Level I evidence.
Top Line: Irradiation of level IB obliterates the submandibular gland, a critical contributor to unstimulated saliva.
The Study: So we should think long and hard about when we really need to include it in our radiation volumes. This retrospective review of patients with nasopharyngeal cancer with high risk for level Ib microscopic disease (read: level IIA nodal disease ≥2 cm and / or extracapsular extension) compared outcomes across 169 propensity score-matched pairs who did versus did not have level IB targeted. The rate of level Ib failure at a median follow-up of nearly 10 years was 1.2% after level Ib-irradiation versus 1.8% without. As expected, there was also no significant difference in other disease and survival outcomes. However, the incidence of any dry mouth at 5 years was higher after level Ib-irradiation (28%) than without (17%). Another study back in 2021 performed a detailed analysis of cervical lymph node level involvement. Ib was infrequently involved with a higher risk when an adjacent level and multiple other levels were involved.
TBL: This retrospective study suggests that omitting elective coverage of level IB for node positive NPC results in a low risk of IB failure while decreasing the rate of xerostomia. | Wang, Radiother Oncol 2022