Differences in Patterns of Care and Referral Between Proton and Photon Therapy

To report demographic and clinical characteristics of patients who were more likely to receive proton beam therapy (PBT) than photon therapy from facilities with access to proton centers. We utilized the national cancer database to identify the facilities with access to PBT between 2004 and 2015 and compared the relative usage photons and PBT for demographic and clinical scenarios in breast, prostate, and non-small cell cancer (NSCLC). In total, 231 facilities with access to proton centers accounted for 168,323 breast, 39,975 lung, and 77,297 prostate cancer patients treated definitively. PBT was used in 0.5%, 1.5%, and 8.9% of breast, lung, and prostate cases. PBT correlated with a farther distance traveled and longer start time from diagnosis for each site (p<0.05). For breast, demographic correlates of PBT were treatment in the west coast (OR=4.81), age <60 (OR=1.25), white race (OR=1.94), and metropolitan area (OR=1.58). Left sided cancers (OR=1.28), N2 (OR=1.71), non-ER+/PR+/Her2Neu- cancers (OR=1.24), accelerated partial breast irradiation (OR=1.98), and hypofractionation (OR=2.35) were predictors of PBT. For NSCLC, demographic correlates of PBT were treatment in the south (OR=2.6), metropolitan area (OR=1.72), and Medicare insurance (OR=1.64). Higher comorbid score (OR=1.36), later year treated (OR=3.16), and hypofractionation (not SBRT) (OR=3.7) were predictors of PBT. For prostate, correlates of PBT were treatment in the west coast (OR=2.48), age <70 (OR=1.19), white race (OR=1.41), metropolitan area (OR=1.25), higher income/education (OR=1.25), and treatment at an academic center (OR=33.94). Lower comorbidity score (OR=1.42), later year treated (OR=1.37), low risk disease (OR=1.45), definitive compared to postoperative (OR=6.10), and conventional fractionation (OR=1.64) were predictors of PBT. Even for facilities with established referrals to proton centers, PBT utilization was low; socio-economic status was potentially a factor. PBT was more often used with left-sided breast and low-risk prostate cancers, without a clear clinical pattern in lung cancer.