The Impact of PM2.5 on Radiation-induced Pneumonitis in Patients With Breast Cancer

Background/Aim: Exposure to particulate matter (PM) air pollution is known to adversely affect respiratory disease, but no study has examined its effect on radiationinduced pneumonitis (RIP) in patients with breast cancer. Patients and Methods: We conducted a retrospective review of 2,736 patients with breast cancer who received postoperative radiation therapy (RT) between 2017 and 2020 in a single institution. The distance between the PM measurement station and our institution was only 3.43 km. PM data, including PM2.5 and PM10, were retrieved from the open dataset in the official government database. Results: Overall incidence rate of RIP was 1.74%. After adjusting for age, RT technique, regional irradiation, fractionation and boost, the average value of PM2.5 was significantly associated with a higher risk of RIP (p=0.047) when patients received >= 20 fractions of RT. Specifically, PM2.5 >= 35 (mu g/m3) showed a significantly higher risk of RIP (p=0.019) in patients with >= 20 fractions of RT. Conclusion: This is the first study to reveal the association between PM2.5 and RIP in patients with breast cancer who received 20 fractions or more of postoperative RT. We demonstrated that high PM2.5 levels around the RT institution were associated with RIP, suggesting that reducing PM air pollution may be a modifiable risk factor.