Patterns of Failure After Postoperative Intensity Modulated Radiation Therapy for Locally-Advanced Buccal Cancer

Abstract

Purpose/Objective(s): Squamous cell carcinoma (SCC) of buccal mucosa has a high incidence of locoregional failure. Its aggressive behavior and the change of lymphatic and vascular drainage after surgery make the design of the radiation treatment field difficult. We retrospectively analyzed our treatment results of locally advanced buccal cancer and intended to define the patterns of failure and provide information for the design of a better radiation treatment. Materials/Methods: Between January 2007 and December 2010, 51 patients with histologically confirmed SCC of buccal mucosa underwent surgery followed by postoperative intensity modulated radiation therapy (IMRT). All patients with locally advanced buccal cancer (AJCC stage III, 26 patients, 51%; stage IV, 25 patients, 49%). The high-risk clinical target volume (CTV) covered the surgical tumor bed and ipsilateral or bilateral upper neck. The low-risk CTV was ipsilateral or contralateral lower neck. The median prescribed radiation dose to high-risk CTV was 60 Gy and the median dose to low-risk CTV was 54 Gy. The 29 (57%) patient received bilateral neck irradiation. Ten patients (20%) also received concurrent postoperative chemotherapy with IMRT. Results: The median follow-up was 42 months (range, 6-77 months). Treatment failure occurred in 19 cases as follows: local in 13, ipsilateral neck in 9, contralateral neck in 3, and distant metastasis in 7. Most (90%) of the patients with contralateral neck recurrence or distant metastasis were accompanied with other locoregional recurrences. The median time from treatment completion to first locoregional recurrence was 7.3 months (range, 4.1-34.2 months). Of the 13 patients with local recurrence, 4 presented with perineural spreading into intracranial region and 4 patients with retromolar trigone recurrence. A total of 61.5% local recurrences were involved with infratemporal fossa or masticator space. The estimated 4-year local failure-free survival, locoregional failure-free survival, distant metastasis-free survival, and overall survival rates were 72%, 63.3%, 85.9%, and 68.8%, respectively. Conclusions: SCC of buccal mucosa is a highly aggressive form of oral cavity cancer with a high locoregional failure rate and most locoregional recurrences led to lethal events. Improvement of high-risk CTV definition especially in infratemporal fossa, masticator space, and retromolar trigone might transfer into better locoregional control. Author Disclosure: Y. Lin: None. L. Li-Ching: None.