130 - Growth Trajectory following Vertebral Body-Sparing Proton Craniospinal Irradiation in Pediatric Patients
Presenter(s)
K. Daniels1, J. Elster2, S. Sridhar2, M. Paul2, I. MacEwan3, B. Chou4, and K. R. Tringale4; 1UC San Diego, La Jolla, CA, 2Rady Children's Hospital, San Diego, CA, 3California Protons Cancer Therapy Center, San Diego, CA, 4Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, CA
Purpose/Objective(s): Pediatric patients with brain tumors often require craniospinal irradiation (CSI), underscoring the importance of minimizing long-term treatment-related toxicity. Vertebral body-sparing proton CSI (VBSpCSI) minimizes dose to the anterior vertebral bodies while still delivering therapeutic dose to the neuraxis. Although it aims to preserve growth and reduce late effects, concerns about asymmetric sparing leading to spinal deformity (SD) have limited widespread adoption. We sought to characterize spinal growth following treatment and hypothesized that VBSpCSI does not significantly increase early risk of SD.
Materials/Methods: Patients =28 years who received VBSpCSI from 2014-2024 at a single institution were included. Height-for-age percentiles were collected before and at latest follow up after VBSpCSI. SDs were defined clinically or radiographically as abnormal curvature (e.g., scoliosis, kyphosis, lordosis). Cumulative incidence of SD accounting for death as a competing risk was calculated.
Results: 143 patients were included, of whom 99 (69%) had medulloblastoma. The median age at VBSpCSI was 9 years (range 3-28) and median CSI dose was 30.6 Gy (range 12.6–39.6). 2 patients had previously received CSI. Median follow up was 37 months (range 2–133) and median time to last recorded height was 37 months (range 1–132). The median pre-VBSpCSI height percentile was 52.0 (range 0.11–99.7) and the median last post-VBSpCSI height percentile was 25.9 (range 0.01–99.0). Among 114 (80%) patients with both pre- and post-VBSpCSI heights, there was a significant decrease in height percentile (mean change -21.4 percentile points [95% CI -25.4 to -17.5, p<0.001]). 7 patients (4.9%) had a pre-VBSpCSI height percentile < 3%; 22 patients (15.4%) had a post-VBSpCSI height percentile < 3%. 8 patients (6%) developed SD at a median of 22 months (range 3-72). Among this subset, most received a CSI dose of 36 Gy (5/8, 62.5%); the remaining 3 (37.5%) received 23.4 Gy. The cumulative incidence of SD was 2.8% (95%CI 0.1-5.6) at 12 months, 3.9% (95%CI 0.5-7.2) at 36 months, and 6.4% (95%CI 1.6-11.2) at 60 months. Of 33 patients alive and free of SD at 60 months, the cumulative incidence of SD was 4.5% (95%CI 0-13.5%).
Conclusion: This is the largest known study of pediatric patients evaluating growth effects of VBSpCSI. We observed a significant decline in height percentile, suggesting that growth slowing may still occur despite vertebral body sparing. At the same time, VBSpCSI was associated with a relatively low early risk of SD, although longer follow-up is needed given the known delayed onset of deformity (~35% at 15 years). Further study is warranted to better understand other contributors to growth impairment, including radiation dose, systemic therapies, and longitudinal endocrine effects, as well as to determine long-term deformity risk.