The Regional Medical Physics Department, The James Cook University Hospital, Marton Road, Middlesbrough, TS4 3BW, UK.
Phys Med Biol. 2011 Aug 21;56(16):5397-410. doi: 10.1088/0031-9155/56/16/020. Epub 2011 Jul 29.
This paper details a practical method for deriving the reference air kerma rate calibration coefficient for Farmer NE2571 chambers using the U.K. Institute of Physics and Engineering in Medicine (IPEM) code of practice for the determination of the reference air kerma rate for HDR (192)Ir brachytherapy sources based on the National Physical Laboratory (NPL) air kerma standard. The reference air kerma rate calibration coefficient was derived using pressure, temperature and source decay corrected ionization chamber response measurements over three successive (192)Ir source clinical cycles. A secondary standard instrument (a Standard Imaging 1000 Plus well chamber) and four tertiary standard instruments (one additional Standard Imaging 1000 Plus well chamber and three Farmer NE2571 chambers housed in a perspex phantom) were used to provide traceability to the NPL primary standard and enable comparison of performance between the chambers. Conservative and optimized estimates on the expanded uncertainties (k = 2) associated with chamber response, ion recombination and reference air kerma rate calibration coefficient were determined. This was seen to be 2.3% and 0.4% respectively for chamber response, 0.2% and 0.08% respectively for ion recombination and 2.6% and 1.2% respectively for the calibration coefficient. No significant change in ion recombination with source decay was observed over the duration of clinical use of the respective 192Ir sources.
本文详细介绍了一种实用的方法，用于使用基于国家物理实验室（NPL）空气比释动能标准的英国物理研究所和工程医学学会（IPEM）实践规程，为 HDR（192）Ir 近距离治疗源确定参考空气比释动能率，来推导 Farmer NE2571 腔室的参考空气比释动能率校准系数。该参考空气比释动能率校准系数是通过在三个连续的（192）Ir 源临床周期中，对压力、温度和源衰变校正后的电离室响应测量得出的。使用二级标准仪器（标准成像 1000 加仑井腔）和四个三级标准仪器（一个额外的标准成像 1000 加仑井腔和三个放置在有机玻璃模体中的 Farmer NE2571 腔室），提供与 NPL 一级标准的可追溯性，并能够比较腔室之间的性能。保守和优化的扩展不确定度（k = 2）估计与腔室响应、离子复合和参考空气比释动能率校准系数相关联。对于腔室响应，分别为 2.3%和 0.4%；对于离子复合，分别为 0.2%和 0.08%；对于校准系数，分别为 2.6%和 1.2%。在相应的 192Ir 源临床使用期间，没有观察到离子复合随源衰变而发生显著变化。
