Short-course radiation for prostate and breast cancer: An analysis of practice across Washington State 2020-2023.

462 Background: Shortened (hypofractionated, HF) radiation (RT) courses reduce clinical, social and financial toxicities of treatment. We aimed to assess factors associated with HF RT in Washington State (WA). Methods: A retrospective cohort study of patients (pts) with non-metastatic prostate or breast cancer treated with RT 2020-2023. Cancer registry data was linked to private/public claims and RT fractions (fx) were defined as ultra-HF (UHF = 1-7 fx prostate, 5-12 fx breast), HF (8-30 fx prostate, 13-24 fx breast) and conventional (CF = 31-50 fx prostate, 25-40 fx breast). Multivariable multinomial logistic regression assessed factors associated with HF / UHF compared to CF. Results: Of 1,963 pts with prostate cancer and 3,966 with breast cancer, most were ≥ 65 years old (prostate 80%; breast 51%), non-Hispanic white (prostate 86%; breast 81%), and resided in urban areas (prostate 81%; breast 87%). Of prostate pts, 15%/51%/34% were AJCC8 stage I/II/III, respectively. In the breast cohort, 15%/69%/16% were stage 0 (DCIS)/I/II-III, respectively. Older pts and those in rural areas were more likely to receive HF. Adjusted odds of UHF and HF increased over time, though more markedly in breast cancer (Table). The proportion of breast UHF regimens using complex intensity-modulated RT (IMRT) increased from 2% in 2020 to 60% in 2023. Pts with Medicare were less likely to receive HF (but not UFH) for both cancers, while pts with Medicaid were less likely to receive both HF and UFH for breast cancer (Table). Conclusions: Hypofractionated RT, especially complex ultra-short breast RT, has become more common in WA. Consistent with national data, pts with Medicaid receive longer RT courses for breast cancer. Further research should explore system and clinician factors associated with HF to facilitate adoption, especially for patients with fewer resources. PROSTATE BREAST HF aOR 2 (95% CI) UHF aOR (95% CI) HF aOR (95% CI) UHF aOR (95% CI) Age (per 5-yr increase) 1.13 (1.04–1.23) 0.94 (0.85–1.05) 1.20 (1.14–1.26) 1.31 (1.21–1.43) Insurance Commercial Ref Ref Medicare 0.62 (0.44–0.86) 0.68 (0.47–1.00) 0.72 (0.55–0.95) 0.68 (0.44–1.03) Medicaid 1.33 (0.75–2.36) 0.60 (0.30–1.21) 0.52 (0.40–0.68) 0.57 (0.35–0.92) Rural-Urban Commuting Area Urban Ref Ref Rural 2.41 (1.82–3.18) 1.85 (1.33–2.57) 1.56 (1.18–2.06) 1.55 (1.04–2.31) Stage 0 6.43 (4.19–9.87) 5.27 (3.15–8.84) I Ref Ref II 1 0.97 (0.70–1.34) 0.79 (0.56–1.10) 0.22 (0.18–0.27) 0.19 (0.13–0.29) III 0.37 (0.26–0.52) 0.18 (0.12–0.27)