Watanabe Y, Roy J, Harrington P J, Anderson L L
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Med Phys. 1998 May;25(5):736-45. doi: 10.1118/1.598255.
We have performed extensive computational and experimental dosimetry of the Henschke applicator with respect to high dose-rate 192Ir brachytherapy using a GAMMAMED remote afterloader. Our goal was to generate clinically useful two- and three-dimensional look-up tables. Dose measurements of the Henschke applicator involved using TLD chips placed in a polystyrene phantom. Monte Carlo simulations were performed using the MCNP code. The computational models included the detailed geometry of 192Ir source, tandem tube, and shielded ovoid. The measured dose rates were corrected for the dependence of TLD sensitivity on the distance of measurement points from the source. Transit dose delivered during source extension to and retraction from a given dwell position was estimated by Monte Carlo simulations, and a correction was applied to the experimental values. For the applicator tandem, the ratio of dose rates obtained by MCNP to those measured by TLD chips ranges from 0.92 to 1.10 with an average of 0.98 and a standard deviation of 0.02. The measured and calculated dose rates at 1 cm on the transverse axis are 1.10 cGy U-1 h-1. For the shielded ovoid, the ratio ranges from 0.88 to 1.16 with an average of 1.00 and a standard deviation of 0.07. Causes of the discrepancy between the Monte Carlo and TLD results were identified. We found that the combined uncertainty of measured dose rates due to these causes is 5.6% for the applicator tandem and 8.4% for the shielded ovoid. Therefore, the results of the Monte Carlo simulation are considered to have been validated by the measurements within the uncertainty involved in the calculation and measurements.
我们使用GAMMAMED遥控后装治疗机，针对高剂量率192铱近距离治疗，对亨施克施源器进行了广泛的计算和实验剂量测定。我们的目标是生成临床上有用的二维和三维查找表。亨施克施源器的剂量测量涉及使用置于聚苯乙烯模体中的热释光剂量计芯片。使用MCNP代码进行了蒙特卡罗模拟。计算模型包括192铱源、串联管和屏蔽卵形体的详细几何结构。对测量的剂量率进行了校正，以考虑热释光剂量计灵敏度对测量点与源距离的依赖性。通过蒙特卡罗模拟估算了源延伸至给定驻留位置和从该位置缩回期间传递的通过剂量，并对实验值进行了校正。对于施源器串联部分，MCNP获得的剂量率与热释光剂量计芯片测量的剂量率之比在0.92至1.10之间，平均为0.98，标准差为0.02。横轴上1 cm处测量和计算的剂量率为1.10 cGy U-1 h-1。对于屏蔽卵形体，该比值在0.88至1.16之间，平均为1.00，标准差为0.07。确定了蒙特卡罗模拟结果与热释光剂量计结果之间差异的原因。我们发现，由于这些原因，施源器串联部分测量剂量率的综合不确定度为5.6%，屏蔽卵形体为8.4%。因此，在计算和测量所涉及的不确定度范围内，蒙特卡罗模拟结果被认为已通过测量得到验证。
