Estimating Carbon Dioxide Emissions and Direct Power Consumption of Linear Accelerator-Based External Beam Radiation...

Climate change is one of the direst health threats that humanity faces. We aim to estimate the carbon dioxide (CO₂) emissions associated with the energy usage from linear accelerator (LINAC)-based external beam radiation therapy (EBRT) for the most common cancer diagnoses.

We identified patients with the 4 most common cancer types treated with curative-intent EBRT. Beam-on time for each fraction was extracted from the treatment planning system and averaged over each site and treatment modality. The power was multiplied by the beam-on time in hours to yield kilowatt hours (kWh). Using the US Environmental Protection Agency Greenhouse Gas Equivalencies calculator, we converted the kWh into estimates of CO₂-equivalent emissions for the average US power grid. Idle time of the LINAC was estimated via Varian Medical Systems.

A total of 10 patients were included for each of the following modalities: conventionally fractionated for prostate cancer (28 fractions [fx]), prostate stereotactic body radiation therapy (SBRT) (5 fx), 15- and 5-fx regimens for early-stage breast cancer, 3- and 5-fx SBRT regimens for early-stage lung cancer, conventional EBRT (30 fx) for locally advanced lung cancer, and short- (5 fx) and long-course (25-28 fx) for rectal cancer. The modality with the lowest and highest carbon emissions per course, on average, was prostate SBRT (2.18 kg CO₂; interquartile range, 1.92-2.30) and conventional treatment for prostate cancer (17.34 kg CO₂; interquartile range, 10.26-23.79), respectively. This corresponds to CO₂-equivalent emissions of driving an average of 5.4 miles and 41.2 miles in a standard vehicle, respectively. "Standby" mode for a LINAC TrueBeam and Clinac IX uses 112 kWh and 64.8 kWh per day, respectively.

We have estimated CO₂ emissions arising from direct energy usage of a LINAC for 4 common cancers treated with EBRT. "Standby" mode of a LINAC uses the most energy per day. Comprehensive studies are warranted to minimize the environmental effects of health and cancer care.