Fregene A O
Med Phys. 1976;3(5):360-3. doi: 10.1118/1.594267.
The total effects of the cavity displacement and the perturbation of the field by the cavity in thimble-chamber measurements of absorbed dose were investigated for electron beams of energy 15, 20, 30, and 39 MeV and for 60CO gamma radiation by LiF dosimeter rods of diameter 1 mm and length 6 mm. The measurements were carried out in a polystyrene phantom at recommended reference depths and at the respective electronic equilibrium depths, for cavities of varying sizes. Owing to the cavity effect, the ratio of absorbed dose of a 5-mm-diameter cavity to that of a point cavity, at the reference depth, was 1.028 for 60Co gamma radiation; this ratio varied from 1.022 at 15 MeV to 1.033 for 39-MeV electrons. Although the cavity effect is present over regions of the depth dose where dose is constant with depth, here it was less dependent on cavity size than when the cavity was positioned at ICRU depths. Both the displacement and perturbation of the radiation field effects are automatically corrected through the experimental arrangement in this work.
利用直径为1mm、长度为6mm的LiF剂量计棒，对能量为15、20、30和39MeV的电子束以及60Coγ射线，研究了指形电离室吸收剂量测量中腔室位移和腔室对场的微扰的总效应。测量是在聚苯乙烯模体中，在推荐的参考深度和各自的电子平衡深度处，针对不同尺寸的腔室进行的。由于腔室效应，在参考深度处，60Coγ射线直径为5mm的腔室的吸收剂量与点腔室吸收剂量之比为1.028；该比值在15MeV时为1.022，在39MeV电子束时为1.033。尽管在深度剂量中剂量随深度恒定的区域存在腔室效应，但与腔室位于ICRU深度时相比，此处它对腔室尺寸的依赖性较小。在本工作中，通过实验装置自动校正了辐射场效应的位移和微扰。
