DeWerd Larry A, Micka John A, Holmes Shannon M, Bohm Tim D
Department of Medical Physics, University of Wisconsin, Madison, Wisconsin 55106, USA.
Med Phys. 2006 Oct;33(10):3804-13. doi: 10.1118/1.2348765.
A trend is underway toward the use of prepackaged low dose rate brachytherapy sources, which come in the form of strands, coiled line sources, preloaded needles, and sterile cartridge packs. Since the medical physicist is responsible for verification of source strength prior to patient treatment, development of prepackaged source strength verification methods is needed. Existing guidelines are reviewed to establish the situation that medical physicists find with respect to prepackaged sources. This investigation presents an experimental evaluation of the effect of some of these multiseed geometries on source strength measurements. Multiseed strands and coils, whether 125I, 103Pd, or 192Ir can be measured in a chamber with a long, sensitive axial length with a uniform response. Sterile seed cartridge packs can also be measured but require a correction factor to be applied. Sources in needles, however, cannot be measured in the needle since there is too great a variation in needle composition and needle tolerance thickness. Removing these seeds from the needle into a sterile measurement insert, which maintains sterility is a practical source strength verification method, similar to those done for multiple seed configurations in a well chamber with adequate axial uniformity. Values are compared with individual air kerma strength calibrations, and correction factors, are presented' where needed. In each case, care must be taken to maintain sterility as multiple seeds are measured in well chamber inserts.
目前正在出现一种使用预包装低剂量率近距离放射治疗源的趋势，这些源有丝状、盘绕线状源、预装针和无菌盒式包装等形式。由于医学物理师在患者治疗前负责验证源强度，因此需要开发预包装源强度验证方法。对现有指南进行了审查，以确定医学物理师在预包装源方面的情况。本研究对其中一些多籽源几何形状对源强度测量的影响进行了实验评估。无论是125I、103Pd还是192Ir的多籽丝和线圈，都可以在具有长且灵敏轴向长度且响应均匀的电离室中进行测量。无菌籽盒式包装也可以测量，但需要应用校正因子。然而，针中的源无法在针内进行测量，因为针的成分变化太大。将这些籽从针中取出放入保持无菌的测量插入物中，这是一种实用的源强度验证方法，类似于在轴向均匀性良好的电离室中对多种籽配置所做的方法。将测量值与单个空气比释动能强度校准值进行比较，并在需要时给出校正因子。在每种情况下，在电离室插入物中测量多个籽时都必须注意保持无菌。
