Real-World Experience Using Proton Versus Photon Craniospinal Irradiation for Leptomeningeal Disease.

PURPOSE: Data demonstrate improved survival with proton craniospinal irradiation (CSI) over involved field radiation therapy for leptomeningeal disease (LMD). It is unknown how photon CSI compares in the treatment of LMD. We report our institution's real-world experience using proton versus photon CSI for LMD.

METHODS AND MATERIALS: We performed a retrospective review of LMD patients treated with photon or proton CSI from January 2021 to February 2024. All histologies were included. Patient characteristics and complete blood counts were collected before and after CSI. The primary endpoint was serious cytopenia likely caused by CSI. The median overall survival was estimated using the Kaplan-Meier method.

RESULTS

Thirty-six patients with LMD treated with CSI (27 proton and 9 photon) were included. Across all major cell lines (hemoglobin, platelets, leukocytes, neutrophils, and lymphocytes), the rate of serious (grade 3 or higher) cytopenia likely caused by CSI was not different between the proton and photon groups (p > .21). The median overall survival in the proton and photon groups was 3.0 months and 1.7 months, respectively (hazard ratio, 1.49; p = .47).

CONCLUSIONS

In a single-institutional experience treating LMD, acute cytopenias likely caused by CSI were not different between proton and photon CSI across all major cell lines. Survival was also similar between modalities; therefore, photon CSI may be a safe, efficacious option for LMD.