Clinical implementation of AAPM Task Group 32 recommendations on brachytherapy source strength specification.
Clinical implementation of AAPM Task Group 32 recommendations on brachytherapy source strength specification.
复制标题
AAPM 任务组 32 关于近距离放射治疗源强度规范建议的临床实施。
作者：
Williamson,JF;Nath,R
历史上，密封近距离放射治疗源的强度由许多物理量描述，包括真放射性、表观放射性和镭的等效质量。最近，AAPM第32工作组建议用一个单位为μ戈伊m2 h −1的单一量空气比释动能强度来代替这些量。已经开发了一组方程，用于明确地将源强度估计值和已公布的剂量率表（假设传统的量和单位）重新归一化为与空气比释动能强度一致的形式。对于常用的近距离放射治疗源，给出了每个源强度形式和单位集的乘法转换因子。要将镭的等效质量转换为空气比释动能强度，需要一个适用于所有源的乘法因子7.23 μ戈伊m2 h −1/mgRaEq。根据对供应商源规范实践的审查，将198 Au、103 Pd和125 I粒子的源强度从表观mCi转换为空气比释动能强度的系数分别为2.06、1.29和1.27 μ戈伊m2 h −1/mCi（表观）。这些因素与光源几何形状无关，但取决于供应商选择的标称曝光率常数值。适用于镭质量或真实活度的换算系数取决于放射源的几何形状和放射性核素特性。由于这些转换因子中的许多取决于供应商对物理常数和暴露速率常数的选择，因此提醒读者在临床上采用这些值之前仔细审查供应商的源强度规范实践。最后，阐明了各种源强量与源周围介质吸收剂量率之间的关系。
Historically the strength of sealed brachytherapy sources has been described by many physical quantities, including true activity, apparent activity, and equivalent mass of radium. Recently, the AAPM Task Group 32 recommended that these quantities be replaced by a single quantity, air‐kerma strength, with units of μGy m2h−1. A set of equations has been developed for unambiguously converting source strength estimates and renormalizing published dose‐rate tables, which assume traditional quantities and units, into forms consistent with air‐kerma strength. For commonly used brachytherapy sources, multiplicative conversion factors for each source‐strength formalism and set of units are given. To convert equivalent mass of radium to air‐kerma strength requires a single multiplicative factor, 7.23 μGy m2h−1/mgRaEq, applicable to all sources. Based upon a review of vendor source specification practices, the factors for converting source strength of198Au,103Pd, and125I seeds from apparent mCi to air‐kerma strength are 2.06, 1.29, and 1.27 μGy m2h−1/mCi(apparent), respectively. These factors are independent of source geometry but depend on the nominal exposure rate constant value selected by the vendor. Conversion factors applicable to mass of radium or true activity depend upon both source geometry and radionuclide identity. Because many of these conversion factors depend upon vendor choices of physical constants and exposure rate constants, readers are cautioned to carefully review vendor source strength specification practices before adopting these values clinically. Finally, the relationships between the various source strength quantities and absorbed dose rate in the medium surrounding the source are elucidated.