Primary tumor volume of nasopharyngeal carcinoma: prognostic significance for local control.

PURPOSE: To study the prognostic significance of primary tumor volume on local control of nasopharyngeal carcinoma. METHODS AND MATERIALS: Between 1998 and 2001, 308 consecutive patients with nasopharyngeal carcinoma treated with radical intent were staged with MRI. On the basis of the extent of tumor infiltration outlined by a diagnostic radiologist, the gross tumor volume of the primary and involved retropharyngeal nodes (GTV-P) was delineated by a radiation oncologist for three-dimensional conformal radiotherapy to the nasopharyngeal region using the Helax-TMS Planning System. All patients were treated with 2 Gy daily to a total dose of 70 Gy in 6-7 weeks. Additionally, chemotherapy was given to 128 patients (42%). RESULTS: The median GTV-P for the whole series was 22 cm(3) (range, 1.4-218 cm(3)). Although the GTV-P varied substantially within each T stage, the overall correlation between these two parameters was strongly significant (p <0.01), with the median GTV-P 2.7 cm(3) for T1, 13.2 cm(3) for T2, 28.1 cm(3) for T3, and 65.5 cm(3) for T4. With a median follow-up of 1.9 years (range, 0.1-3.9 years), the 3-year local failure-free rate was 87%. The 3-year local failure-free rate was 97% for patients with a GTV-P <15 cm(3) compared with 82% for those with a GTV-P > or =15 cm(3) (p <0.01). On multivariate analysis (with T stage as a covariate), GTV-P remained an independent prognostic factor for the local failure-free rate (hazard ratio, 1.01; 95% confidence interval, 1.00-1.02; p <0.01). CONCLUSION: Our data suggested that GTV-P is a strongly significant factor for predicting local control of nasopharyngeal carcinoma. The risk of local failure was estimated to increase by 1% for every 1 cm(3) increase in primary tumor volume.