Syam Kumar S A, Vivekanandan Nagarajan, Sriram Padmanaban
Medical Physics Department, Cancer Institute (WIA), Adyar, Chennai, TamilNadu, India.
Rep Pract Oncol Radiother. 2012 Mar 3;17(3):168-75. doi: 10.1016/j.rpor.2012.01.009. eCollection 2012.
To evaluate the performance of volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.
RapidArc is a novel technique that has recently been made available for clinical use. Planning study was done for volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.
Ten patients with advanced tumors of the nasopharynx, oropharynx, and hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning was done by means of simultaneously integrated boost technique. A total dose of 70 Gy was delivered to the boost volume (PTV boost) and 57.7 Gy to the elective PTV (PTV elective) in 35 equal treatment fractions. PTV boost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes, whereas the PTV elective consisted of elective nodal regions. Planning was done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam was equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360° gantry rotation and double arc consists of 2 co-planar arcs of 360° in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45° to cover the entire tumor, which reduced the tongue and groove effect during gantry rotation. All plans were generated with 6 MV X-rays for CLINAC 2100 Linear Accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm.
Double arc plans show superior dose homogeneity in PTV compared to a single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in the double arc technique by 4.5% when compared to the IMRT 9 field and single arc techniques. For healthy tissue, no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V 15 Gy (5.81% for single arc and 4.69% for double arc) and V 20 Gy (7.55% for single arc and 5.89% for double arc) dose levels when compared to the 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200 cGy per fraction was 474 ± 80 MU and 447 ± 45 MU for double arc and single arc as against 948 ± 162 MU for the 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc shows a reduction in the parotid mean dose when compared with single arc and IMRT plans.
RapidArc using double arc provided a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The main disadvantage with IMRT observed was higher monitor units and longer treatment time.
评估容积弧形调强放疗（RapidArc）与传统调强放疗（IMRT）对头颈部癌的治疗效果。
RapidArc是一项最近可供临床使用的新技术。对头颈部癌进行了容积弧形调强放疗（RapidArc）与传统调强放疗（IMRT）的计划研究。
选择10例患有晚期鼻咽癌、口咽癌和下咽癌的患者进行计划对比研究。针对两种不同剂量水平勾画计划靶区（PTV），并采用同步整合加量技术进行计划制定。在35个等份治疗分次中，向加量靶区（PTV加量）给予70 Gy的总剂量，向选择性PTV（PTV选择性）给予57.7 Gy的总剂量。PTV加量包括大体肿瘤体积和包含可见宏观肿瘤或活检证实为阳性淋巴结的淋巴结，而PTV选择性包括选择性淋巴结区域。使用9野进行IMRT计划制定，使用单弧、双弧进行RapidArc计划制定。IMRT计划的射野均匀分布。单弧RapidArc计划利用360°的全机架旋转，双弧由顺时针和逆时针方向的2个共面360°弧组成。准直器从35°旋转到45°以覆盖整个肿瘤，这减少了机架旋转期间的舌槽效应。所有计划均使用用于CLINAC 2100直线加速器的6 MV X射线生成。在Eclipse治疗计划系统（8.6版）中使用AAA算法进行计算。
与单弧和IMRT 9野技术相比，双弧计划在PTV中显示出更好的剂量均匀性。所有技术的靶区覆盖情况几乎相似。与IMRT 9野和单弧技术相比，双弧技术在脊髓最大剂量方面的保护效果更好，降低了4.5%。对于健康组织，各计划在平均剂量和积分剂量方面未观察到显著变化。但与9野IMRT技术相比，RapidArc计划在V 15 Gy（单弧为5.81%，双弧为4.69%）和V 20 Gy（单弧为7.55%，双弧为5.89%）剂量水平下照射的健康组织体积有所减少。对于脑干，所有技术的最大剂量相似。双弧和单弧每分次给予200 cGy剂量所需的平均监测单位（±标准差）分别为447 ± 45 MU和474 ± 80 MU，而9野IMRT计划为948 ± 162 MU。双弧计划使下颌骨的最大剂量显著降低了6.05%。与单弧和IMRT计划相比，双弧显示腮腺平均剂量降低。
与IMRT相比，使用双弧的RapidArc在不影响靶区覆盖的情况下，显著减少了危及器官和健康组织的受照剂量。观察到的IMRT的主要缺点是监测单位较高和治疗时间较长。
