Dept. Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia.
J Appl Clin Med Phys. 2013 Jan 7;14(1):4037. doi: 10.1120/jacmp.v14i1.4037.
For the purpose of dose measurement using a high-dose rate (192)Ir source, four methods of thermoluminescent dosimeter (TLD) calibration were investigated. Three of the four calibration methods used the (192)Ir source. Dwell times were calculated to deliver 1 Gy to the TLDs irradiated either in air or water. Dwell time calculations were confirmed by direct measurement using an ionization chamber. The fourth method of calibration used 6 MV photons from a medical linear accelerator, and an energy correction factor was applied to account for the difference in sensitivity of the TLDs in (192)Ir and 6 MV. The results of the four TLD calibration methods are presented in terms of the results of a brachytherapy audit where seven Australian centers irradiated three sets of TLDs in a water phantom. The results were in agreement within estimated uncertainties when the TLDs were calibrated with the (192)Ir source. Calibrating TLDs in a phantom similar to that used for the audit proved to be the most practical method and provided the greatest confidence in measured dose. When calibrated using 6 MV photons, the TLD results were consistently higher than the (192)Ir-calibrated TLDs, suggesting this method does not fully correct for the response of the TLDs when irradiated in the audit phantom.
为了使用高剂量率（192）Ir 源进行剂量测量，研究了四种热释光剂量计（TLD）校准方法。这四种校准方法中的三种使用了（192）Ir 源。通过 dwell time 计算，将 1 Gy 的剂量递送至在空气中或水中辐照的 TLD。通过使用电离室进行直接测量，验证了 dwell time 计算。第四种校准方法使用了来自医用直线加速器的 6 MV 光子，并应用能量校正因子来考虑 TLD 在（192）Ir 和 6 MV 中的灵敏度差异。将这四种 TLD 校准方法的结果呈现为七个澳大利亚中心在水模体中辐照三组 TLD 的近距离治疗审核的结果。当使用（192）Ir 源对 TLD 进行校准时，结果在估计的不确定度内一致。在类似于审核中使用的水模体中校准 TLD 被证明是最实用的方法，并为测量剂量提供了最大的信心。当使用 6 MV 光子进行校准时，TLD 的结果始终高于（192）Ir 校准的 TLD，这表明该方法不能完全校正 TLD 在审核水模体中辐照时的响应。
