KEY POINTS
- This single-centre retrospective study included 25 patients aged 0–18 years with medulloblastoma who received proton therapy between 2018 and 2025. Median age at diagnosis was 7 years, and median follow-up was 41 months.
- Twenty-one patients received proton therapy at initial diagnosis and four at relapse. Treatment included craniospinal irradiation followed by a focal boost, generally to a total dose of 50.4–54.0 Gy(RBE); both passive scattering and active scanning were used.
- New MRI abnormalities not attributable to progression developed in 4 of 25 patients (16%). All four events were grade 1 and asymptomatic, with no grade 2 or higher brain injury detected.
- The estimated probability of remaining free from radiographic brain injury at one year was 83.8% (95% CI 62.4–93.6%). Lesions appeared 4–12 months after the final irradiation.
- All four affected patients had received high-dose chemotherapy, compared with eight of 21 patients without brain injury. High-dose chemotherapy was significantly associated with injury development (p = 0.039).
- Higher craniospinal irradiation doses above 23.4 Gy showed a near-significant association with injury (p = 0.053), while affected patients also received more intrathecal chemotherapy: median 6.5 versus 2 injections (p = 0.069).
- Every radiographic lesion arose within a region receiving at least 45.4 Gy. One lesion resolved spontaneously, while three remained visible at last imaging; none required corticosteroids or other treatment.
CLINICAL TAKEAWAY
No symptomatic brain injury was observed, which is reassuring for pediatric proton therapy. However, the clustering of MRI changes among children receiving high-dose chemotherapy and intensified craniospinal irradiation suggests that cumulative treatment intensity—not proton therapy alone—may increase CNS vulnerability. The result is hypothesis-generating because only four events occurred and chemotherapy intensity was closely linked to radiation dose.