 2%/2 mm gamma index analysis between the dose measurements and the MC dose simulations had pass rates of 86%-94% (first batch) and 98%-99% (second batch). Compared to the static delivery, the dose delivered during motion had gamma pass rates of 99%-100% when employing gating and 68%-87% without gating in the experiments whereas for the MC simulations it was 100% with gating and 66%-82% without gating.This study demonstrated the ability of using deformable 3D dosimeters to measure dose perturbations in proton pencil beam deliveries caused by dynamic motion and deformation.
笔形束扫描质子治疗能够实现与靶区形状紧密匹配的剂量分布。然而，质子治疗的剂量传递对运动和变形很敏感，这在腹部和胸部区域尤为常见。在本研究中，使用基于硅酮的可变形三维（3D）放射变色剂量计，研究了质子笔形束扫描过程中动态运动（有无门控）所引起的剂量扰动。由四个不同能量的质子点形成的扩展布拉格峰被输送到两批剂量计中。所有剂量计均为圆柱形，直径和长度均为50 mm。剂量计在未压缩状态下静止照射，并在动态压缩过程中照射，动态压缩通过正弦运动实现，剂量计一端的峰峰值幅度为20 mm，另一端为10 mm。运动实验在无门控和在未压缩位置附近有门控的情况下进行。整个实验进行了视频记录，并在蒙特卡罗（MC）程序中进行了模拟。剂量测量与MC剂量模拟之间的2%/2 mm伽马指数分析通过率在第一批中为86%-94%，第二批中为98%-99%。与静态输送相比，在实验中，运动过程中输送的剂量在采用门控时伽马通过率为99%-100%，无门控时为68%-87%；而对于MC模拟，有门控时为100%，无门控时为66%-82%。本研究证明了使用可变形3D剂量计测量质子笔形束扫描过程中动态运动和变形所引起的剂量扰动的能力。
