An experimental and computational investigation of the standard temperature-pressure correction factor for ion chambers in kilovoltage x rays
An experimental and computational investigation of the standard temperature-pressure correction factor for ion chambers in kilovoltage x rays
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DOI：
10.1118/1.2799580
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发表时间：
2007-12-01
期刊：
影响因子：
3.8
通讯作者：
Rogers, D. W. O.
中科院分区：
文献类型：
--
作者：
La Russa, Daniel J.;McEwen, Malcolm;Rogers, D. W. O.
对于腔体与周围大气相通的离子室，在给定温度和压力下测量的响应必须使用标准温度-压力校正因子（P-TP）进行校正。以前的论文完全基于蒙特卡罗模拟[D. J. La Russa和D. W. O. Rogers，Med.Phys.33，4590-4599（2006）]指出了P-TP校正因子在用于校正非空气等效室对低能X射线束的响应时的缺点。这项工作提出了几个实验的结果，证实了这些计算的一些离子室。Monte Carlo模拟的实验装置揭示了额外的洞察力的各种因素影响的P-TP的击穿的程度，包括杂质和腔室尺寸的敏感性的影响。对于未过滤的60 kV射束，在0.7 atm下测量的NE 2571离子室的P-TP校正响应比在参考条件下测量的响应低2.5%。在一般情况下，使用EGSnrc的实验设置的蒙特卡罗模拟的测量值的0.5%以内。EGSnrc计算值的空气比释动能校准系数（N-K）在低X射线能量也提供了作为一种手段，估计在调查室的杂质水平。获得了三个腔室的N-K计算值（标准化为250 kV射束的测量值），并且在实验的1%范围内，只有一个例外，Exradin A12在50 kV射束中。(C)2007年美国医学物理学家协会。
For ion chambers with cavities open to the surrounding atmosphere, the response measured at a given temperature and pressure must be corrected using the standard temperature-pressure correction factor (P-TP). A previous paper based solely on Monte Carlo simulations [D. J. La Russa and D. W. O. Rogers, Med. Phys. 33, 4590-4599 (2006)] pointed out the shortcomings of the P-TP correction factor when used to correct the response of non-air-equivalent chambers for low-energy x-ray beams. This work presents the results of several experiments that corroborate these calculations for a number of ion chambers. Monte Carlo simulations of the experimental setup revealed additional insight into the various factors affecting the extent of the breakdown of P-TP, including the effect of impurities and the sensitivity to chamber dimensions. For an unfiltered 60 kV beam, the P-TP-corrected response of an NE 2571 ion chamber measured at 0.7 atm was 2.5% below the response measured at reference conditions. In general, Monte Carlo simulations of the experimental setup using EGSnrc were within 0.5% of measured values. EGSnrc-calculated values of air kerma calibration coefficients (N-K) at low x-ray energies are also provided as a means of estimating the level of impurities in the chambers investigated. Calculated values of N-K normalized to the value measured for a 250 kV beam were obtained for three chambers and were within 1% of experiment with one exception, the Exradin A12 in a 50 kV beam. (C) 2007 American Association of Physicists in Medicine.