Room: AAPM ePoster Library
Purpose: Locoregional recurrences occur in 15-50% of head and neck cancer (HNC) patients who receive primary radiation therapy, and salvage surgery is not always feasible. Highly conformal stereotactic body radiation therapy (SBRT) has shown promising outcomes for unresectable localized recurrent HNC (rHNC), but the maximum deliverable tumor dose is limited by toxicity to the surrounding, previously irradiated tissues. It is well known that incorporating highly non-coplanar beam angles can improve dose conformality, and recently available commercial software has made automated non-coplanar VMAT (anVMAT) planning and delivery clinically feasible. This study explores the ability of this new planning technique to escalate the tumor dose in rHNC SBRT plans while minimizing toxicity to adjacent organs-at-risk (OARs).
Methods: Ten rHNC patients from our clinic were selected who were re-irradiated with SBRT to 40 Gy in 5 fractions with mostly partial coplanar arcs. New plans were created using the anVMAT technique to escalate the target dose to 55 Gy while achieving similar or lower OAR doses. Maximum dose constraints were placed on the larynx (=20 Gy), spinal cord (=8 Gy), mandible (=20 Gy), brainstem (=8 Gy), and skin (=36 Gy), while also matching the clinical dose to any other OARs.
Results: anVMAT, using 4 partial non-coplanar arcs for each plan, achieved significant average increases in mean GTV and PTV doses of 14 Gy (34%) and 13 Gy (32%), respectively. Clinically equivalent OAR doses were also achieved, and any OAR doses exceeding constraints were matched or reduced in the anVMAT plans, with 8/10 anVMAT plans meeting the 8 Gy spinal cord constraint compared to 5/10 clinical plans.
Conclusion: Automated non-coplanar VMAT planning enables significant dose escalation for HNC SBRT plans while achieving similar OAR doses, potentially improving the local control and overall survival rates for rHNC patients while limiting the risk of treatment-related toxicity.
Funding Support, Disclosures, and Conflict of Interest: This work is supported in part by Varian Medical Systems through our prospective clinical study (NCT03892720).