Lazarus Graeme L, van Eeden Déte, du Plessis Frederik Cp
University of Kwazulu-Natal, School of Clinical Medicine, College of Health Sciences, Durban, 4013, South Africa.
Department of Medical Physics, University of the Free State, Bloemfontein, 9300, South Africa.
Heliyon. 2022 Sep 19;8(9):e10682. doi: 10.1016/j.heliyon.2022.e10682. eCollection 2022 Sep.
In Intra-Operative Radiation Therapy (IORT) the tumour site is surgically exposed and normal tissue located around the tumour may be avoided. Electron applicators would require large surgical incisions; therefore, the preferred mechanism for beam collimation is the IORT cone system. FLASH radiotherapy (FLASH-RT) involves the treatment of tumours at ultra-high dose rates and the IORT cone system can also be used. This study validates the Monte Carlo-based calculations for these small electron beams to accurately determine the dose characteristics of each possible cone-energy combination as well as custom-built alloy cutouts attached to the end of the IORT cone. This will contribute to accurate dose distribution and output factor calculations that are essential to all radiation therapy treatments. A Monte Carlo (MC) model was modelled for electron beams produced by a Siemens Primus LINAC and the IORT cones. The accelerator was built with the component modules available in the BEAMnrc code. The phase-space file generated by the BEAM simulation was used as the source input for the subsequent DOSXYZnrc simulations. Percentage Depth Dose (PDD) data and profiles were extracted from the dose distributions obtained with the DOSXYZnrc simulations. These beam characteristics were compared with measured data for 6, 12, and 18 MeV electron beams for the IORT open cones of diameters 19, 45, and 64 mm and irregularly shaped cutouts. The MC simulations could replicate electron beams within a criterion of 3%/3 mm. Applicator factors were within 0.7%, and cone factors showed good agreement, except for the 9 mm cone size. Based on the successful comparisons between measurement and MC-calculated dose distributions, output factors for the open cones and for small irregularly shaped IORT beams, it may be concluded that the Monte Carlo based dose calculation could replicate electron beams used for IORT and FLASH-IORT.
在术中放射治疗（IORT）中，肿瘤部位通过手术暴露，可避免肿瘤周围的正常组织。电子施源器需要较大的手术切口；因此，束流准直的首选机制是IORT锥形系统。FLASH放射治疗（FLASH-RT）涉及以超高剂量率治疗肿瘤，也可使用IORT锥形系统。本研究验证了基于蒙特卡罗方法对这些小电子束的计算，以准确确定每种可能的锥形-能量组合以及连接到IORT锥形末端的定制合金挡块的剂量特性。这将有助于进行准确的剂量分布和输出因子计算，而这对于所有放射治疗都是至关重要的。针对西门子Primus直线加速器产生的电子束和IORT锥形系统建立了蒙特卡罗（MC）模型。加速器是用BEAMnrc代码中的组件模块构建的。BEAM模拟生成的相空间文件用作后续DOSXYZnrc模拟的源输入。从DOSXYZnrc模拟获得的剂量分布中提取百分深度剂量（PDD）数据和剂量分布图。将这些束流特性与直径为19、45和64 mm的IORT开放锥形以及不规则形状挡块的6、12和18 MeV电子束的测量数据进行比较。MC模拟能够在3%/3 mm的标准范围内复制电子束。施源器因子在0.7%以内，除9 mm锥形尺寸外，锥形因子显示出良好的一致性。基于测量值与MC计算的剂量分布、开放锥形和小的不规则形状IORT束的输出因子之间的成功比较，可以得出结论，基于蒙特卡罗的剂量计算能够复制用于IORT和FLASH-IORT的电子束。
