Carbon Footprint of Patient and Staff Travel for Proton Therapy: How Many Trees do We Need to Offset It?

Abstract

<h3>Purpose/Objective(s)</h3> There is an increasing concern about rising carbon dioxide (CO2) levels and its hazardous impact on human health and climate change. Patients travel sometimes significant distances for their daily radiation treatments, especially for rare modalities such as proton therapy; the carbon footprint of this commute is not well understood. This study quantifies the distances traveled by patients and staff, and estimates their corresponding carbon footprint. Additionally, the study evaluates possible ways to offset CO2 equivalent emissions. <h3>Materials/Methods</h3> Patients treated between 07/2020 and 06/2021 at our proton program were evaluated. Their distance traveled was evaluated from their address using Google Maps. Most of the patients commuted daily, while some stayed for some nights at nearby hotels. Calculations assume full daily commute, as a worst-case scenario. Patients treated were reviewed for disease, site treated, and number of fractions. Staff members commute distances were evaluated and prorated depending on their proton therapy workload. EPA web calculator was used to convert distance in miles to kg of CO2, and the number of new trees required to offset it. <h3>Results</h3> There were 185 patients treated (average 19.9 per day); 63% had full course with protons, 31% had photon boost, and 6% had protons as boost. Total of 5,176 fractions were delivered (average 28 fractions per treatment course, maximum 42 fractions). The average patient distance traveled was 39 miles one way; 19 patients lived >100 miles away. An average patient course required 2,158 miles of commute. Total distance driven was 399,271 miles. Patients with prostate cancer accounted for highest average miles (3,517) per course; patients with CNS tumors accounted for the highest cumulative miles (100,207). The corresponding CO2 equivalent emissions were 859 kg per patient treatment course (range 15 kg to 5,147 kg); cumulative patient travel footprint was 158 metric tonnes of CO2 equivalent. To offset this footprint would require on average 14 new trees planted per patient (range 0.2 trees to 85 trees); total patient travel offset would require 2,625 new trees planted annually. There were 14 staff members supporting protons therapy. Their average daily commute was 31 miles, for total of 215 miles per day. This translated to 82,134 miles driven, 32 metric tonnes of CO2 equivalent, and 540 new trees planted annually. Per patient course treated, the incremental contribution was additional 177 kg of CO2 and 2.9 additional trees. <h3>Conclusion</h3> Travel carbon footprint of patients undergoing proton therapy was 859 kg CO2 per treatment course, which would require planting 14 new trees to offset. Staff travel contributed further 177 kg CO2 and additional 3 trees to be planted per patient. Strategies to lower CO2 footprint may include hypofractionation and optimizing transportation options, and we hope other radiation oncology practices will consider patient travel in evaluating their carbon footprint.