A retrospective study was performed on 100 pediatric patients with primary brain tumors treated with PBT. Cerebral microbleeds (CMBs) were diagnosed by examining serial MRIs. The study found that the percentage of patients with CMBs was 43%, 66%, 80%, 81%, 83%, and 81% at 1-year, 2-years, 3-years, 4-year, 5-years, and greater than 5 years from completion of proton radiotherapy.

The majority (87%) of CMBs were found in areas of brain exposed to ≥ 30 Gy. The study concluded that CMBs develop in a high percentage of pediatric patients with brain tumors treated with proton radiotherapy within the first few years following treatment. These findings demonstrate similarities with CMBs that develop in pediatric brain tumor patients treated with photon radiotherapy.