Treatment plan quality during online adaptive re-planning
Janita E. van Timmeren, M. Chamberlain, J. Krayenbuehl, L. Wilke, Stefanie Ehrbar, Marta Bogowicz, Callum Hartley, M. Zamburlini, Nicolaus Andratschke, Helena Garcia Schüler, Matea Pavic, Panagiotis Balermpas, Chaehee Ryu, Matthias Gückenberger, Stephanie Tanadini‐Lang
Abstract
Abstract Background Online adaptive radiotherapy is intended to prevent plan degradation caused by inter-fractional tumor volume and shape changes, but time limitations make online re-planning challenging. The aim of this study was to compare the quality of online-adapted plans to their respective reference treatment plans. Methods Fifty-two patients treated on a ViewRay MRIdian Linac were included in this retrospective study. In total 238 online-adapted plans were analyzed, which were optimized with either changing of the segment weights ( n = 85) or full re-optimization ( n = 153). Five different treatment sites were evaluated: prostate, abdomen, liver, lung and pelvis. Dosimetric parameters of gross tumor volume (GTV), planning target volume (PTV), 2 cm ring around the PTV and organs at risk (OARs) were considered. The Wilcoxon signed-rank test was used to assess differences between online-adapted and reference treatment plans, p < 0.05 was considered significant. Results The average duration of the online adaptation, consisting of contour editing, plan optimization and quality assurance (QA), was 24 ± 6 min. The GTV was slightly larger (average ± SD: 1.9% ± 9.0%) in the adapted plans than in the reference plans ( p < 0.001). GTV-D 95% exhibited no significant changes when considering all plans, but GTV-D 2% increased by 0.40% ± 1.5% on average ( p < 0.001). There was a very small yet significant decrease in GTV-coverage for the abdomen plans. The ring D mean increased on average by 1.0% ± 3.6% considering all plans ( p < 0.001). There was a significant reduction of the dose to the rectum of 4.7% ± 16% on average ( p < 0.001) for prostate plans. Conclusions Dosimetric quality of online-adapted plans was comparable to reference treatment plans and OAR dose was either comparable or decreased, depending on treatment site. However, dose spillage was slightly increased.