Reduced‐volume tumor‐bed boost is not associated with inferior local control and survival outcomes in high‐risk medulloblastoma

Background Radiotherapy boost to the entire posterior fossa (PF) is standard of care for high-risk (H-R) medulloblastoma patients; the utility of tumor bed (TB)-only boost is unclear. The purpose of this study was to examine the impact of PF versus TB boost volume on tumor control and survival in the H-R medulloblastoma population. Methods Single-institution records for patients with H-R medulloblastoma were reviewed. The median craniospinal irradiation dose was 36 Gy (range, 23.4-45 Gy), and boost doses to either PF or TB were 54 to 55.8 Gy. PF (local) failures were scored as in-field, marginal (between 80% and 95% isodose lines), or distant. Kaplan-Meier methods and Cox proportional hazards were used to assess the impact of radiation boost technique on local control (LC) and survival endpoints. Results Thirty-two patients with H-R medulloblastoma were treated between 1990 and 2015, with a median follow-up length of 5.12 years. Twenty-two patients received PF boost, and 10 received TB boost. Patient and disease characteristic were comparable between groups. A total of 11 PF failures occurred, including 3 isolated LFs (2 in the PF and 1 in the TB group). Most PF failures were in-field: three of four in the TB group and six of seven in the PF group; the remainder were marginal failures. TB boost was not associated with inferior LC (hazard ratio [HR] 0.86, log-rank P = 0.81) or overall survival (HR 1.40, P = 0.56) compared with PF boost. Conclusion Reduced-volume radiotherapy boost to the TB does not appear to compromise LC or survival in patients with H-R medulloblastoma; it may reduce the risk of ototoxicity.