Brady Samuel L, Toncheva Greta, Dewhirst Mark W, Yoshizumi Terry T
Medical Physics Graduate Program, Duke University, Durham, NC 27705, USA.
Health Phys. 2009 Sep;97(3):195-205. doi: 10.1097/HP.0b013e3181a9bd42.
To provide for accurate dosimetry in a 137Cs irradiator, the following were investigated: (1) correct mapping of the irradiator cavity's dose distribution, (2) rotated versus stationary dose rate measurements, (3) exposure-to-dose calibration selection for exposure time calculation, and (4) irradiator-timer error correction. This work introduces techniques to map dose distributions and measure dose rates with new high-sensitivity radiochromic films and a small-volume ion chamber constructed for in-beam, high-intensity gamma irradiation. Measured film distributions were compared to manufacturer-provided data and independent measurements from an ion chamber and TLD-100 chips. Measured film distributions agreed with the manufacturer-provided data in the central-vertical region, but disagreed by as much as 95% in surrounding regions. The independent measurements agreed within 96% with the measured dose distribution. Dose rates varied by approximately 11% for a rotational versus stationary setup, by approximately 10% for the dose-to-medium correction between air and soft tissue, and by approximately 4-12% for irradiation times from 0.2-0.7 min due to timer error. In conclusion, a critical irradiator characterization should be performed, initially, as a part of the acceptance testing of a newly installed irradiator, and periodically as an ongoing quality assurance protocol. We investigated, and recommend as part of a comprehensive irradiator verification protocol, the inclusion of radiochromic film-measured dose distributions, dose rates measured during rotation when samples are likewise rotated for exposure, timer error corrections for short-time irradiation, and exposure-to-dose corrections that reflect typical sample compositions, e.g., soft tissue or air.
为了在137Cs辐照器中实现准确的剂量测定，对以下内容进行了研究：(1) 辐照器腔室剂量分布的正确映射；(2) 旋转与固定状态下的剂量率测量；(3) 用于曝光时间计算的曝光-剂量校准选择；(4) 辐照器定时器误差校正。本研究介绍了利用新型高灵敏度放射变色薄膜和为束内高强度伽马辐照构建的小体积电离室来映射剂量分布和测量剂量率的技术。将测量得到的薄膜分布与制造商提供的数据以及来自电离室和TLD-100芯片的独立测量结果进行了比较。测量得到的薄膜分布在中心垂直区域与制造商提供的数据一致，但在周边区域相差高达95%。独立测量结果与测量得到的剂量分布在96%的范围内一致。旋转与固定设置下的剂量率变化约为11%，空气与软组织之间的剂量-介质校正导致的剂量率变化约为10%，由于定时器误差，0.2 - 0.7分钟辐照时间的剂量率变化约为4 - 12%。总之，关键的辐照器特性描述应首先作为新安装辐照器验收测试的一部分进行，并且作为持续质量保证协议定期进行。我们进行了研究，并建议作为全面辐照器验证协议的一部分，纳入放射变色薄膜测量的剂量分布、样品旋转曝光时旋转过程中测量的剂量率、短时间辐照的定时器误差校正以及反映典型样品组成（如软组织或空气）的曝光-剂量校正。
