Adjuvant radiation in the TORS era: Is there a benefit to omitting the tumor bed?

Abstract

Purpose: Trans-oral robotic surgery (TORS) followed by adjuvant radiation therapy (RT) is becoming popular in treating node-positive tonsillar squamous cell carcinoma (SCC). One potential benefit is eliminating irradiation of the primary site when the tumor is widely resected, and targeting the neck only. This study assessed whether omitting the tumor bed provides any dosimetric or clinical advantage.

Methods and materials: We identified 21 patients with primary tonsillar SCC that were treated with TORS followed by RT to the ipsilateral neck and primary (N+P) site. We subsequently replanned each case to allow target coverage to the neck only, excluding the tumor bed. For each case, we created 2 plans: neck only (NO) and N+P. Additionally, we identified patients (n = 7) with primary SCC tonsil who did receive NO irradiation to compare their dosimetry and toxicity profile with those treated to both the primary site and ipsilateral neck. Contralateral neck radiation was not administered in any of these cases.

Results: Despite excluding the primary site in the NO plans, the mean dose to the tumor bed was high: 53.9 Gy. The only significant differences in omitting the primary site were lower doses to the oral cavity, 29.8 Gy in NO plan versus 34.6 Gy in N+P plan, P = .002, and superior constrictors, 42.9 Gy in NO plan versus 46.1 Gy in N+P plan, P = .01. No appreciable differences in toxicities were noted in the limited cohort treated with NO irradiation.

Conclusions: Sparing the primary site after TORS in node-positive tonsillar SCC does not appear to provide any significant dosimetric or clinical advantage. Furthermore, the tumor bed receives a significant but potentially subtherapeutic dose, limiting options for irradiation in a salvage setting. At this time, we do not recommend omitting the tumor bed from the radiation target volume following TORS.