Patterns of Care and Referral for Proton Therapy in Breast, Lung, and Prostate Cancer

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We hypothesize that the demographic and clinical characteristics of cancer patients impact the utilization of proton beam therapy (PBT) compared to photon therapy (XRT), even from facilities with access to PBT. We utilized the national cancer database to identify facilities with access to PBT, defined as institutions from which a cancer diagnosis was made and subsequently had at least one patient treated with PBT, between the years 2004 – 2015. We compared the relative usage of XRT and PBT for various demographic and clinical scenarios in breast, prostate, and non-small cell lung cancer (NSCLC) via multivariable binomial logistic regression analysis with odds ratios (OR). In total, 231 facilities with access to PBT accounted for 16,8323 breast, 39,975 lung, and 77,297 prostate cancer patients treated definitively with non-palliative radiotherapy as a component of care. PBT was used in 0.5%, 1.5%, and 8.9% of breast, lung, and prostate cases, respectively. PBT was associated with a farther distance traveled and longer start time from diagnosis for each site (P<0.001). For breast, demographic factors significantly associated with PBT were treatment in the west coast (OR=4.8), age under 60 (OR=1.25), white race (OR=1.94), and metropolitan area (OR=2.8). There was no difference in education level, type of insurance, or income. Left sided cancers (OR=1.28), T1 tumors (OR=1.28), N2 disease (OR=1.71), non-ER+/PR+/Her2Neu- cancers (OR=1.24), accelerated partial breast irradiation (compared to chestwall and whole breast) (OR=1.98), and hypofractionation (OR=2.35) were independent predictors PBT. There was no difference between lumpectomy/mastectomy or boost/no-boost cases. For NSCLC, demographic factors significantly associated with PBT were treatment in the southwest (OR=2.6), metropolitan area (OR=1.72), and Medicare insurance (OR=1.64). There was no difference in education level, gender, race, or income. Higher comorbid score (OR=1.36), later year treated (OR=3.16), and use of hypofractionation compared to conventional fractionation and SBRT (OR=3.7) were independent predictors of PBT. There was no difference in laterality or stage. For prostate, demographic factors significantly associated with PBT were treatment in the west coast (OR=2.48), age under 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=1.84), low risk disease (OR=1.45), definitive compared to postoperative (OR=6.10), and conventional compared to hypofractionation (OR=1.64) were independent predictors of PBT. Even for facilities with established referrals to proton centers, PBT utilization is low, and socio-economic factors can be a barrier to PBT access. PBT was more often used with left-sided breast and low-risk prostate cancers, without a clear clinical pattern in NSCLC cancer.