Prediction of tumor control by tumor regression at 40 Gy/4 weeks of external beam irradiation for oropharyngeal carcinoma.

Purpose: To predict tumor control on the basis of tumor regression at 40 Gy/4 weeks of external beam radiotherapy (EBRT) for oropharyngeal carcinoma.

Methods: From 1990 to 1997, 55 patients (9 Stage I+II, 15 Stage III, and 31 Stage IV) with squamous cell carcinoma of the oropharynx were treated with curative EBRT (median dose, 66 Gy). Tumor response at 4 weeks was compared with loco-regional control.

Results: The five-year loco-regional control rate was 52%. Regression of primary tumors was more rapid and occurred at a rate higher than that of nodal lesions; however, nodal response served as a superior predictor of tumor control. Predictive factors for loco-regional control were tumor stage, loco-regional response at 4 weeks, and pathological differentiation. Stage III and non-well-differentiated stage IV tumors demonstrating >50% regression at 4 weeks were controlled initially at 74% (17/23) and ultimately at 83% (19/23) by salvage therapy. In contrast, stage III+IV tumors displaying <50% regression and well-differentiated stage IV tumors exhibiting >50% regression were controlled initially at 9% (2/23) and ultimately at 22% (5/23).

Conclusion: Tumor regression at 40 Gy/4 weeks of EBRT is an important parameter in terms of prediction of loco-regional control for stage III and IV disease.