Fifty-sixth annual meeting of the American association of physicists in medicine
SU-E-T-612: Reducing Toxicity in HPV+ Head and Neck Patients: Dose De- Escalation Or PTV Elimination?
Studies have shown that patients diagnosed with HPV positive head and neck cancer have a higher probability of local control and 5 year survival. For these patients, reducing treatment related toxicities have become a clinical focus. Two primary strategies exist to reduce the risk of complications: dose de-escalation and/or PTV reduction. The goal of this planning study is to evaluate which strategy would have the greatest potential for reducing toxicity.
Patients treated with volumetric modulated arc therapy (VMAT) were re-planned based on 2 scenarios: A) eliminating the PTV and keeping the same planned dose to the CTV (assuming that daily dose assessment would be performed and plan adaptation when necessary) and B) dose de-escalation to 54 Gy (following the ECOG Phase II trial (E1308) schema). The target D99 and D95 was maintained for all planning scenarios as per the dose level. The mean dose to the superior constrictor (SC), left and right parotid glands (LPG, RPG), and left and right submandibular glands (LSG, RSG) were evaluated for each planning scenario.
Dose de-escalation to 54 Gy achieved greater sparing of all structures compared to eliminating the PTV while maintaining the planned dose. The average sparing with the dose de-escalation was 10, 5.7, 5.2, 8.6, and 8.1 Gy for the SC, LPG, RPG, LSG, and RSG, respectively, compared to the clinical plan. The average sparing with the PTV elimination was 2.3, 2.8, 3.0, 5.4, and 6.4 Gy, for the SC, LPG, RPG, LSG, and RSG, respectively, compared to the clinical plan.
Dose de-escalation has the potential to provide additional sparing of the superior constrictor, which is believed to be highly correlated with patient quality of life, compared to elimination of the PTV. The combination of both dose de-escalation and PTV elimination could provide additional sparing.