3597 - Dosimetric Evaluation of Organs-at-Risk and Quality of Life Assessment between Standard of Care and Dose De-Escalated Radiation in HPV Positive Oropharyngeal Cancer

G. B. Biedermann, A. Abdalla, and J. Overschmidt; University of Missouri, Columbia, MO

Purpose/Objective(s): We are currently conducting a de-escalation trial in HPV-related oropharyngeal SCC (ENID) and have completed an interim analysis. Previously, we enrolled patients on the PEG study which assessed factors that predict PEG tube placement in patients receiving RT for head and neck cancer. The primary objective of this analysis is to compare dosimetry to organs-at-risk (OARs) between patients on the ENID trial to HPV positive subgroup on the PEG trial, as well as to report and compare quality of life measures between the two different groups of study participants undergoing radiation treatment to the oropharynx. We expected that the de-escalation group will have a reduced dose to OARs and thus will have better quality of life outcomes. Materials/

Methods: The ENID group was treated with 40 Gy in 20 fractions to the known disease and elective lymph nodes and a subsequent boost was delivered to the PET-defined gross disease for an additional 30 Gy in 15 fractions. The PEG group was treated with the standard of care treatment: 70 Gy in 35 fractions to both PET-defined gross disease and 56 Gy in 35 fractions to the elective lymph nodes. In both studies, patients completed questionnaires including the Edmonton Symptom Assessment System (ESAS) and the EORTC QLQ-H&N35. For this analysis, we assessed 1-month and 3-month post-RT outcomes, and we compared dosimetry to the multiple OARs. We completed two-sample t-tests for the quality-of-life measures and dosimetry values.
Results: The ENID group included 18 patients and the PEG sub-group included 16 patients. The results of the QOL measures between the two groups were not statistically significant, but we did report improved outcomes at 3 months in the ENID group. In addition, The OARs between the two groups were statistically significant for contralateral submandibular gland, parotid gland, oral cavity and thyroid, indicating a statistically significant reduction in dose in the de-escalation group.
Conclusion: This study reports encouraging outcomes regarding reducing RT dose to OARs, as expected, when utilizing de-escalation to the elective lymph nodes. We previously reported excellent local control. This study did show a difference in QOL outcomes, but it was not significant, and it is important to note this is a small sample size. Based on the reduction of dose to OARs, we expect to see more improvement at the later time points as well.