MEDULLOBLASTOMA - TIME-DOSE RELATIONSHIP BASED ON A 30-YEAR REVIEW

Purpose: Time-dose relationships have proven important in many cancer sites. This study evaluates the time factors involved in the successfu l postoperative radiotherapy of medulloblastoma, based on a 30-year ex perience in a single institution. Methods and Materials: Fifty-three p atients with medulloblastoma received postoperative craniospinal radio therapy with curative intent between 1963 and 1993. Seven patients (13 %) underwent biopsy alone, 28 patients (53%) had subtotal excision, an d 18 patients (34%) had gross total excision. Eleven patients received adjuvant chemotherapy. The mean posterior fossa dose was 53.1 Gy; mos t patients received 54.0 Gy (range, 34.3 to 69.6 Gy). For 41 patients receiving once-a-day therapy, the mean dose was 50.6 Gy (range, 34.3 t o 56.0 Gy). For 12 patients receiving twice-a-day therapy, the mean do se was 61.8 Gy (range, 52.6 to 69.6 Gy). Minimum follow-up was 2 years , and median follow-up was 10.7 years. Survival, freedom from relapse, and disease control in the posterior fossa were calculated using the Kaplan-Meier method, and multivariate analysis was performed for progn ostic factors. Variables related to radiotherapy were examined, includ ing dose to the craniospinal axis, dose to the posterior fossa, fracti onation (once-a-day vs. twice-a-day), use of adjuvant chemotherapy, ri sk group [high (greater than or equal to T3b or greater than or equal to M1) or low (less than or equal to T3a and M0-MX)I, interval between surgery and radiotherapy (excluding patients receiving chemotherapy b efore radiotherapy), and duration of radiotherapy. Results: At 5 and 1 0 years, overall survival rates were 68 and 64%, respectively, and fre edom-from-relapse rates were 61 and 52%, respectively. Rates of diseas e control in the posterior fossa at 5 and 10 years were 79 and 68%, re spectively. At 5 years, absolute survival rates after biopsy alone, su btotal excision, and gross total excision were 43, 67, and 78%, respec tively(p = 0.04), and posterior fossa control rates were 27, 89, and 8 3%, respectively (p 0.004). Duration of the treatment course was the o nly radiotherapy-related variable with a significant impact on freedom from relapse and posterior fossa control. For patients whose radiatio n treatment duration was less than or equal to 45 days, posterior foss a control was 89% at 5 years, compared with 68% for those treated for >45 days (p = 0.01). Duration of treatment also affected freedom from relapse at 5 years: less than or equal to 45 days (76%) compared with >45 days (43%),p = 0.004. Conclusion: Our study demonstrates that if a dequate doses are used, then radiotherapy treatment duration will sign ificantly affect the outcome in terms of control of disease in the pos terior fossa and freedom from relapse. Fractions of at least 1.75 Gy g iven once a day, or a twice-a-day regimen should yield optimal local c ontrol results. (C) 1998 Elsevier Science Inc.