Level IB Nodal Exclusion in Oropharyngeal Carcinomas Treated with Radiation Therapy: Safety, Efficacy, and a New Standard of Care in this Patient Population

Abstract

In irradiated oropharyngeal cancers (OPC), risk of chronic xerostomia correlates with volume and total dose to the treated salivary gland tissue. Surgical series published recently help identify patients at increased risk for occult disease at level IB; however, definitive radiation therapy data on the practice is sparse. In cases with low risk of occult disease at level IB, unilateral or bilateral submandibular gland (SMG) sparing radiation therapy could decrease the risk of chronic xerostomia. For over a decade, we have utilized this technique in early stage and locally advanced OPC. All OPCs treated with definitive SMG sparing radiation therapy between January 2010 and December 2015 were reviewed. Level IB, unilaterally or bilaterally, was negative on physical exam and imaging. Patients were excluded if they had prior head and neck irradiation, distant metastases, or neck dissection prior to radiotherapy. Median follow up was 2 years. Inclusion criteria were met in 126 patients. Via IMRT, 90 (73%) received bilateral SMG sparing therapy while 36 (28.5%) had unilateral glands spared. One hundred four men and 22 women were included. Median age was 61. Primary site included 43% tonsil, 51% base of tongue, and 6% other/overlapping. Staging was per AJCC 7th edition. There were 13 (10.3%) T1, 49 (38.89%) T2, 31 (29.4%) T3, and 33 (26.19%) T4. There were 17 (13.4%) N0, 12 (9.5%) N1, 4 (3.2%) N2a, 55 (43.6%) N2b, 33 (26.2%) N2c, and 5 (3.9%) N3. 58% were HPV positive. The most common stage was IVA (77.5%). At 2 years, overall survival was 85.7% and 29 patients recurred (23%). 9 were loco-regional (LR) recurrences (7.1%), and 20 were distant (15.8%). LR control rate was 93%. 2 patients relapsed at level IB (1.6%), one of each in the bilateral and unilateral groups respectively. Median time to recurrence was 10 months. Of the relapses, 89.6% of them were node positive before treatment, 58.62% were T3/T4, and 55.2% were HPV positive. The bilateral sparing group had more overall recurrences, but included a larger number of patients; LR relapse were equal (4 bilateral vs 5 unilateral). This retrospective review of level IB sparing radiation therapy for early stage and locally advanced OPC demonstrates safety and efficacy at 2 years, during which most recurrences are likely to occur. To our knowledge, this is the largest SMG sparing study reported to date, and the oncologic results, in terms of LR control and survival, are comparable to previously published outcomes with level IBs treated. Since multiple studies have shown that SMG sparing radiation therapy decreases rates of chronic xerostomia, exclusion of level IB nodal basins in OPC should be considered in all cases without clinical or radiologic involvement of IB. Longer follow-up is indicated, and we plan to report long term outcomes in the future.