Patel N S, Chiu-Tsao S T, Williamson J F, Fan P, Duckworth T, Shasha D, Harrison L B
Department of Radiation Oncology, Beth Israel Medical Center, New York, New York 10003, USA.
Med Phys. 2001 Aug;28(8):1761-9. doi: 10.1118/1.1388218.
As the efficacy of brachytherapy prostate treatment is becoming realized, new models of 125I seeds are being introduced. In this article we present thermoluminescent dosimetry (TLD) in a solid water phantom for a new design of 125I seed (UroMed/Bebig Symmetra, Model I25.S06). TLD cubes, LiF TLD-100, from Bicron (Solon, OH) with dimension 1 x 1 x 1 mm3 were irradiated at various distances from the seed at angles ranging from 0 degrees to 90 degrees in 10 degrees increments. The TLD detectors were calibrated by irradiation in a 60Co teletherapy beam. Monte Carlo simulation was used to account for TLD energy dependence and the deviation of solid water composition (as determined by chemical analysis of a sample) from liquid water. Dose rates per unit air kerma strength were determined based on calibrations traceable to the 1999 NIST standard (corrected for NIST measurement errors made in 1999) for the Symmetra seed. Dose data is presented in TG-43 format as a function of distance and angle. Values for lambda, F(r, theta), g(r), and the anisotropy constant are obtained for use in radiation treatment planning (RTP) software. The dose rate constant was determined to be 1.033+/-6.4% cGy h(-1) U(-1), which is comparable to model 6702 and higher than model 6711. We find the relative dose distributions of the Symmetra seed are similar to model 6702, and less anisotropic than model 6711. After accounting for deviation of measured solid water composition from the manufacturer's specification, good agreement between TLD results and Monte-Carlo-aided values was found.
随着近距离放射疗法治疗前列腺的疗效逐渐得到认可，新型的125I种子源不断推出。在本文中，我们展示了在固体水模体中对一种新型125I种子源（UroMed/Bebig Symmetra，型号I25.S06）进行热释光剂量测定（TLD）的情况。来自Bicron（俄亥俄州索伦）的尺寸为1×1×1 mm3的TLD立方体LiF TLD - 100，在距离种子源不同距离处，以0度至90度的角度、10度增量进行照射。TLD探测器通过在60Co远距离治疗束中照射进行校准。使用蒙特卡罗模拟来考虑TLD的能量依赖性以及固体水成分（通过样品化学分析确定）与液态水的偏差。基于可追溯到1999年NIST标准（校正了1999年NIST测量误差）的校准，确定了Symmetra种子源每单位空气比释动能强度的剂量率。剂量数据以TG - 43格式呈现为距离和角度的函数。获得了用于放射治疗计划（RTP）软件的λ、F(r,θ)、g(r)和各向异性常数的值。剂量率常数确定为1.033±6.4% cGy h(-1) U(-1)，这与6702型号相当且高于6711型号。我们发现Symmetra种子源相对剂量分布与6702型号相似，且各向异性比6711型号小。在考虑测量的固体水成分与制造商规格的偏差后，发现TLD结果与蒙特卡罗辅助值之间具有良好的一致性。
