Incidence and Dosimetric Parameters of Brainstem Toxicity in Pediatric Patients after Photon Irradiation for Posterior Fossa Tumors

Abstract

<h3>Purpose/Objective(s)</h3> Radiation therapy (RT) is a crucial component of multimodal therapy for central nervous system (CNS) tumors in pediatric patients. Brainstem necrosis is a serious complication of radiotherapy, and currently, data on the incidence of and factors that predict brainstem necrosis after photon therapy to posterior fossa tumors remain lacking. To better understand the true incidence of brainstem injury and the appropriate dosimetric guidelines to limit this adverse event after photon irradiation, we investigated pediatric patients who received photon irradiation to the brainstem for primary tumors at our institution to determine the incidence and associated predictors of brainstem toxicity. <h3>Materials/Methods</h3> Retrospective chart review was conducted for 74 pediatric patients who were treated with photon radiotherapy for posterior fossa tumors from 2000-2016. Patients were excluded if they received a maximum dose to the brainstem <50.4 Gy or had tumor with brainstem involvement. Central imaging review of all MRI scans pre- and post-radiation were reviewed. Brainstem toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 5. <h3>Results</h3> Median clinical and imaging follow-up after completion of first radiation treatment was 4.2 years (Range: 0.1-12.7) and 4.0 years (range: 0.1-12.7). Median age at diagnosis was 8.0 years (range: 0.25-19.8). Most of the patients were treated for medulloblastoma (69.3%) and ependymoma (22.7%). Median prescribed total dose was 54.0 Gy (range: 50.4-59.4), median D50% to the brainstem was 55.6 Gy (range: 12.7- 61.9), and median brainstem V50 Gy and V55 Gy were 97.0% (range: 5.7-100) and 68.6% (range: 0-100), respectively. D1cc to the brainstem was 56.8 Gy (range: 50.8 – 64.9 Gy). The crude incidence rate of grade ≥1 brainstem necrosis was 5.4% (4/74), and grade ≥2 brainstem necrosis was 2.7% (2/74). No clinical, treatment or dosimetric variables were associated with patients with brainstem necrosis or brainstem toxicity. <h3>Conclusion</h3> These data suggest that photon therapy leads to low rates of brainstem necrosis. Future studies with longer follow-up are necessary to further examine the rates of brainstem toxicity, including necrosis, after photon and proton radiotherapy, and larger cohort studies are needed to identify variables that may predict toxicity as these events remain rare.