Kumar Sudhir, Srinivasan P, Sharma S D
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai 400094, India.
Appl Radiat Isot. 2010 Jun;68(6):1108-15. doi: 10.1016/j.apradiso.2009.12.037. Epub 2010 Jan 4.
A cylindrical graphite ionization chamber of sensitive volume 1002.4 cm(3) was designed and fabricated at Bhabha Atomic Research Centre (BARC) for use as a reference dosimeter to measure the strength of high dose rate (HDR) (192)Ir brachytherapy sources. The air kerma calibration coefficient (N(K)) of this ionization chamber was estimated analytically using Burlin general cavity theory and by the Monte Carlo method. In the analytical method, calibration coefficients were calculated for each spectral line of an HDR (192)Ir source and the weighted mean was taken as N(K). In the Monte Carlo method, the geometry of the measurement setup and physics related input data of the HDR (192)Ir source and the surrounding material were simulated using the Monte Carlo N-particle code. The total photon energy fluence was used to arrive at the reference air kerma rate (RAKR) using mass energy absorption coefficients. The energy deposition rates were used to simulate the value of charge rate in the ionization chamber and N(K) was determined. The Monte Carlo calculated N(K) agreed within 1.77 % of that obtained using the analytical method. The experimentally determined RAKR of HDR (192)Ir sources, using this reference ionization chamber by applying the analytically estimated N(K), was found to be in agreement with the vendor quoted RAKR within 1.43%.
巴巴原子研究中心（BARC）设计并制造了一个灵敏体积为1002.4立方厘米的圆柱形石墨电离室，用作参考剂量计，以测量高剂量率（HDR）铱-192近距离治疗源的强度。使用伯林通用腔理论和蒙特卡罗方法，对该电离室的空气比释动能校准系数（N(K)）进行了分析估算。在分析方法中，针对HDR铱-192源的每条谱线计算校准系数，并将加权平均值作为N(K)。在蒙特卡罗方法中，使用蒙特卡罗N粒子代码模拟了测量装置的几何结构以及HDR铱-192源和周围材料的物理相关输入数据。利用质能吸收系数，通过总光子能量注量得出参考空气比释动能率（RAKR）。利用能量沉积率模拟电离室内的电荷率值，并确定N(K)。蒙特卡罗方法计算得到的N(K)与使用分析方法得到的结果在1.77%的范围内一致。使用该参考电离室，通过应用分析估算的N(K)，实验测定的HDR铱-192源的RAKR与供应商报价的RAKR在1.43%的范围内一致。
