Evaluating Carbon Footprint of Proton Therapy Based on Power Consumption and Possible Mitigation Strategies

There is increasing concern about rising carbon dioxide (CO₂) emissions and their hazardous effect on human health. This study quantifies the energy utilization of proton therapy, assesses the corresponding carbon footprint, and discusses possible offsetting strategies toward carbon-neutral health care operations.

Patients treated between July 2020 and June 2021 using the Mevion proton system were evaluated. Current measurements were converted to kilowatts of power consumption. Patients were reviewed for disease, dose, number of fractions, and duration of beam. The Environmental Protection Agency calculator was used to convert power consumption to tons of CO₂ equivalent (CO₂e) for scope-based carbon footprint accounting.

There were 185 patients treated and a total of 5176 fractions delivered (average, 28). Power consumption was 55.8 kW in standby/night mode and 64.4 kW during BeamOn, for an annual total of 490 MWh. BeamOn time was 149.6 hours, and BeamOn consumption accounted for 2% of the machine total. Power consumption was 52 kWh per patient (breast, highest at 140 kWh; prostate, lowest at 28 kWh). Annual power consumption of the administrative areas was approximately 96 MWh, for a program total of 586 MWh. The carbon footprint for BeamOn time was 4.17 metric tons of CO₂e, or 23 kg per patient course (breast cancer, 60 kg; prostate, 12 kg). The annual carbon footprint for the machine was 212.2 tons CO₂e, and for the proton program, 253.7 tons CO₂e, with an attributed footprint of 1372 kg CO₂e per patient. The corresponding CO₂e offset for the program could be 4192 new trees planted and grown for 10 years (23 trees per patient).

The carbon footprint varied by disease treated. On average, the carbon footprint was 23 kg of CO₂e per patient and 253.7 tons of CO₂e for the proton program. There are a number of reduction, mitigation, and offset strategies possible for radiation oncologists that should be explored, such as waste minimization, less treatment commuting, efficient energy use, and renewable electricity power use.