Methodological guide for assessing the carbon footprint of external beam radiotherapy: A single-center study with quantified mitigation strategies.

Background and purposes: Data on the carbon footprint of external beam radiotherapy (EBRT) are scarce. Reliable and exhaustive data, including a detailed carbon inventory, are needed to determine effective mitigation strategies. Materials and methods: This study proposes a methodology for calculating the carbon footprint of EBRT and applies it to a single center. Mitigation strategies are derived from the carbon inventory, and their potential reductions are quantified whenever possible. Results: The average emission per treatment and fraction delivered was 489 kg CO₂eq and 27 kg CO₂eq, respectively. Patient transportation (43 %) and the construction and maintenance of linear accelerators (LINACs) and scanners (17 %) represented the most significant components. Electricity, the only energy source used, accounted for only 2 % of emissions.Derived mitigation strategies include a data deletion policy (reducing emissions in 30 years by 12.5 %), geographical appropriateness (-12.2 %), transportation mode appropriateness (-9.3 %), hypofractionation (-5.9 %), decrease in manufacturers' carbon footprint (-5.2 %), and an increase in machine durability (-3.5 %). Conclusion: Our findings indicate that a significant reduction in the carbon footprint of a radiotherapy unit can be achieved without compromising the quality of care.This study provides a methodology and a starting point for comparison and proposes and quantifies mitigation strategies, paving the way for others to follow.