PURPOSE: The health care sector is a major contributor of worldwide greenhouse gas (GHG) emissions. Indirect emissions, including those associated with transportation, make up 82% of the US health care sectors environmental footprint. Radiation therapy (RT) treatment regimens present an opportunity for environmental health care-based stewardship owing to the high incidence of cancer diagnosis, significant utilization of RT, and myriad treatment days required for curative regimens. Because the use of short-course RT (SCRT) in the treatment of rectal cancer has demonstrated noninferior clinical outcomes compared with conventional, long-course RT (LCRT), we investigate the environmental and health equity-related outcomes. METHODS AND MATERIALS: Patients treated with curative, preoperative RT for newly diagnosed rectal cancer at our institution between 2004 and 2022 and living in-state were included. Travel distance was estimated using patients reported home address. Associated GHG emissions were calculated and reported in carbon dioxide equivalents (CO2e). RESULTS: Of 334 patients included, the total distance traveled for the treatment course was significantly greater in patients treated with LCRT versus SCRT (median, 1417 vs 319 miles; P < .001). Total CO2e emissions for those undergoing LCRT (n = 261) and SCRT (n = 73) were 665.3 kg CO2e and 149.9 kg CO2e, respectively, per treatment course (P < .001), with a net difference of 515.4 kg CO2e. Relatively, this suggests that LCRT is associated with 4.5 times greater GHG emissions from patient transportation. CONCLUSIONS: Using treatment of rectal cancer as proof-of-principle, we advocate for the inclusion of environmental considerations in the creation of climate-resilient oncologic RT practices, especially in the context of equivocal clinical outcomes between RT fractionation schedules.