Estimation of accumulated dose to organs at risk in head and neck cancer patients treated with scheduled replanning and dose painting in the ARTFORCE trial

Background and purpose: This study investigated whether scheduled adaptive radiotherapy (ART) improved delivered dose to organs at risk (OAR) in patients with locally advanced head and neck cancer treated with dose painting (DP). Materials and methods: Delivered doses were estimated for 81 patients who were prospectively treated with DP + ART using deformable image registration between CBCT and the planning CT’s. Three simulations were conducted, evaluating (1) a scenario without replanning (Sim_noART), (2) a scenario with ART at fraction 12 (Sim_ART), and (3) the clinical practice with ad hoc replanning (Sim_delivered). It was further evaluated whether selecting patients for ART using accumulated dose in the first 10 fractions (Df10) to the parotid glands and larynx would improve ART efficacy. Results: In Sim_noART, 41% of patients had delivered dose deviations ≥ 3 Gy compared to the planned dose in any OAR, primarily in the parotid glands and larynx. No significant differences were seen between Sim_noART, Sim_ART and Sim_delivered (P ≥ 0.10). Df10 predicted relevant changes upon completing treatment with AUC ≥ 0.95. By selecting patients for ART using Df10, delivered dose significantly improved for the larynx (P ≤ 0.01). Conclusions: Although relevant dose differences between planned and delivered doses were seen in almost half of the patients without ART, minimal improvements in delivered doses were seen introducing ART. Nonetheless, Df10 was prognostic for relevant changes upon completing treatment and selecting patients for ART significantly improved larynx dose. Incorporating accumulated dose into patient selection for ART could help avoid unforeseen increases in delivered dose.