Carbon Footprint of Photon Therapy

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Rising carbon dioxide levels have hazardous impact on human health and climate change. This study estimates the energy utilization of radiation therapy and estimates corresponding carbon footprint. Patients treated between 07/2020 and 06/2021 using a Varian LINAC system were evaluated. Power draw was directly measured in 1 second increments, from the LINAC machine and the radiation department facility. Patients treated were reviewed for number of fractions and beam duration during each fraction. kWh power consumption was calculated per fraction and per treatment course. Patient commute distance was evaluated using Google Maps. EPA calculator was used to calculate CO2 equivalent (CO2e) footprint. There were 176 patients treated for 191 treatment courses. Total of 4,517 fractions were delivered (avg 23.6, range 1 to 48). Average BeamOn time was 141 seconds per fraction (22 to 310 sec); electron plans (n = 8) 29 sec, 2D/3D (n = 63) 77 sec, and IMRT (n = 120) 182 sec. BeamOn power draw was ∼36.3 kW. Power consumption per fraction was 1.4 kWh (0.2 to 3.0 kWh), and per course 37.5 kWh (0.9 to 109.1 kWh). LINAC was otherwise in standby mode 71% of time (∼7.3 kW) and ON/ready mode 25% (∼12.5 kW). Patient BeamOn time accounted for 2% of total its time and 8% of its power use during the year. Incremental standby/ready energy contribution per treatment course was 410 kWh (78,332/191). The building power draw was 12.5 kW, for incremental contribution of 576 kWh per course. Average patient travel distance was 9.6 miles (0.7 miles to 73.5 miles), resulting in 711-mile round trip per course (6 miles to 5620 miles). Corresponding carbon footprint for BeamOn time was 0.6 kg CO2e per fraction (electrons 0.1 kg, 2D/3D 0.3 kg, and IMRT 1.1 kg per fx). The treatment course footprint was 16.2 kg CO2e (0.4 kg to 47.2 kg). The attributed standby/ready LINAC footprint was 177.8 kg CO2e per course. The attributed facility footprint was further 250.0 kg CO2e per course. The attributed commute footprint was further 286.3 kg CO23 per course (2.4 kg to 2264.0 kg). The entire treatment course was 730.4 kg CO2e. As such, single fraction was 0.1% of the total CO2e course (0.01% to 0.27%), BeamOn was 2.3% (0.1% to 7.1%), LINAC standby/ready was 28.0% (6.5% to 41.3%), building was 39.4% (9.2% to 58%), and commute was 30.3% (0.6% to 82.9%). The entire program generated 139.5 metric tons of CO2e during the year. Linear accelerator BeamOn carbon footprint varied as a function of technique but was only 2% of the overall patient treatment footprint. The LINAC standby electricity contributed 28%, building electricity 39%, and commute 30%, though this varied significantly per patient, as a function of number of fractions and treatment distance. Fixed CO2e contribution from the standby LINAC and the building draw accounted for ∼67% of the footprint. However, radiation oncologists can potentially impact the overall carbon footprint by prescribing fewer fractions to lower total commute, as clinically indicated.