Unidad de Radiofísica, Hospital Clínico Universitario San Cecilio, E-18016 Granada, Spain.
Servicio de Radiofísica y Protección Radiológica, Hospital Universitario de Gran Canaria Dr. Negrín, E-35010 Las Palmas de Gran Canaria, Spain.
Phys Med. 2018 Feb;46:109-113. doi: 10.1016/j.ejmp.2018.01.020. Epub 2018 Feb 4.
We studied the dependence on air density of the response of the PTW 34013 ionization chamber, recently upgraded for dosimetry control of low energy X-ray beams.
Measurements were performed by changing the pressure conditions inside a pressure chamber. The behavior of the measurements against the air density inside this chamber was analyzed. X-ray beams generated with 50, 70, 100, 150 and 200 kVp and the two electrometer polarities were considered.
For all beams studied, measurements corrected with the conventional temperature and pressure factor showed a residual dependence on the air density that was described with a linear function of the air density. For the 50 and 70 kVp beams, corrected measurements remained ∼1% smaller than the value found at standard pressure/temperature conditions, for both electrometer polarities and for the air density range typical in clinical conditions. For air densities smaller than the standard one, measurements found for 100, 150 and 200 kVp beams were below or above the value found at standard pressure and temperature when the negative or positive electrometer polarities were used, respectively. The differences with the measurements at standard conditions were less than 1% for the 100 kVp beam and below 4% for the other two beams.
The PTW 34013 ionization chamber showed a dependence on the air density that is not properly described with the usual temperature and pressure correction factor. This residual dependence is negligible for low energy beams, for which this chamber is recommended, but is more substantial for beams with energy above 80 kVp.
我们研究了 PTW 34013 电离室响应对空气密度的依赖性，该电离室最近经过升级，可用于低能 X 射线束的剂量控制。
通过改变压力室内的压力条件进行测量。分析了测量值与该室内空气密度之间的关系。考虑了 50、70、100、150 和 200 kVp 的 X 射线束以及两种静电计极性。
对于所有研究的光束，使用传统的温度和压力修正因子进行修正的测量值仍然存在对空气密度的残余依赖性，该依赖性可用空气密度的线性函数来描述。对于 50 和 70 kVp 束，在两种静电计极性和临床条件下典型的空气密度范围内，修正后的测量值仍然比标准压力/温度条件下的测量值小约 1%。对于小于标准空气密度的情况，当使用负或正静电计极性时，对于 100、150 和 200 kVp 束，测量值分别低于或高于标准压力和温度下的测量值。与标准条件下的测量值相比，对于 100 kVp 束，差异小于 1%，对于其他两个束，差异小于 4%。
PTW 34013 电离室对空气密度的依赖性不能用通常的温度和压力修正因子来正确描述。对于低能束，这种依赖性可以忽略不计，因为该电离室就是为此推荐的，但对于能量高于 80 kVp 的束，这种依赖性就更显著了。
