Postoperative radiotherapy for malignant tumors of the parotid gland

Purpose: To update our experience using postoperative irradiation in selected patients with carcinomas of the parotid gland. Outcomes of treatment with a focus on the effectiveness of the two primary techniques of radiation used for treating these tumors were evaluated. Methods and Materials: A retrospective analysis of 166 patients with parotid gland malignancies treated in the Department of Radiotherapy at the University of Texas M.D. Anderson Cancer Center between 1965-1989 was performed. All patients were treated following surgery and did not have macroscopic disease at the time of their radiation. The most common histologies were mucoepidermoid carcinoma (28%) and adenocarcinoma (27%). Pathologic features constituting indications for postoperative radiotherapy included: inadequate margins, 104 (63%) cases; extraglandular disease extension, 82 (49%); perineural invasion 57 (34%); and nodal disease 43 (26%). Radiation was delivered through an ipsilateral field of predominantly high energy electrons in 142 patients (86%). Wedged paired ⁶⁰Co fields were used to treat 19 patients. The median dose was 60 Gy, typically delivered at 2 Gy per fraction. The median follow-up time for surviving patients was 155 months. Results: Forty-seven (29%) patients had disease recurrence, of whom 15 (9%) had disease recur locally and 10 (6%) regionally (neck). There was no association between the dose of radiation and local failure, except for a trend for patients with positive margins and/or named nerve involvement to have improved local control if they received doses >60 Gy. There was no difference in failure rates in patients treated with wedged pair techniques or ipsilateral fields, but there was a higher complication rate in the former. Overall, 37 patients (22%) developed chronic sequelae attributed to radiation. Twelve patients developed decreased hearing, and 15 patients developed soft tissue or bone necrosis or exposure. Conclusions: Local and regional control rates for high risk patients with parotid gland carcinomas treated with radiation following surgery were excellent. The technique of using an ipsilateral field encompassing the parotid bed and treated with high energy electrons often mixed with photons was effective with minimal severe late toxicity. The moderate complication rate experienced in this series can be further reduced using modern techniques as described.