Elcim Yelda, Dirican Bahar, Yavas Omer
Department of Radiation Oncology, Gulhane Training and Research Hospital, Ankara, Turkey.
Department of Engineering Physics, Ankara University, Ankara, Turkey.
J Appl Clin Med Phys. 2018 Sep;19(5):616-624. doi: 10.1002/acm2.12426. Epub 2018 Aug 5.
In this study, lung radiotherapy target volumes as well as critical organs such as the lungs, spinal cord, esophagus, and heart doses calculated using pencil beam (PB) and Monte Carlo (MC) algorithm-based treatment planning systems (TPSs) were compared. The main aim was the evaluation of calculated dose differences between the PB and MC algorithms in a highly heterogeneous medium.
A total of 6 MV photon energy conformal treatment plans were created for a RANDO lung phantom using one PB algorithm-based Precise Plan Release 2.16 TPS and one MC algorithm-based Monaco TPS. Thermoluminescence dosimeters (TLDs) were placed into appropriate slices within the RANDO phantom and then irradiated with an Elekta-Synergy Linear Accelerator for dose verification. Doses were calculated for the V5, V10, V20, and mean lung doses (MLDs) in bilateral lungs and D50, D98, D2, and mean doses in the target volume (planning target volume, PTV).
The minimum, maximum, and mean doses of the target volumes and critical organs in two treatment plans were compared using dose volume histograms (DVHs). The mean dose difference between the PB and MC algorithms for the PTV was 0.3%, whereas the differences in V5, V10, V20, and MLD were 12.5%, 15.8%, 14.4%, and 9.1%, respectively. The differences in PTV coverage between the two algorithms were 0.9%, 2.7% and 0.7% for D50, D98 and D2, respectively.
A comparison of the dose data acquired in this study reveals that the MC algorithm calculations are closer to the 60 Gy prescribed dose for PTV, while the difference between the PB and MC algorithms was found to be non-significant. Because of the major difference arising from the dose calculation techniques by TPS that was observed in the MLD with significant medium heterogeneity, we recommend the use of the MC algorithm in such heterogeneous sites.
在本研究中，比较了使用笔形束（PB）和基于蒙特卡罗（MC）算法的治疗计划系统（TPS）计算的肺放疗靶区体积以及肺、脊髓、食管和心脏等关键器官的剂量。主要目的是评估在高度异质介质中PB和MC算法之间计算剂量的差异。
使用一个基于PB算法的Precise Plan Release 2.16 TPS和一个基于MC算法的Monaco TPS，为RANDO肺模体创建了总共6 MV光子能量的适形治疗计划。将热释光剂量计（TLD）放置在RANDO模体内的适当切片中，然后用Elekta-Synergy直线加速器进行照射以进行剂量验证。计算双侧肺的V5、V10、V20和平均肺剂量（MLD）以及靶区体积（计划靶区，PTV）中的D50、D98、D2和平均剂量。
使用剂量体积直方图（DVH）比较了两个治疗计划中靶区体积和关键器官的最小、最大和平均剂量。PTV的PB和MC算法之间的平均剂量差异为0.3%，而V5、V10、V20和MLD的差异分别为12.5%、15.8%、14.4%和9.1%。两种算法在PTV覆盖方面的差异，D50、D98和D2分别为0.9%、2.7%和0.7%。
本研究中获取的剂量数据比较表明，MC算法计算结果更接近PTV规定的60 Gy剂量，而PB和MC算法之间的差异不显著。由于在具有显著介质异质性的MLD中观察到TPS剂量计算技术存在重大差异，我们建议在这种异质部位使用MC算法。
