The carbon footprint of external beam radiotherapy and its impact in health technology assessment

•A typical radiotherapy treatment emits from 185 to 2066 kgCO2eq in France.•CO2eq emissions are mostly driven by accelerator acquisition and maintenance as well as patients and workers rides.•Hypofractionation has a strong impact on mitigating carbon footprint.•Hypofractionation related toxicities are usually lower than damages avoided to future people thanks to CO2eq mitigation. The major drivers of carbon dioxide (CO2eq) emissions of external beam radiation therapy (EBRT) are not well known and limit our ability to initiate mitigation strategies. We describe the carbon footprint of four typical centers. We explore direct EBRT associated factors such as the impact of fractionation and use of MRI-LINAC, as well as indirect factors (e.g. patient rides). Treatment strategy related CO2eq emissions are included in a health technology assessment analysis that takes into account CO2eq emissions. A typical EBRT treatment emits from 185 kgCO2eq to 2066 kgCO2eq. CO2eq emissions are mostly driven by (i) accelerator acquisition and maintenance (37.8 %), (ii) patients and workers rides (32.7 %), (iii) drugs and medical devices (7.3 %), (iv) direct energy consumption (6.1 %), and (v) building and bunker construction (5.6 %) with a substantial heterogeneity among centers. Hypofractionation has a strong impact to mitigate emissions. MRI-LINAC is associated with a substantial increase in CO2eq emissions per fraction and requires ultra hypofractionation in 5 fractions to achieve a similar carbon footprint compared to 20 fractions treatment schemes. The expected limited small increase in toxicities due to hypofractionation (when existing) are in the same range as avoided detrimental effects to future people’s health thanks to CO2eq mitigation. Carbon footprint of EBRT is not neglectable and could be mitigated. When safely feasible, hypofractionation is one of the main factors to decrease this impact. Taking into account CO2eq emissions has a substantial impact on the health technology assessment of EBRT, favoring hypofractionated regimens.