Ghorbani Mahdi, Khajetash Benyamin, Ghatei Najmeh, Mehrpouyan Mohammad, Meigooni Ali S, Shahraini Ramin
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Tehran, Iran.
Radiol Oncol. 2017 Feb 22;51(1):101-112. doi: 10.1515/raon-2017-0009. eCollection 2017 Mar 1.
Interstitial rotating shield brachytherapy (I-RSBT) is a recently developed method for treatment of prostate cancer. In the present study TG-43 dosimetric parameters of a Gd source were obtained for use in I-RSBT.
A Gd source located inside a needle including a Pt shield and an aluminum window was simulated using MCNPX Monte Carlo code. Dosimetric parameters of this source model, including air kerma strength, dose rate constant, radial dose function and 2D anisotropy function, with and without the shields were calculated according to the TG-43 report.
The air kerma strength was found to be 6.71 U for the non-shielded source with 1 GBq activity. This value was found to be 0.04 U and 6.19 U for the Pt shield and Al window cases, respectively. Dose rate constant for the non-shielded source was found to be 1.20 cGy/(hU). However, for a shielded source with Pt and aluminum window, dose rate constants were found to be 0.07 cGy/(hU) and 0.96 cGy/(hU), on the shielded and window sides, respectively. The values of radial dose function and anisotropy function were tabulated for these sources. Additionally, isodose curves were drawn for sources with and without shield, in order to evaluate the effect of shield on dose distribution.
Existence of the Pt shield may greatly reduce the dose to organs at risk and normal tissues which are located toward the shielded side. The calculated air kerma strength, dose rate constant, radial dose function and 2D anisotropy function data for the Gd source for the non-shielded and the shielded sources can be used in the treatment planning system (TPS).
间质旋转屏蔽近距离放射疗法（I-RSBT）是一种最近开发的前列腺癌治疗方法。在本研究中，获取了钆源的TG-43剂量学参数，用于I-RSBT。
使用MCNPX蒙特卡罗代码模拟了位于带有铂屏蔽和铝窗的针内的钆源。根据TG-43报告，计算了该源模型在有屏蔽和无屏蔽情况下的剂量学参数，包括空气比释动能强度、剂量率常数、径向剂量函数和二维各向异性函数。
发现活性为1GBq的无屏蔽源的空气比释动能强度为6.71U。对于铂屏蔽和铝窗情况，该值分别为0.04U和6.19U。发现无屏蔽源的剂量率常数为1.20cGy/(hU)。然而，对于带有铂和铝窗的屏蔽源，在屏蔽侧和窗侧的剂量率常数分别为0.07cGy/(hU)和0.96cGy/(hU)。列出了这些源的径向剂量函数和各向异性函数值。此外，绘制了有屏蔽和无屏蔽源的等剂量曲线，以评估屏蔽对剂量分布的影响。
铂屏蔽的存在可大大降低位于屏蔽侧的危及器官和正常组织的剂量。计算得到的无屏蔽和屏蔽钆源的空气比释动能强度、剂量率常数、径向剂量函数和二维各向异性函数数据可用于治疗计划系统（TPS）。
