Bazalova-Carter Magdalena, Qu Bradley, Palma Bianey, Hårdemark Björn, Hynning Elin, Jensen Christopher, Maxim Peter G, Loo Billy W
Department of Radiation Oncology, Stanford University, Stanford, California 94305.
RaySearch Laboratories AB, Stockholm SE-103 65, Sweden.
Med Phys. 2015 May;42(5):2615-25. doi: 10.1118/1.4918923.
The aim of this work was to develop a treatment planning workflow for rapid radiotherapy delivered with very high-energy electron (VHEE) scanning pencil beams of 60-120 MeV and to study VHEE plans as a function of VHEE treatment parameters. Additionally, VHEE plans were compared to clinical state-of-the-art volumetric modulated arc therapy (VMAT) photon plans for three cases.
VHEE radiotherapy treatment planning was performed by linking EGSnrc Monte Carlo (MC) dose calculations with inverse treatment planning in a research version of RayStation. In order to study the effect of VHEE treatment parameters on VHEE dose distributions, a matlab graphical user interface (GUI) for calculation of VHEE MC pencil beam doses was developed. Through the GUI, pediatric case MC simulations were run for a number of beam energies (60, 80, 100, and 120 MeV), number of beams (13, 17, and 36), pencil beam spot (0.1, 1.0, and 3.0 mm) and grid (2.0, 2.5, and 3.5 mm) sizes, and source-to-axis distance, SAD (40 and 50 cm). VHEE plans for the pediatric case calculated with the different treatment parameters were optimized and compared. Furthermore, 100 MeV VHEE plans for the pediatric case, a lung, and a prostate case were calculated and compared to the clinically delivered VMAT plans. All plans were normalized such that the 100% isodose line covered 95% of the target volume.
VHEE beam energy had the largest effect on the quality of dose distributions of the pediatric case. For the same target dose, the mean doses to organs at risk (OARs) decreased by 5%-16% when planned with 100 MeV compared to 60 MeV, but there was no further improvement in the 120 MeV plan. VHEE plans calculated with 36 beams outperformed plans calculated with 13 and 17 beams, but to a more modest degree (<8%). While pencil beam spacing and SAD had a small effect on VHEE dose distributions, 0.1-3 mm pencil beam sizes resulted in identical dose distributions. For the 100 MeV VHEE pediatric plan, OAR doses were up to 70% lower and the integral dose was 33% lower for VHEE compared to 6 MV VMAT. Additionally, VHEE conformity indices (CI100 = 1.09 and CI50 = 4.07) were better than VMAT conformity indices (CI100 = 1.30 and CI50 = 6.81). The 100 MeV VHEE lung plan resulted in mean dose decrease to all OARs by up to 27% for the same target coverage compared to the clinical 6 MV flattening filter-free (FFF) VMAT plan. The 100 MeV prostate plan resulted in 3% mean dose increase to the penile bulb and the urethra, but all other OAR mean doses were lower compared to the 15 MV VMAT plan. The lung case CI100 and CI50 conformity indices were 3% and 8% lower, respectively, in the VHEE plan compared to the VMAT plan. The prostate case CI100 and CI50 conformity indices were 1% higher and 8% lower, respectively, in the VHEE plan compared to the VMAT plan.
The authors have developed a treatment planning workflow for MC dose calculation of pencil beams and optimization for treatment planning of VHEE radiotherapy. The authors have demonstrated that VHEE plans resulted in similar or superior dose distributions for pediatric, lung, and prostate cases compared to clinical VMAT plans.
本研究旨在开发一种用于60 - 120 MeV超高能电子（VHEE）扫描笔形束快速放疗的治疗计划工作流程，并研究VHEE计划作为VHEE治疗参数的函数关系。此外，针对三个病例，将VHEE计划与临床先进的容积调强弧形放疗（VMAT）光子计划进行了比较。
通过将EGSnrc蒙特卡罗（MC）剂量计算与RayStation研究版中的逆向治疗计划相链接，进行VHEE放射治疗治疗计划。为了研究VHEE治疗参数对VHEE剂量分布的影响，开发了一个用于计算VHEE MC笔形束剂量的Matlab图形用户界面（GUI）。通过该GUI，针对多个束能量（60、80、100和120 MeV）、束数（13、17和36）、笔形束光斑（0.1、1.0和3.0 mm）和网格（2.0、2.5和3.5 mm）尺寸以及源轴距，SAD（40和50 cm），对儿科病例进行了MC模拟。对使用不同治疗参数计算的儿科病例的VHEE计划进行了优化和比较。此外，计算了儿科病例、肺部病例和前列腺病例的100 MeV VHEE计划，并与临床实施的VMAT计划进行了比较。所有计划均进行归一化处理，以使100%等剂量线覆盖95%的靶体积。
VHEE束能量对儿科病例剂量分布质量的影响最大。对于相同的靶剂量，与60 MeV相比，使用100 MeV进行计划时，危及器官（OARs）的平均剂量降低了5% - 16%，但120 MeV计划没有进一步改善。用36束计算的VHEE计划优于用13束和17束计算的计划，但改善程度较小（<8%）。虽然笔形束间距和SAD对VHEE剂量分布影响较小，但0.1 - 3 mm的笔形束尺寸导致相同的剂量分布。对于100 MeV VHEE儿科计划，与6 MV VMAT相比，VHEE的OAR剂量降低了高达70%，积分剂量降低了33%。此外，VHEE的适形指数（CI100 = 1.09和CI50 = 4.07）优于VMAT的适形指数（CI100 = 1.30和CI50 = 6.81）。与临床6 MV无 flattening filter（FFF）VMAT计划相比，100 MeV VHEE肺部计划在相同靶区覆盖情况下，所有OAR的平均剂量降低了高达27%。100 MeV前列腺计划导致阴茎球部和尿道的平均剂量增加了3%，但与15 MV VMAT计划相比，所有其他OAR的平均剂量更低。在VHEE计划中，肺部病例的CI100和CI50适形指数分别比VMAT计划低3%和8%。前列腺病例的VHEE计划中，CI100和CI50适形指数分别比VMAT计划高1%和低8%。
作者开发了一种用于笔形束MC剂量计算和VHEE放射治疗治疗计划优化的治疗计划工作流程。作者证明，与临床VMAT计划相比，VHEE计划在儿科、肺部和前列腺病例中产生了相似或更好的剂量分布。
