Carolan M, Dao P, Fox C, Metcalfe P
Illawarra Cancer Care Centre, Wollongong, New South Wales, Australia.
Australas Radiol. 2000 Aug;44(3):290-5. doi: 10.1046/j.1440-1673.2000.00816.x.
A small but growing proportion of patients requiring radiotherapy for prostate cancer have one or two hip prostheses which may shadow the target and affect the dose distribution. Approximately 10 such patients are treated at the Illawarra Cancer Care Centre per year. Hence a study was undertaken to examine the accuracy of various treatment methods that involve some of the treatment fields travelling through the prosthesis. A fixed-field measurement showed a dose reduction of 52% in the shadow of the prosthesis. A Monte Carlo simulation confirmed an increase in dose on the distal surface of the prosthesis of 35%. Of more clinical relevance, however, is the dose distribution due to the overall combined field treatment. Using a power law correction benchmarked against thermoluminescent dosimeters and Gafchromic film, three different beam set-ups for patient treatment were planned and the dose variation analysed. A four-field brick technique gave a dose variation across the target volume of +/- 15% whereas a dual arc technique gave a dose variation of only +/- 5%. A four-field oblique technique gave a dose variation of only +/- 2% across the target volume but the oblique field technique included extra dose to the rectum.
一小部分但比例不断增加的前列腺癌放疗患者体内有一两个髋关节假体，这可能会遮挡靶区并影响剂量分布。每年约有10名此类患者在伊拉瓦拉癌症护理中心接受治疗。因此，开展了一项研究，以检验各种治疗方法的准确性，这些治疗方法涉及部分治疗射野穿过假体。固定野测量显示，假体阴影处剂量降低了52%。蒙特卡罗模拟证实，假体远端表面剂量增加了35%。然而，更具临床相关性的是整体联合野治疗导致的剂量分布。采用以热释光剂量计和放射变色薄膜为基准的幂律校正方法，规划了三种不同的患者治疗射束设置，并分析了剂量变化。四野方形技术在靶区内产生的剂量变化为±15%，而双弧技术产生的剂量变化仅为±5%。四野斜野技术在靶区内产生的剂量变化仅为±2%，但斜野技术会使直肠接受额外剂量。
