Adjuvant Radiation Therapy Nodal Target Volumes in Oral Cancer: Do Consensus Guidelines Reflect Patterns of Failure?

Abstract

Consensus guidelines on nodal target volumes in oral cancer intensity-modulated radiotherapy (IMRT) (Chao 2002, Liu 2015, Merlotti 2015) recommend bilateral and lower neck volumes, even in pN0 and lateralized primaries. However clinical practice is varied. We evaluated the patterns of nodal failure following adjuvant IMRT and its correlation with the treated target volumes in a large single institutional series, with special emphasis on contralateral and lower neck failures.Retrospective data of 421 patients treated between 2011 to 2017 with adjuvant IMRT for oral cancer was evaluated. This included data on the site of primary, the level and side of pathological nodal involvement, radiotherapy target volumes, doses delivered to each volume and site(s) of failure. Nodal target volumes were varied and reflected more conservative practice. Patterns of failure were mapped according to the nodal status and site of the primary, oral tongue or gingivobuccal (GB).Nodal target volumes and failures with a median follow-up of 36 months are depicted in Table 1. In terms of contralateral nodal coverage, ipsilateral lower neck treatment and contralateral lower neck treatment 110/254 (43.7%), 111/280 (39.6%), 165/232 (71.1%) patients were treated more conservatively than published guidelines. For pN0 cancers of either oral tongue or gingivobuccal site, the incidence of any contralateral failure or ipsilateral level IV failure was low (0-4%) and independent of inclusion into target volumes. In pN+ cancers of both sites, contralateral failures were more common (5-23%) and were predominantly in the contralateral Ib and II. Contralateral level III-IV failures were very uncommon even in pN+ cancers, especially in GB primaries (< 2%).Patterns of failure, when correlated with treated volumes, suggest that current recommendations may be generous and not reflective of actual patterns of failure. Consideration should be given to sparing of elective contralateral neck and lower neck treatments in pN0 tongue and GB patients, and contralateral lower neck in node-positive lateralized GB primaries.