Subhalaxmi Mishra, Palani Selvam T
Radiological Physics and Advisory Division, Health, Safety and Environment Group, Bhabha Atomic Research Centre, Mumbai, 400 094, Maharashtra, India,
Radiol Phys Technol. 2015 Jul;8(2):215-23. doi: 10.1007/s12194-015-0310-9. Epub 2015 Mar 10.
Our aim in this study was to calculate Monte Carlo-based phantom scatter corrections of various radiochromic films for different solid phantoms for high-energy brachytherapy sources. Brachytherapy sources (60)Co, (137)Cs, (192)Ir, and (169)Yb and radiochromic films EBT, EBT2 (lot 020609 and lot 031109), RTQA, XRT, XRQA, and HS were investigated in this study. The solid phantom materials investigated were PMMA (polymethylmethacrylate), polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. Monte Carlo-based user codes DOSRZnrc and FLURZnrc of the EGSnrc code system were employed in the present work. For the (60)Co source, the polystyrene, plastic water, solid water, virtual water, RW1, RW3, and WE210 phantoms were water equivalent for the investigated films, but showed distance-dependent values for XRT and XRQA films. For the (137)Cs and (192)Ir sources, the solid water, virtual water, RW1, RW3, and WE210 phantoms were water equivalent for the investigated films, but showed distance-dependent values for XRT and XRQA films. For these sources, the remaining phantoms showed distance-dependent values for all of the films investigated. For the (169)Yb source, all of the investigated phantoms showed distance-dependent values for the investigated films. This study suggests that radiochromic films demonstrate distance-dependent values, but the degree of dependence is related to the types of solid phantom and film. Hence, for brachytherapy dosimetry involving radiochromic films and solid phantom materials, phantom scatter corrections need to be applied.
本研究的目的是针对高能近距离放射治疗源，计算不同固体模体的各种放射变色胶片基于蒙特卡洛方法的模体散射校正。本研究调查了近距离放射治疗源（60）Co、（137）Cs、（192）Ir和（169）Yb以及放射变色胶片EBT、EBT2（批号020609和批号031109）、RTQA、XRT、XRQA和HS。所研究的固体模体材料有聚甲基丙烯酸甲酯（PMMA）、聚苯乙烯、固体水、虚拟水、塑料水、RW1、RW3、A150和WE210。本工作采用了EGSnrc代码系统中基于蒙特卡洛方法的用户代码DOSRZnrc和FLURZnrc。对于（60）Co源，聚苯乙烯、塑料水、固体水、虚拟水、RW1、RW3和WE210模体对于所研究的胶片是水等效的，但对于XRT和XRQA胶片显示出距离依赖性值。对于（137）Cs和（192）Ir源，固体水、虚拟水、RW1、RW3和WE210模体对于所研究的胶片是水等效的，但对于XRT和XRQA胶片显示出距离依赖性值。对于这些源，其余模体对于所有所研究的胶片都显示出距离依赖性值。对于（169）Yb源，所有所研究的模体对于所研究的胶片都显示出距离依赖性值。本研究表明，放射变色胶片显示出距离依赖性值，但依赖程度与固体模体和胶片的类型有关。因此，对于涉及放射变色胶片和固体模体材料的近距离放射治疗剂量测定，需要应用模体散射校正。
