Postoperative intensity-modulated radiotherapy following surgery for oral cavity squamous cell carcinoma: patterns of failure.

Objectives: To review outcomes and analyze the patterns of locoregional recurrence of oral cavity squamous cell carcinoma (OCSCC) treated with surgery and postoperative intensity-modulated radiation therapy (IMRT).

Materials And Methods: All patients with Stage I-IVB OCSCC treated with surgery and postoperative IMRT± concurrent chemotherapy between 2005 and 2010 were evaluated. Patient survival and tumor outcomes were prospectively recorded. Outcome measures were 2 year overall survival (OS), local control (LC), regional control (RC) and distant control (DC). Locoregional recurrences were spatially localized in relation to dosimetric plans.

Results: A total of 180 consecutive patients with median follow-up of 34 months were identified. Disease subsites were oral tongue (46%), floor of mouth (23%), alveolus and hard palate (12%), buccal (9%), retromolar trigone (5%), and lip (4%). The 2 year rates of OS, LC, RC, locoregional control (LRC), and DC were 65%, 87%, 83%, 78% and 83%, respectively. The 2-year estimated rates of LRC for larger subsites were: oral tongue (72%), floor of mouth (84%). Of the 180 patients, 38 (21%) had locoregional failure (LRF). Most LRFs were in-field (26, 68%) with 7 marginal and 5 out-of-field. Marginal/out-of-field failures occurred in the contralateral neck in N2b patients, at high level II/skull base, and in intentionally spared regions (near parotid) of pathologically involved necks.

Conclusions: Nearly a third (12/38) of LR recurrences were marginal or out-of-field following postoperative IMRT for OCSCC. Postoperative IMRT following gross total surgical resection requires careful and comprehensive target volume delineation, and larger volumes may be needed than the primary RT setting.