Oropharyngeal Cancer Treated With Transoral Surgery (Tos) And Radiation Therapy To The Neck With Omission Of The Primary Site: A Radiation Therapy Dosimetric Analysis

Oropharyngeal cancer (OPC) has been treated historically with either radiation therapy (RT) or open surgery. With the advent of transoral surgery (TOS), it has gained in popularity for treatment of OPC. The addition of adjuvant treatment further improves local control, although it results in additional morbidity. In the era of human papillomavirus (HPV)-related cancer, deintensification of therapy is a major consideration. The majority of patients (pts) with OPC have indications for RT due to the presence of neck disease. We report on the outcomes of HPV-related OPC pts that underwent adjuvant RT with omission of the primary site from the clinical target volume (CTV). We identified for the present institutional review board–approved analysis a subset of 40 pts treated at a single institution with TOS followed by neck only RT with exclusion of the primary site. These were favorable risk patients with negative margins, needing RT secondary to risk factors in the neck: multiple positive lymph nodes (LNs), LN >3 cm, and/or extracapsular extension. Thirty eight pts (95%) had transoral laser microsurgery, 24 pts (60%) had base of tongue, and 16 pts (40%) had tonsillar tumors. The majority of the pts (70%) were documented to be HPV + and had T1 N2b disease. T Stage distribution was as follows: T1, 27 pts (67%); T2, 12 pts (30%); and T3, 1 pt (3%). N stage was as follows: N1, 4 pts (10%); N2a, 4 pts (10%); N2b, 27 pts (67%); and N2c, 5 pts (13%). Therefore, 90% of pts had N2 disease, and 23 pts (57%) received concurrent chemotherapy. For all pts, a CTV of the primary surgical bed was contoured to obtain the estimated incidental dose to the primary site. The median follow-up for surviving patients was 51 months (range, 13 – 155 months). The median RT dose to the neck was 6000 cGy (5400 – 6400 cGy). The mean incidental dose to the primary tonsillar site was 4320 cGy (SD, ± 480 cGy) and to the primary base of tongue site was 4060 cGy (± 420 cGy). The mean dose to the constrictors was 4414 cGy (± 648 cGy), to the oral cavity 2170 cGy (± 230 cGy), and to the contralateral parotid 1980 cGy (± 224 cGy). There were no local failures and only one regional failure, resulting in 97.5% locoregional control. Two pts developed distant metastatic disease, without evidence of locoregional recurrence, for a 4-year overall survival of 90%. Dysphagia was reported as Radiation Therapy Oncology Group (RTOG) Grade ≥2 in 5 pts (12%). Only 1 patient was PEG-tube dependent at 1 year, but none were at the last follow-up. Xerostomia was reported as RTOG Grade ≥2 in 7 pts (17%) and oral mucositis as Grade ≥2 in 4 pts (10%). Our analysis suggests that adjuvant RT to the neck only with omission of the primary site after TOS in OPC may be appropriate, in well-selected patients. This treatment approach yields comparable oncologic and improved functional outcomes. Further study is required to validate these findings on a prospective basis and to ascertain whether RT dose can be decreased even more through modalities such as proton beam therapy.