Purpose: Proton beam therapy is often utilized for patients with meningioma given its ability to achieve a lower integral brain dose compared to photon therapy. However, it is unclear whether rates of brain injury are different due to uncertainties in end of range effects. The purpose of this study is to characterize and compare rates of brain injury after proton or photon therapy.

Materials/Methods: We retrospectively reviewed 38 consecutive patients treated with proton therapy from 2014-2017 and 39 patients treated with photon therapy from 2008-2018 from two separate academic institutions. Patients with previous radiation therapy or less than 3 months follow up were excluded. Radiation induced brain injuries were categorized into white matter lesions (WML) defined as newly detected abnormal T2 signal intensities, or radiation necrosis (RN) defined as newly detected abnormal T2 and T1 post contrast signal intensities. Follow up imaging was reviewed by an experienced neuro-radiologist and radiation oncologist. Abnormal MRI scans were then reviewed after fusion with initial radiation plans. Toxicity was graded as per the common terminology criteria for adverse events (CTCAE v4.03).

Results: Median follow-up time was 17.5 months for proton and 24 months for photon therapy. There was no significant difference between the groups for WHO grade, radiation dose, clinical target volume (CTV), history of diabetes, or history of stroke. The median dose in the proton group was 54 CGE (Cobalt Gray Equivalent) in 30 fractions (range: 50.4-60 CGE) and in the photon arm 54Gy in 27 fractions (range: 50.4-61.4 Gy). Nine patients on the photon group received an additional 7.5-9Gy radio-surgical boost. In the proton group, 23 patients were treated with pencil beam scanning and 15 with uniform scanning. The cumulative incidence of WML at 2 years was 34.2% after proton and 48.7% after photon therapy (p=0.20). The cumulative incidence of RN at 2 years was 18.4% after proton and 2.6% after photon therapy (p=0.02). In the proton group, grade ≥2 was recorded in 3 patients and one patient had a grade 4/5 event. In the photon group, grade ≥2 was recorded in only one patient.


Conclusion: Patients treated with either proton and photon beam therapies have high rates of developing parenchymal T2 signal intensity abnormalities. However, in our series, patients were more likely to develop parenchymal T1 post-contrast abnormalities after proton therapy. Further study into strategies to decrease risk of brain injury may be warranted to optimize treatment for meningioma patients.

03 - Radiation Induced Brain Injury in Meningioma Patients Treated with Proton or Photon Therapy