Dual Method Quantitative QA for Head and Neck Offline Adaptive Radiotherapy Utilizing Transmission Portal Dosimetry and Contour-Based Assessment
Abstract
Purpose
Adaptive radiotherapy (ART) for head and neck (HN) cancer helps maintain target coverage and spare organs-at-risk (OARs) despite anatomical changes like weight loss. For clinics without online ART, early identification of patients needing replanning is essential. This work evaluates a tiered QA strategy where rapid portal dosimetry monitoring triggers contour‑adaptive plan assessment to detect clinically-relevant deviations.
Methods
A sequential imaging analysis framework was developed to support ART. Daily portal transmission-dosimetry from Halcyon machines was analyzed using gamma criteria: ≥95% of points with γ95% with average gamma 0.19±0.08. Patients needing replanning showed progressive deterioration, with 45.6% of fractions failing criteria and average gamma rising from 0.18 to 0.54 prior to starting a new plan. For the same patient, contour‑adaptive QA demonstrated reduced CTV coverage (from >98% to 91% and 95% for the 70Gy and 58Gy targets) and increased dose above the clinical goals to the oral cavity, parotids, and submandibular glands.
Conclusion
Portal dosimetry offers rapid, automated screening that can trigger contour‑adaptive QA, enabling efficient detection of anatomical change and supporting earlier replanning with minimal workflow burden.