鼻咽癌调强放疗和常规放疗受照剂量对比分析

目的研究鼻咽癌常规放疗和调强放疗(IMRT)受照剂量的差异。方法用放疗计划系统分别进行鼻咽癌常规放疗和调强放疗计划设计,计算肿瘤量70Gy时正常组织受照剂量一体积直方图和所需照射的总跳数。用X射线能量为6MV的加速器实施放疗计划。根据方野散射线和漏射线剂量率的测量值和总跳数,估算射野外不同距离正常组织所受辐射剂量。结果调强放疗射野内正常组织受照剂量低于28Gy的体积是常规放疗的1．43～1．81倍,而高于35Gy时,受照体积仅为常规放疗的0．73～0．30倍;射野外正常组织所受散射线和漏射线照射剂量的估计值约为常规放疗的2倍。结论鼻咽癌常规放疗与调强放疗相比,正常组织受照剂量和受照体积具有成倍差异,调强放疗漏射线和散射线是常规放疗的2倍。

Comparison of the irradiation doses for IMRT and conventional radiotherapy in nasopharyngeal carcinoma patients]

OBJECTIVE: To compare the dose difference in irradiation dose between nasopharyngeal cancer patients receiving conventional radiotherapy (CR) and intensity-modulated radiotherapy (IMRT). METHODS: The various IMRT and the CR plans for patients with nasopharyngeal carcinoma were created by a three-dimensional treatment planning system (3D-TPS). The dose-volume histograms (DVH) of normal tissues and the total number of irradiation monitor units (MU) were calculated by 3D-TPS. The treatment was delivered with 6 MV photons using a "step-and-shoot" technique on a linear accelerator. The X-ray leakage and scattered dose (LSD) at the dmax (maximal dose depth) in water were measured by dosimeter and ion chamber. The dose delivered to normal tissue adjacent to the treatment site at a certain distance was estimated by using LSD and the total MU for different radiotherapy methods. RESULTS: To IMRT patients, the volumes of normal tissues receiving the dose less than 28 Gy and higher than 35 Gy were 1.43-1.81 and 0.70-0.30 times those of CR patients respectively. The LSD irradiated that to the IMRT patients was about two times of the CR patients. CONCLUSION: The dose received by normal tissues in IMRT is two times that in CR.