图像引导鼻咽癌调强放疗摆位误差及剂量学验证研究

摘要

目的:探讨锥形束CT(CBCT)影像引导鼻咽癌调强放疗的摆位误差及建立个体化调强计划剂量验证方法.方法:利用X线千伏锥形束CT对32例鼻咽癌调强放疗患者进行426次治疗前扫描,通过图像融合软件将计划CT与CBCT影像匹配,得到靶区中心的摆位误差,在线修正后,重新扫描得到116次CBCT影像,再匹配后得到修正后靶区偏差;在治疗完成后,重新扫描36次,得到治疗后靶区偏差中心.通过修正固体水模测试和矩阵电离室的参数,可验证高剂量区、低剂量区、中心点、均匀区和高梯度区域的绝对剂量:利用Cama分析得到单野和个体计划的通过评价率.结果:对32例鼻咽癌426次CBCT扫描中,三个方向偏差,X(左右)、Y(上下),Z(前后)分别为(0.44±2.03)mm、(0.51±2.75)mm、(-0.37±2.14)mm;当三个方向大于2 mm时进行位置修正,修正后重新进行CBCT扫描和匹配得到新的三个方向的偏差,X为(0.07±0.59)mm、Y为(0.07±0.80)mm、Z为(-0.02±0.75)mm;治疗完成后再扫描36次,匹配得到的偏差三个方向X、Y、Z分别为(0.19±0.59)mm、(0.15±0.73)mm、(-0.08±0.72)mm;用矩阵电离室验证调强计划相对剂量,对于单野,Camma值为88.2%～99.2%,对于整个计划Gamma值为90.2%～99.7%.绝对剂量验证主要是对等中心点、剂量均匀区、高剂量区、较低剂量区、高梯度区选择5个点进行检测共完成160个点,百分偏差范围为-3.9%～4.2%.结论:通过在线的摆位修正和调强计划的个体化验证,可保证鼻咽癌调强放疗的位置和剂量的准确;利用摆位误差计算得到的CTV-PTV外扩边界,可能对增加疗效和减小正常器官副反应有重要意义.%Objective:To discuss methods of dose verification and setup error for patients with nasopharyngeal carcinoma (NPC) treatment by image guided intensity modulated radiotherapy (IG-IMRT). Methods: Thirty-two patients with NPC were treated by IG-IMRT to develop X-ray kilovolt cone beam computed tomography (CBCT). The acquired CBCT was registered to the planning CT for online analysis. The patient setup errors were defined as the offset between CBCT and planning CT in the Left-Right(LR), Superior-Inferior(SI) and Anterior-Posterior(AP) directions, and the different treatment times of pre-treat-ment, post-correction and post-treatment All these CBCTs were 426、116、36 fractions respectively. We developed Gamma value and absolute dose value (＜4%) to evaluate the accuracy of MRT plans based on 2D ionization chambers array. Results: 'All 426 sets of CBCT image were analyzed for 32 patients. Under the condition of non-correction, the setup isocenter errors were (0.44±2.03) mm、 (0.51±2.75) mm、(-0.37±2.14) mm in Left-Right, Superior-Inferior and Anterior-Posterior directions respectively in the pre-treatment .After correction and post-treatment, the setup errors were (0.07±0.59) mm,(0.07±0.80) mm、 (-0.02±0.75) mm; (0.19±0.59) mm、(0.15±0.73) mm、(-0.08±0.72) mm in the three directions .And in the target regions dose verification ,the Gamma value of each beam of me plan was 88.2% ～99.2%,and the value was 90.2% ～99.7% in the each plan.The absolute dose value was chosen from five points among the high dose region 、low dose region、isocenter、high gratitude dose religion and dose flatness region. All the dose deviation was in the -3.9% ～ 4.2%.Conclusions: CBCT-based online correction and individual dose verification will ensure the accuracy of IG-IMRT for NPC and reduce irradiated margins. It will reduce dose of the risk organs, so which will reduce normal tissues treatment-related toxicity, and increase tumors control rate.