2955 - Review of a Proton Therapy Consultation Service for Radiation Oncologists in Canada

Purpose/Objective(s): Canada is the only G7 country without a clinical proton beam therapy (PBT) facility. While patients can access publicly-funded PBT through out-of-country approval programs, there are still significant barriers to care. Our institution created a national proton therapy consultation service, which allows oncologists to request the creation of a proton plan for their patient and their tumor. The goal of this service was to inform health care providers regarding the potential benefits of proton therapy. The aim of this study was to review all patients referred to our institution’s proton consultation service.

Materials/Methods: We reviewed all patients referred to our proton consultation service from its inception in June 2020 to December 2024. Pencil beam scanning proton plans were generated in the treatment planning system. Photon plans were generally provided by the referring physician. All available photon and proton plans were reviewed. Key dosimetric parameters of both plans were reported for each patient and evaluated using paired t-tests. Mean values are reported, unless otherwise specified.

Results: A total of 55 patients were referred to our service, and 49 had analyzable proton plans. The median patient age at referral was 36 (range, 3-74 years), and 29% of patients were under 18 years of age. Most patients resided in Ontario (89%), and the remainder were from BC, SK, QC, NS, and PE. Reasons for referral included young age, organs-at-risk near a tumor target, re-irradiation, and patient preference for protons. Fifteen patients were ultimately treated with proton therapy; 14 received publicly-funded care in the US, while one additional patient self-funded their own proton treatment in India. Target coverage was similar in both photon and proton plans (CTV V95% photon 97%, proton 98%; p=0.71). For cranial targets (n = 19), there was a statistically significant reduction in the mean brain dose (photon 1049cGy, proton 725cGy; p<0.001), mean brain dose minus PTV (photon 676cGy, proton 480cGy; p<0.001), and brain D50% (photon 647cGY, proton 199cGY; p<0.001). There was no statistical difference in brain V50% (p=0.28). For targets in the thorax (n = 7), there was a statistically significant reduction in the mean lung dose (photon 1172cGy, proton 864cGy; p=0.02), lung V50% (photon 21%, proton 18%; p=0.02), and lung D50% (photon 978cGy, proton 603cGy; p=0.02) with proton therapy. There was no difference in lung D2% (p=0.69).

Conclusion: Our proton consultation program provides an important service by demonstrating the dosimetric differences between PBT and photon therapy and contributed towards a third of referred patients to ultimately going to the US for PBT.