Dosimetric feasibility of sparing the primary site for oropharyngeal squamous cell carcinoma after transoral laser microsurgery in patients with unilateral positive neck nodes.

To quantify the effect of sparing the primary site after transoral laser microsurgery (TLM) for oropharyngeal squamous cell carcinoma (OPSCC).We reviewed 4 patients with OPSCC who were treated with TLM and postoperative radiation. All patients had T1 base of tongue primaries with the following N stages: 1 N1; 2 N2a; and 1 N2b. Three were lateralized to the right and 1 lateralized to the left. The primary site was not spared initially. We created new intensity modulated radiation treatment (IMRT) plans that spared the primary site. The prescribed dose to the high-risk (HR) and standard-risk (SR) planning target volumes (PTVs) was 60 Gy and 46 Gy at 2 Gy/fraction. PTV-SR and PTV-HR were adjusted to exclude the primary site. The primary site was maximally spared while maintaining similar PTV coverage and normal tissue avoidance as the initial plan. Dosimetric comparisons were made between the initial and primary-site sparing IMRT plans.Dosimetric coverage of the PTVs and normal tissues (pharyngeal constrictors, contralateral parotid, etc) were comparable. The mean dose to the primary site was reduced by 20 Gy. The mean dose to the oral cavity was reduced by 25 Gy.This study suggests that omitting the primary site from the radiation therapy target volume is unlikely to reduce long-term swallowing function to a meaningful degree in patients who receive radiation therapy following TLM for base of tongue cancer.