PATTERNS OF PROTON THERAPY UTILIZATION AND OUTCOMES IN CANADIAN PEDIATRIC PATIENTS

Purpose:

Proton beam therapy (PBT) is a precise radiotherapy modality that minimizes radiation dose to normal tissues compared to photon radiotherapy. Currently, there are no PBT centres in Canada, and Canadian patients must be referred to the United States (US). There is a limited understanding of patterns of PBT utilization and outcomes in Canadian pediatric patients. Our study aims to characterize these patterns and to estimate the survival of patients who receive PBT in the US.

Materials and Methods:

Our study population includes all patients residing in Canada who were enrolled in the Pediatric Proton/Photon Consortium Registry (PPCR), a prospective, multi-institutional registry of pediatric patients treated with PBT. Eligible individuals were age <22 at time of starting treatment, treated between 2012 July 1 and 2024 Sep 1, and received PBT at a PPCR institution. We conducted a descriptive analysis of patient demographics, diagnoses, and time of treatment. We estimated overall survival from time of first proton treatment using the Kaplan-Meier method and compared survival between groups using the log-rank test.

Results:

214 patients were included, 64% male and 36% female. Mean age at diagnosis was 8.6 years (range 0-20). Mean age at first proton treatment was 9.5 years (range 1-21). The primary diagnoses included 143 (66.8%) CNS and 71 (33.2%) non-CNS tumours. The most common CNS histologic subtypes were medulloblastoma (45 [31.5%]), craniopharyngioma (23 [16.1%]), ependymoma (23 [16.1%]), and germ cell (23 [16.1%]). The most common non-CNS tumours were rhabdomyosarcoma (25 [35.2%]), other soft tissue or bone sarcoma (17 [23.9%]), and neuroblastoma (11 [15.5%]). 37 (17.3%) patients had metastatic disease. The number of patients treated per year peaked at 38 in 2019, decreased to 13 in 2020, and then steadily increased to 30 in 2023. The survival analysis included 106 patients with available follow-up data. Five-year overall survival (OS) from time of proton treatment was 76.9% (95% CI: 0.673-0.880) for all patients. Five-year OS in patients with CNS tumours was 85.9% (95% CI: 0.744-0.969) compared to 62.0% (95% CI: 0.450-0.853) in patients with non-CNS tumours (p=0.04). Patients with metastatic disease had inferior OS, with 3-year estimates of 64.7% (95% CI: 0.426-0.982) versus 82.8% (95% CI: 0.738-0.929) for localized tumours (p=0.03).

Conclusions:

This is the first study reporting patient-level data from US proton centres regarding children living in Canada, with data on demographics, diagnoses treated, and survival. Since 2020, the number of patients treated per year has been increasing. Most patients treated with PBT, particularly those with CNS or non-metastatic tumours, remain alive five years after their proton treatment. PBT should continue to be offered as a treatment option for Canadian pediatric patients with curable tumours.