蜡块和真空固定膜对皮肤剂量影响的研究

Relative skin dose contamination by wax or vac lok cushion

目的 定量研究蜡块和真空固定膜对入射面及出射面处皮肤剂量及靶区剂量的影响。并对所谓的“皮肤超剂量”现象进行了探讨。方法 使用10 MV X 射线;国产可抽真空型塑料固定膜;丙烯酸脂类蜡模;半导体探头;DPD- 510 半导体现场测量仪及γ剂量仪( Farmer 2570/1 剂量仪,2581 电离室) 。采用源轴距离(SAD)和源皮距离(SSD) 方法。测量时塑料固定膜和蜡块均紧贴体模表面。结果 国产可抽真空型塑料固定膜对建成区剂量的影响较大,在皮肤下2 m m 处,可增高23.8% (5cm ×5cm) 和16 .9% (20 cm ×20cm) 。对最大剂量点的剂量影响约增高0 .3% 。对出射面的剂量测量显示, 放与不放真空固定膜时测量结果之均值完全相同。作为组织补偿用的蜡块对皮肤剂量并不造成除可计算的百分深度剂量( PDD) 增高而引起的剂量升高外的剂量增加。结论 国产可抽真空型塑料固定膜对最大点剂量和靶区剂量及出射面剂量无影响,而对入射面建成区剂量的影响较大, 射野越小影响越大。患者表面皮肤的放射反应可能是由于表面皮肤剂量因PDD

Objective To study how much the relative skin dose is changed with the application of wax and vac lok cushion made in Shanghai.Methods Using 10 MV X ray, vac lok cushion, wax, semiconductor detector ( scanditronix DPD 510) and Farmer 2570/1 dosimeter, SAD and SSD method were followed in skin dose measurement. Results There was a heavy dose contamination under the vac lok cushion. A 23.8%(5?cm×5?cm) and 16.9%(20?cm×20?cm) dose increase was found 2?mm beneath the surface. And this effect varied with the field size. The smaller the field size, the more increase in the relative dose. Wax,as a bolus,dose not cause any additional dose increase at a depth of 2?mm beneath the surface except that due to the calculable percentage depth dose (PDD) as compared with the theoretical results. Conclusions The home made voc lok cushion exerts no influence on the point of maximum dose,target dose or dose on the exit beam. But,its influence on the build up range beneath the entry beam is relatively large. The smaller the portal, the larger the influence. The increase of skin reaction may be due to the elevation of PDD. Wax,as a bolus,does not cause any additional dose increas at a depth of 2?mm beneath the surface except that due to the calculable percentage depth dose(PDD).