Han Eun Young, Kim Gwe-Ya, Rebueno Neal, Yeboa Debra N, Briere Tina M
Department of Radiation Physics, Unit 94, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, CA 92093, USA.
Med Dosim. 2019;44(4):e44-e50. doi: 10.1016/j.meddos.2018.12.006. Epub 2019 Jan 14.
For external beam stereotactic radiosurgery of multiple brain metastatic lesions, it is difficult to select optimal treatment isocenters because the orientation and volume of each planning target volume (PTV) and its proximity to critical structures are unique for each patient. The RayStation treatment planning system offers Python-based scripting to optimize the placement of the treatment isocenter by comparing scenario-based plans. This can improve the plan quality by reducing the dose to the normal brain and increasing planning efficiency. The purpose of the current study was to compare the isocenter-optimized plans generated by RayStation with clinical plans created by the Pinnacle treatment planning system and to validate the RayStation treatment planning and delivery with end-to-end testing. Ten patient plans were automatically regenerated using the script in RayStation. For each patient, 4 plans with 4 different types of isocenters were generated: (1) 2 separate isocenters at the PTV centroids, (2) a single isocenter at the mid-point of 2 centroids, (3) a single isocenter at PTV1, and (4) a single isocenter at PTV2. The best plans were compared with paired Pinnacle plans using plan quality parameters, including normal brain volume excluding PTVs receiving 4 Gy (V), normal brain volume excluding PTVs receiving 12 Gy (V), maximum dose to the brainstem, homogeneity index, conformity indices, gradient index of each PTV, and monitor units per fraction. All plans were verified with a cylindrical quality assurance phantom, and end-to-end testing was performed with an anthropomorphic head phantom with a radiochromic film. The script was executed within 5-6 minutes to generate 4 scenario-based automatic plans. The homogeneity index and conformity indices showed small but statistically significant improvement with the RayStation plans. The gradient index (3.9 ± 0.9 for Pinnacle and 3.5 ± 0.6 for RayStation, p = 0.04) was also more favorable in the RayStation plans. V was significantly reduced by 13% and V was reduced by 5%. The total monitor units per fraction was significantly reduced by 20% for the RayStation plans. Plan optimization time using RayStation was reduced by 64%. The measured doses at each PTV centroid agreed within 3%, and all RayStation plans passed quality assurance verification tests. Scenario-based automatic plan generation using Python scripting helps identify an optimal treatment isocenter to reduce the dose to the normal brain and improve planning efficiency. RayStation plans provided better plan quality, especially lower doses to the normal brain, than Pinnacle plans. Thus, RayStation is a suitable planning modality for hypofractionated stereotactic radiosurgery for multiple brain metastases.
对于多脑转移瘤的外照射立体定向放射外科治疗，由于每个计划靶区（PTV）的方向、体积及其与关键结构的接近程度在每个患者中都是独特的，因此很难选择最佳治疗等中心。RayStation治疗计划系统提供基于Python的脚本，通过比较基于场景的计划来优化治疗等中心的放置。这可以通过减少对正常脑组织的剂量和提高计划效率来改善计划质量。本研究的目的是比较RayStation生成的等中心优化计划与Pinnacle治疗计划系统创建的临床计划，并通过端到端测试验证RayStation治疗计划和实施。使用RayStation中的脚本自动重新生成了10个患者计划。对于每个患者，生成了4个具有4种不同类型等中心的计划：（1）在PTV质心处的2个单独等中心，（2）在2个质心中点处的单个等中心，（3）在PTV1处的单个等中心，以及（4）在PTV2处的单个等中心。使用计划质量参数将最佳计划与配对的Pinnacle计划进行比较，这些参数包括排除接受4 Gy的PTV后的正常脑体积（V）、排除接受12 Gy的PTV后的正常脑体积（V）、脑干的最大剂量、均匀性指数、适形指数、每个PTV的梯度指数以及每分次的监测单位。所有计划均使用圆柱形质量保证体模进行验证，并使用带有放射变色胶片的拟人化头部体模进行端到端测试。该脚本在5 - 6分钟内执行完毕，以生成4个基于场景的自动计划。均匀性指数和适形指数在RayStation计划中显示出虽小但具有统计学意义的改善。梯度指数（Pinnacle为3.9±0.9，RayStation为3.5±0.6，p = 0.04）在RayStation计划中也更有利。V显著降低了13%，V降低了5%。RayStation计划的每分次总监测单位显著减少了20%。使用RayStation的计划优化时间减少了64%。在每个PTV质心处测量的剂量在3%以内一致，并且所有RayStation计划均通过了质量保证验证测试。使用Python脚本基于场景的自动计划生成有助于确定最佳治疗等中心，以减少对正常脑的剂量并提高计划效率。与Pinnacle计划相比，RayStation计划提供了更好的计划质量，尤其是对正常脑的剂量更低。因此，RayStation是用于多脑转移瘤的低分割立体定向放射外科治疗的合适计划方式。
