Department of Physics, Clatterbridge Cancer Centre, Clatterbridge Road, Bebington Wirral, UK.
Phys Med Biol. 2012 Jul 21;57(14):4461-76. doi: 10.1088/0031-9155/57/14/4461. Epub 2012 Jun 22.
The impact of density and atomic composition on the dosimetric response of various detectors in small photon radiation fields is characterized using a 'density-correction' factor, F(detector), defined as the ratio of Monte Carlo calculated doses delivered to water and detector voxels located on-axis, 5 cm deep in a water phantom with a SSD of 100 cm. The variation of F(detector) with field size has been computed for detector voxels of various materials and densities. For ion chambers and solid-state detectors, the well-known variation of F(detector) at small field sizes is shown to be due to differences between the densities of detector active volumes and water, rather than differences in atomic number. However, associated changes in the measured shapes of small-field profiles offset these variations in F(detector), so that integral doses measured using the different detectors are quite similar, at least for slit fields. Since changes in F(detector) with field size arise primarily from differences between the densities of the detector materials and water, ideal small-field relative dosimeters should have small active volumes and water-like density.
使用“密度校正”因子 F(detector) 来描述密度和原子组成对小光子辐射场中各种探测器剂量响应的影响，该因子定义为在水模中 SSD 为 100cm 时，位于水和探测器体素轴上 5cm 深处的蒙特卡罗计算剂量与探测器体素的比值。已经计算了不同材料和密度的探测器体素的 F(detector) 随射野大小的变化。对于电离室和固态探测器，小射野尺寸下 F(detector) 的众所周知的变化是由于探测器有效体积和水的密度差异，而不是原子数的差异。然而，小射野轮廓的测量形状的相关变化抵消了 F(detector) 的这些变化，因此使用不同探测器测量的积分剂量非常相似，至少对于狭缝射野是如此。由于 F(detector) 随射野大小的变化主要源于探测器材料和水的密度差异，因此理想的小射野相对剂量计应该具有小的有效体积和水的密度。
