摘要
目的 探讨电子束照射野挡块对中心轴剂量和输出因子的影响。方法 用瑞典Sca ditronix公司生产的RFA 30 0型三维水箱及P型硅半导体探头对瓦里安 2 10 0C和 2 30 0C/D直线加速器的多种能量电子束进行了中心轴百分深度剂量 (PDD)扫描 ,并测量了照射野输出因子。结果 测得的PDD数据表明 ,电子束深度剂量对照射野铅挡大小有某种程度的依赖性 ,一般倾向是当照射野减小时表面剂量增大 ,治疗深度减小 ,最大剂量深度 (R10 0 )向表面移。这些变化在高能时最为明显。输出因子的测量结果说明 ,对不同能量电子束在不同限光筒条件下 ,输出因子随照射野铅挡大小改变的情况不尽相同。结论 临床治疗时使用的限光筒大小要尽量与实际照射野面积接近 ,在使用铅挡构成很小的照射野 (如 <6cm× 6cm)时 ,应实际测量输出因子 。
Objective Clinical application of electrons often involves some beam in which the field size varies with the applicators. The work was done to understand the electron beam characteristics in different field sizes. Methods Percent depth dose and the dose output factor were measured for square and rectangular fields at 100?cm source to surface distance ( SSD ) . Central axis percent depth dose (PDD) measurements were made using the RFA 300 three dimensional radiation field analyzer with a shielded p type diode detector . The dose output factors were measured with the RFA 300 three dimensional radiation field analyzer with a PTW 0.1?cm 3 chamber and a Farmer 2570/1 dosimeter with a 2571 ion chamber in a water phantom. Results The measurements showed that the depth dose curves and the output factors were sometimes dependent on how the field sizes were formed. The change in depth dose with field size was more pronounced in the high energy beams than the low energy ones. However, the output factor did not show any systematic energy dependence because each applicator had it's own X ray jaw setting at each energy. Conclusions When using small inserted apertures to treat small lesions, we should verify the conformation of depth dose and output factors. In this case, we should use applicator dependent output factors at each energy to calculate the monitor units for irradiation.
出处
《中华放射肿瘤学杂志》
CSCD
北大核心
2001年第3期197-199,共3页
Chinese Journal of Radiation Oncology