2662 - Evaluating Post-Radiation Effects in Meningioma and Glioma Patients: A Proton vs. Photon Therapy Comparison

Purpose/Objective(s): External beam radiation therapy is a standard treatment for meningiomas and gliomas. Proton therapy, an emerging alternative to photon (x-ray) therapy, offers improved normal tissue sparing but may increase post-radiation imaging changes and symptomatic injury due to end-of-range radiobiological effects. This study compares the incidence of radiation-induced brain injury in meningioma and glioma patients treated with proton versus photon therapy.

Materials/Methods: A retrospective review of 61 WHO Grade I (n=30), II (n=29), or III (n=2) meningioma and 53 WHO Grade II (n=30) or III (n=23) glioma patients received either intensity modulated proton therapy (n=30 for meningioma; n=29 for glioma) or photon volumetrically modulated arc therapy (n=31 for meningioma; n=24 for glioma) at a tertiary center, with doses of 50–60 Gy delivered over 25–33 fractions. Post-radiation T1-weighted contrast enhancement (T1CE) or T2/FLAIR changes unrelated to tumor progression were assessed. Symptomatic cases were graded per the Common Terminology Criteria for Adverse Events v5.0.

Results: Meningioma patients treated with proton therapy had a significantly higher incidence of post-radiation imaging changes (14/30 vs. 6/31, p=0.031). Symptomatic cases were more frequent with proton therapy (7/30 vs. 2/31) but did not reach statistical significance (p=0.081). Median follow-up time after radiation was shorter for proton therapy (19.7 vs. 47.2 months). Median time to MRI changes was also shorter for proton therapy (4.5 vs. 7.6 months), while symptomatic effects appeared later (12.2 vs. 7.6 months), suggesting delayed clinical manifestation.

In glioma patients, no significant differences between proton and photon therapy were observed in post-radiation changes (14/29 vs. 14/24, p=0.583) or symptomatic cases (3/29 vs. 7/24, p=0.156). Median follow-up time after radiation was shorter for proton therapy (18.1 vs. 30.1 months). Proton therapy was associated with later MRI changes (5.6 vs. 3.6 months) but shorter time to symptoms (11.7 months vs. 13 months).

Adverse events varied by modality:

? Meningioma-Proton: 2 grade 1, 4 grade 2, 1 grade 3

? Meningioma-Photon: 1 grade 1, 1 grade 3

? Glioma-Proton: 1 grade 2, 2 grade 3

? Glioma-Photon: 1 grade 1, 1 grade 2, 4 grade 3, 1 grade 4

Conclusion: This study indicates that proton therapy may be associated with a higher risk of asymptomatic and symptomatic post-radiation imaging changes for meningioma patients. Differences in follow-up time may impact long-term findings. While proton therapy is beneficial for distant normal tissue sparing, higher biologically effective doses could contribute to increased radiation-induced changes and toxicity.