Late Effects of Craniospinal Irradiation Using Electron Spinal Fields for Pediatric Patients

Abstract

<h3>Purpose/Objective(s)</h3> Craniospinal irradiation (CSI) with photons is associated with significant toxicities. The use of electrons for spinal fields is hypothesized to spare anterior structures but its long-term effects remain poorly characterized. We studied late effects of CSI using electrons for spinal radiotherapy (RT). <h3>Materials/Methods</h3> Records of 84 consecutive patients treated with CSI using electrons for the spine at a single institution from 1983-2014 were reviewed. Median age at RT was 5 (range, 1-14) years with 60% male. Most common histologies were medulloblastoma/PNET (59%) and ependymoma (8%). Most commonly used electron energies were 16 (44%) and 20 (25%) MeV (range, 12-21). Median prescribed dose to the entire spine was 30 (range 6-45) Gy. A spinal boost was used in 14%. A subset of 47 (56%) patients was analyzed for late effects with the following inclusion criteria: 1) age between 2 and 14 years at time of CSI, and 2) clinical and radiographic follow-up for ≥ 5 years. Height <b>z</b>-scores adjusted for age before and after CSI were assessed using CDC stature-for-age charts and compared with a <b>t</b>-test. A Cobb angle of > 10° was used to identify scoliosis. <h3>Results</h3> At a median follow-up of 18 (range, 0-37) years, the median survival was 22 (95% confidence interval [CI], 12-28) years with 50 patients (60%) alive at last follow up. On subset analysis for late effects, 18 (38%) patients developed hypothyroidism and 4 (9%) developed secondary malignancies possibly attributable to spine RT (3 papillary thyroid cancer, 1 renal cell carcinoma) at a median 26 (range, 10-33) years after RT. Chronic pulmonary issues were seen in 2 patients (restrictive lung disease, recurrent pneumonia) and 1 patient developed esophageal strictures and periaortic hemorrhage. No patients developed myelopathy or cardiotoxicity. Median height <b>z</b>-score prior to treatment was -0.3 (37^th percentile; interquartile range [IQR], -1.0 to +0.1) and at last follow up after RT was -2.2 (1^st percentile; IQR, -3.1 to -1.5; <b>P</b> < 0.001). Of 42 patients with spinal curvature assessments, 14 (33%) had scoliosis with median Cobb angle 16° (IQR, 14-18°). <h3>Conclusion</h3> Long-term follow-up of children treated with CSI using electron spinal fields showed frequent musculoskeletal toxicity, predominantly decreased height. Scoliosis and hypothyroidism were seen in at least a third of long-term survivors. Esophageal, pulmonary, cardiac and spinal cord toxicities were infrequent.