Dosimetric Analysis of Online Adaptive Radiation Therapy in the Adjuvant Setting for Head and Neck Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Online adaptive radiotherapy (OnART) system designed to deliver re-optimized plans in real time using on-board cone beam CT and artificial intelligence has enabled frequent adaptation. Given the paucity of data on the role of adaptive radiotherapy (RT) and its frequency in the treatment of post-operative patients with head and neck squamous cell carcinoma (HNSCC), a dosimetric study was performed to assess the potential benefits of a single vs weekly OnART in this setting. <h3>Materials/Methods</h3> Twelve patients receiving conventionally fractionated RT (CFRT) over 6 weeks and 12 patients receiving hypofractionated RT (HFRT) over 3 weeks on a clinical trial between 2020 and 2021 were analyzed. The OnART plan was generated to meet the same quality as the original clinical plan and the OnART emulator was used to virtually conduct adaptive RT based on the patient's cone beam CT. The PTV coverage, dose heterogeneity, and cumulative dose to the organs-at-risk of a single mid-treatment OnART (at week 4 for CFRT and week 2 for HFRT) and weekly OnART were compared to the non-adapted plan. <h3>Results</h3> In total, 13, 8, and 3 patients had oral cavity, oropharynx, and larynx primaries, respectively, with 11 of the 24 patients receiving ipsilateral RT only. The average absolute and % weight loss during treatment were 5.7 lb and 3.1%, respectively. In the CFRT cohort, weekly OnART led to a significant improvement in high risk PTV (PTVHR) and standard risk PTV (PTVSR) V100 coverage (9.9% and 3.4% absolute) as well as hot spot (-1.3 Gy), max cord dose (-3.4 Gy), and mean oral cavity dose (-1.3 Gy), while the mean contralateral parotid dose increased modestly (0.76 Gy) (Table). When adapted once, only PTVHR coverage was improved (3.3%). For the HFRT cohort, weekly OnART resulted in a significant improvement in PTVHR/PTVSR coverage (3.7%/2.0%), hot spot (-0.82 Gy), and max cord dose (-2.5 Gy) (Table). When adapted once, mean oral cavity dose decreased (-1.4 Gy) and mean contralateral parotid dose increased (1.1 Gy). <h3>Conclusion</h3> There was a limited benefit of one-time OnART, but weekly adaptations improved the dosimetry, predominantly in PTV coverage and dose heterogeneity for patients receiving adjuvant RT for HNSCC. A prospective study is ongoing to determine the potential benefit in clinical and patient-reported outcomes of OnART in this setting.