Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
Med Phys. 2011 Sep;38(9):5104-18. doi: 10.1118/1.3622612.
A novel rotational IMRT (rIMRT) technique using burst delivery (continuous gantry rotation with beam off during MLC repositioning) is investigated. The authors evaluate the plan quality and delivery efficiency and accuracy of this dynamic technique with a conventional flat 6 MV photon beam.
Burst-delivery rIMRT was implemented in a planning system and delivered with a 160-MLC linac. Ten rIMRT plans were generated for five anonymized patient cases encompassing head and neck, brain, prostate, and prone breast. All plans were analyzed retrospectively and not used for treatment. Among the varied plan parameters were the number of optimization points, number of arcs, gantry speed, and gantry angle range (alpha) over which the beam is turned on at each optimization point. Combined rotational/step-and-shoot rIMRT plans were also created by superimposing multiple-segment static fields at several optimization points. The rIMRT trial plans were compared with each other and with plans generated using helical tomotherapy and VMAT. Burst-mode rotational IMRT plans were delivered and verified using a diode array, ionization chambers, thermoluminescent dosimeters, and film.
Burst-mode rIMRT can achieve plan quality comparable to helical tomotherapy, while the former may lead to slightly better OAR sparing for certain cases and the latter generally achieves slightly lower hot spots. Few instances were found in which increasing the number of optimization points above 36, or superimposing step-and-shoot IMRT segments, led to statistically significant improvements in OAR sparing. Using an additional rIMRT partial arc yielded substantial OAR dose improvements for the brain case. Measured doses from the rIMRT plan delivery were within 4% of the plan calculation in low dose gradient regions. Delivery time range was 228-375 s for single-arc rIMRT 200-cGy prescription with a 300 MU/min dose rate, comparable to tomotherapy and VMAT.
Rotational IMRT with burst delivery, whether combined with static fields or not, yields clinically acceptable and deliverable treatment plans.
研究了一种新型的旋转调强放射治疗（rIMRT）技术，该技术采用突发传输（在叶片重新定位期间连续旋转机架，同时关闭光束）。作者使用常规的平板 6MV 光子束评估了这种动态技术的计划质量和传输效率及精度。
突发传输 rIMRT 在计划系统中实现，并使用 160 叶片直线加速器进行传输。为涵盖头颈部、脑部、前列腺和俯卧位乳房的 5 个匿名患者病例生成了 10 个 rIMRT 计划。所有计划均进行回顾性分析，而不用于治疗。在各种计划参数中，有优化点的数量、弧的数量、机架速度以及在每个优化点处打开光束的机架角度范围（alpha）。通过在几个优化点处叠加多个分段静态场，也创建了旋转/分步放射治疗的综合 rIMRT 计划。将 rIMRT 试验计划相互比较，并与螺旋断层放疗和容积旋转调强放射治疗（VMAT）生成的计划进行比较。使用二极管阵列、电离室、热释光剂量计和胶片对突发模式旋转 IMRT 计划进行传输和验证。
突发模式 rIMRT 可以达到与螺旋断层放疗相当的计划质量，而前者可能导致某些情况下 OAR 保护略有改善，后者通常会导致热点略低。在增加优化点数量超过 36 个或叠加分步放射治疗段的情况下，发现很少有实例导致 OAR 保护的统计学显著改善。对于脑部病例，使用额外的 rIMRT 部分弧可以显著改善 OAR 剂量。在低剂量梯度区域，rIMRT 计划传输的测量剂量与计划计算值相差在 4%以内。对于 300MU/min 剂量率的单弧 200cGy 处方，rIMRT 的传输时间范围为 228-375s，与螺旋断层放疗和 VMAT 相当。
无论是否与静态场结合，突发传输的旋转调强放射治疗都可以产生临床可接受且可传输的治疗计划。
