Climate-driven disasters such as wildfires are increasing in both severity and frequency, posing serious threats to healthcare infrastructure, continuity of care, and patient well-being. Individuals undergoing cancer treatment are particularly vulnerable, as care often requires frequent and time-sensitive visits over several weeks to specific treatment centers—especially in the case of radiotherapy. However, the impact of climate-related wildfires on radiotherapy treatment adherence remains largely unexplored.

This multi-institutional retrospective cohort analyzed 539,292 radiotherapy treatment appointments from eight clinics in Northern California between 2017–2021 and compared rates of missed visits during active wildfires. Wildfire data from the California Department of Forestry and Fire Protection (CAL FIRE) were used to correlate the proximity of wildfires (within a 50-kilometer [km] radius) to clinics. Missed visit rates were compared between treatment visits that coincided with active wildfires within 50-km and those that did not.

Overall, 8.8 % of appointments coincided with wildfires within a 50-km radius, and 4.9 % of these were missed. Wildfire exposure was associated with increased missed appointments (OR = 1.07, 95 % CI [1.02, 1.13], p = 0.007) after adjusting for seasonality, temporal trends, and clinic factors. Demographic analyses revealed no significant patient-specific disparities in missed treatments. The estimated financial impact of missed treatments was $2.14 million, highlighting economic vulnerabilities.

This initial investigation demonstrates a statistically significant trend towards higher non-adherence to radiotherapy visits during wildfires. This is the first multi-institutional study to investigate the impact of wildfires exposure on radiotherapy adherence and to quantify the associated financial impact. Our findings highlight the emerging intersection of climate change and cancer care delivery, emphasizing the need for health system resilience in the face of environmental threats.