Radiation Oncology and Winship Cancer Institute, Emory University, 1365 Clifton Rd NE, Atlanta, GA 30322, USA.
Nuclear and Radiological Engineering, Georgia Institute of Technology, 770 State St NW, Atlanta, GA 30332, USA.
Radiat Prot Dosimetry. 2020 Jul 13;189(2):190-197. doi: 10.1093/rpd/ncaa030.
New technique is trending in spatially fractionated radiotherapy with protons to utilize the spot scanning together with a physical collimator to obtain minibeams. The primary goal of this study is to quantify ambient neutron dose equivalent (${H}^{\ast }(10)$) due to the secondary neutrons when physical collimator is used to achieve desired minibeams. The ${H}^{\ast }(10)$ per treatment proton dose (D) was assessed using Monte Carlo code TOPAS and measured using WENDI-II detector at different angles (135, 180, 225 and 270 degrees) and distances (11 cm, 58 and 105 cm) from the phantom for two cases: with and without physical collimation. Without collimation $\frac{H^{\ast }(10)}{D}$ varied from 0.0013 to 0.242 mSv/Gy. With collimation $\frac{H^{\ast }(10)}{D}$ varied from 0.017 to 3.23 mSv/Gy. Results show that the secondary neutron dose will increase tenfold when the physical collimator is used. Regardless, it will be low and comparable to the neutron dose produced by conventional passive-scattered proton beams.
新的技术在质子空间分割放射治疗中流行，利用点扫描和物理准直器来获得微束。这项研究的主要目的是量化由于使用物理准直器实现所需微束而产生的次级中子的环境中子剂量当量（${H}^{\ast }(10)$）。使用蒙特卡罗代码 TOPAS 评估每个治疗质子剂量（D）的 ${H}^{\ast }(10)$，并使用 WENDI-II 探测器在不同角度（135、180、225 和 270 度）和距离（11 厘米、58 厘米和 105 厘米）从体模进行测量，对于两种情况：有和没有物理准直。无准直时，$\frac{H^{\ast }(10)}{D}$ 从 0.0013 变化到 0.242 mSv/Gy。准直时，$\frac{H^{\ast }(10)}{D}$ 从 0.017 变化到 3.23 mSv/Gy。结果表明，使用物理准直器会使次级中子剂量增加十倍。尽管如此，它仍将低于传统被动散射质子束产生的中子剂量，并与之相当。
