Intensity-modulated radiation therapy for oropharyngeal carcinoma: Impact of tumor volume

Purpose To assess the therapeutic outcomes in oropharyngeal cancer patients treated with intensity-modulated radiotherapy (IMRT) and analyze the impact of primary gross tumor volume (GTV) and nodal GTV (nGTV) on survival and locoregional control rates. Methods and materials Between February 1997 and September 2001, 74 patients with squamous cell carcinoma of the oropharynx were treated with IMRT. Thirty-one patients received definitive IMRT; 17 also received platinum-based chemotherapy. Forty-three patients received combined surgery and postoperative IMRT. The median follow-up for all patients was 33 months (range, 9-60 months). Fifty-two patients (70.3%) had Stage IV disease, 17 patients (23%) had Stage III, 3 patients (4.1%) had Stage II, and 2 patients (2.7%) had Stage I tumors. The mean prescription dose was 70 and 66 Gy, respectively, for the definitive and postoperative cohorts. The daily fraction dose was either 1.9 or 2 Gy, five times weekly. The GTV and/or nGTV were determined and derived using the Computational Environment for Radiotherapy Research, a free software package developed at Washington University. The mean GTV was 30.5 ± 22.3 cm³, and the mean nGTV was 23.2 ± 20.6 cm³. Results Ten locoregional failures were observed. Six patients died of disease and three died of concurrent disease. Distant metastasis developed in 6 patients. The 4-year estimate of overall survival was 87%, and the 4-year estimate of disease-free survival was 81% (66% in the definitive vs. 92% in the postoperative RT group). The 4-year estimate of locoregional control was 87% (78% in the definitive vs. 95% in the postoperative RT group); the 4-year estimate of distant metastasis-free survival was 90% (84% in the definitive vs. 94% in the postoperative group). Multivariate analysis showed that GTV and nGTV were independent risk factors determining locoregional control and disease-free survival for definitive oropharyngeal IMRT patients. The worst late toxicities documented were as follows: 32 patients with Grade 1 and 9 with Grade 2 xerostomia; 2 with Grade 1 and 1 with Grade 2 skin toxicity; 3 with Grade 1 late mucositis; and 3 with Grade 1 trismus. Seventeen patients required gastrostomy tube placement. Conclusion IMRT is an effective treatment modality for locally advanced oropharyngeal carcinoma. The GTV and nGTV are the most important factors predictive of therapeutic outcome.