Nasopharyngeal carcinoma: Repeat treatment with conformal proton therapy - Dose-volume histogram analysis

PURPOSE: To analyze control, survival, and complication rates of conformal proton radiation for recurrent nasopharyngeal carcinoma. MATERIALS AND METHODS: Sixteen patients with nasopharyngeal carcinoma initially treated with 50.0-88.2 Cy photons were re-treated with protons to additional doses of 59.4-70.2 CGE. Local-regional control and survival were correlated with extent of relapse, recurrence versus persistence, and prescribed dose and were subjected to dose-volume histogram analysis. Mean follow-up was 23.7 months (range, 4-47 months). RESULTS: Twenty-four-month actuarial overall and local-regional progression-free survival rates were both 50%. The 24-month actuarial overall survival rates for patients with "optimal" dose-volume histogram coverage versus "suboptimal" coverage were 83% and 17%, respectively (P =.006). Doses to critical structures were low (0-22.0 Gy); no central nervous system side effects supervened. CONCLUSION: Adequate tumor coverage, as evaluated by using dose-volume histogram analysis, was found to be the most important variable influencing local-regional control and survival. No central nervous system complications were observed; increases in the dose to adjacent critical structures are being evaluated.