Clinical Experience With an Offline Adaptive Radiation Therapy Head and Neck Program: Dosimetric Benefits and Opportunities for Patient Selection

Abstract

PurposeTo develop a LINAC-based adaptive radiotherapy (ART) workflow for head and neck that is informed by automated image tracking to identify major anatomic changes warranting adaptation. In this study we report our initial clinical experience with the program and an investigation into potential trigger signals for ART. Methods and MaterialsOffline ART was systematically performed on patients receiving radiotherapy for head and neck cancer on C-arm LINACs. Adaptations were performed at a single timepoint during treatment with resimulation approximately 3 weeks into treatment. Throughout treatment, all patients were tracked using an automated image tracking system called the IN_HOUSE_SOFTWARE*. IN_HOUSE_SOFTWARE measures volumetric changes in gross tumor volumes (GTV) and selected normal tissues via cone-beam computed tomography (CBCT) scans and deformable registration. The benefit of ART was determined by comparing adaptive plan dosimetry and normal tissue complication probabilities (NTCP) against the initial plans recalculated on resimulation CT scans. Dosimetric differences were then correlated with IN_HOUSE_SOFTWARE-measured volume changes to identify patient-specific triggers for ART. Candidate trigger variables were evaluated using receiver operator characteristic (ROC) analysis. ResultsN=46 patients received ART in this study. Amongst these patients, we observed a significant decrease in dose to the submandibular glands (mean ± standard deviation: -219.2±291.2cGy, p-value<10−5), parotids (-68.2±197.7cGy, p-value=0.001) and oral cavity (-238.7±206.7cGy, p-value<10−5) with the adaptive plan. NTCPs for xerostomia computed from mean parotid doses also decreased significantly with the adaptive plans (p-value=0.008). We also observed systematic intra-treatment volume reductions (ΔV) for GTVs and normal tissues. Candidate triggers were identified which did predict significant improvement with ART including parotid ΔV=7%, neck ΔV=2%, and nodal GTV ΔV=29%. ConclusionsSystematic offline head and neck ART was successfully deployed on conventional LINACs and reduced doses to critical salivary structures and oral cavity. Automated CBCT tracking provided information regarding anatomic changes that may aid patient-specific triggering for ART. (*Anonymized for review)