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Health care contributes to the global climate crisis with a footprint representing 4.4% of global net emissions. Fuel consumption is at the heart of health care’s emissions. Hypofractionationated radiotherapy (HF RT) is an opportunity to reduce the impact of RT especially in breast cancer where non-inferiority of HF RT has been demonstrated. The primary aim of this project was to quantify the carbon footprint of our single-center 1 week breast RT workflow. Our secondary aim was to estimate the footprint benefit of ultra HF breast RT versus moderately HF or normofractionated (NF) RT.

A total of 120 patients treated with whole breast RT, without lymph node RT nor boost, at a total dose of 26 Gy in 5 fractions (fr) over 1 week from February 2021 to March 2022 were included. To estimate carbon emissions, the average beam on and off electricity consumption of a simulation CT scan GoSIM® Siemens and restricted IMRT at 5.2 Gy/fr on an Elekta VersaHD® linac with 6 MV photon beams including daily IGRT and computer consumption were estimated using values from manufacturers and a mean of 0.0569 kgeqCO2/kWh. Patients were asked their means of transport (by foot, public transports or car) and city from which they were commuting from day 1 (consultation, simulation CT and first fraction were all done on day 1) to day 5 to estimate travel emissions. We excluded 3 patients commuting by plane before and after RT as ultra HF RT was not offered close to their hometown. Patients commuting by car were assumed to travel by thermal car with a low fuel economy to provide a worst-case estimate with a mean fuel consumption of 0.218 kgeqCO2/km. Carbon footprint of plastic consumables for deep inspiration breath hold was included.

The mean travelling distance was 324 km (Standard Error (SE): 42 km) and the mean carbon footprint per patient for the whole 1 week breast RT was 67 kgeqCO2 (SE: 6.0). Pre and per treatment power consumption from RT heavy medical equipment and plastic consumables represented 7% and 1% of the total carbon footprint per patient respectively (Figure 1). Mean traveling distance was 64.8 km/day with a mean carbon footprint of 13.4 kgeqCO2/day. As travel was the main impacting factor, we could estimate that a reduction in the number of fractions from 25 (NF) or 15 (moderate HF) to 5 (ultra HF) for breast RT could reduce carbon footprint by a factor 5 or 3 respectively moving from 335 or 201 to 67 kg eq CO2.
If only 50% of breast cancer patients would be eligible for a 5 fractions RT in a country like France where NF RT is mostly used this would translate into a potential reduction of  7 906 000 kgeqCO2/year.

These results have demonstrated low environmental impact of the 1 week breast RT. Main environmental impact of RT is due to transportation. The environmental benefit together with the non- inferiority in efficacy and safety should be taken into account to favor implementation of ultra HF breast RT.