Delivery of re-irradiation and complex palliative radiotherapy using proton therapy in pediatric cancer patients

Background: The intent of this study is to characterize indications for pediatric palliative-intent proton radiation therapy (PIPRT). Procedure: We retrospectively reviewed patients 21 years and younger who received PIPRT. We defined PIPRT as radiotherapy (RT) aimed to improve cancer-related symptoms/provide durable local control in the non-curative setting. Mixed proton/photon plans were included. Adjacent re-irradiation (reRT) was defined as a reRT volume within the incidental dose cloud of a prior RT target, whereas direct reRT was defined as in-field overlap with prior RT target. Acute toxicity during RT until first inspection visit was graded according to the Common Terminology Criteria for Adverse Events. The Kaplan–Meier method, measured from last PIPRT fraction, was used to assess progression-free survival (PFS) and overall survival (OS). Results: Eighteen patients underwent PIPRT between 2014 and 2020. Median age at treatment start was 10 years [2–21]. Median follow-up was 8.2 months [0–48]. Treatment sites included: brain/spine [10], abdomen/pelvis [3], thorax [3], and head/neck [2]. Indications for palliation included: durable tumor control [18], neurologic symptoms [4], pain [3], airway compromise [2], and great vessel compression [1]. Indications for protons included: reRT [15] (three adjacent, 12 direct), craniospinal irradiation [4], reduction of dose to normal tissues [3]. Sixteen experienced grade (G) 1–2 toxicity; two G3. There were no reports of radionecrosis. Median PFS was 5.3 months [95% confidence interval (CI): 2.7–16.3]. Median OS was 8.3 months [95% CI: 5.5–26.3]. Conclusions: The most common indication for PIPRT was reRT to provide durable tumor control. PIPRT appears to be safe, with no cases of high-grade toxicity.