Adapt-On-Demand: A Novel Strategy for Personalized Adaptive Radiotherapy for Locally Advance Lung Cancer.

PURPOSE: Real time adaptation of thoracic radiation plans is compelling because offline adaptive experiences show that tumor volumes and lung anatomy can change during therapy. We present and analyze a novel adaptive-on-demand (AOD) workflow combining online adaptive radiotherapy (ART) on the ETHOS system with image-guided radiotherapy (IGRT) delivery on a Halcyon unit for conventional fractionated radiotherapy of locally advanced lung cancer (LALC).

METHOD: We analyzed 26 LALC patients treated with the AOD workflow, adapting weekly. We timed segments of the workflow to evaluate efficiency in a real world clinic. Target coverage and OAR doses were compared between adapted plans (ADP) and scheduled plans without adaptation (SCH). Planning robustness was evaluated by the frequency of preplanning goals being achieved in ADP plans, stratified by tumor volume change.

RESULTS: The AOD workflow was achievable within 30 min for most radiation fractions. Over the course of therapy we observed an average 26.6% ± 23.3% reduction in ITV volumes. Despite these changes, with online adaptive radiation therapy (o-ART), ITV and PTV coverage (V100%) was 99.2% and 93.9% for all members of the cohort. This represented a 2.9% and 6.8% improvement over non-adapted plans (p<0.05). For tumors that grew > 10%, V100% was 93.1% for o-ART, while it was 76.4% for non-adaptive plans, representing a median 17.2% improvement in the PTV coverage (p < 0.05). In these plans, critical OAR constraints were met 94.1% of the time, whereas in non-adapted plans it was 81.9%. This represented reductions of 1.32 Gy, 1.34 Gy, or 1.75 Gy in heart, esophagus, and lung, respectively. The effect was larger when tumors had shrunk more than 10%. Regardless of tumor volume alterations, the PTV/ITV coverage was achieved for all adaptive plans. Exceptional cases, where dose constraints were not met, were due to large initial tumor volumes or tumor growth.

CONCLUSION: The AOD workflow is efficient and robust in responding to anatomical changes in LALC patients, providing dosimetric advantages over standard therapy. Weekly adaptation was adequate to keep pace with changes. This approach is a feasible alternative to conventional offline replanning workflows for managing anatomy changes in LALC radiotherapy.