Wildfire smoke exposure and radiation oncology outcomes in rural Manitoba lung cancer patients: a systematic review

Abstract

Background: Climate change-driven wildfires are increasing in frequency and intensity. The 2025 Manitoba wildfire season, which burned over one million hectares, exposed rural and Indigenous lung cancer patients undergoing radiation therapy to unprecedented levels of fine particulate matter (PM_2.5) and triggered widespread evacuations, severely threatening treatment continuity and outcomes. This systematic review examines the evidence (2010–2023) on the impact of wildfire smoke exposure on radiation oncology outcomes in rural and Indigenous lung cancer patients, with particular attention to its applicability to the Manitoba context.

Methods: PRISMA-guided systematic review of PubMed, Scopus, and Web of Science (1 January 2010–31 July 2025). Studies were included if they addressed wildfire smoke or PM_2.5 exposure, lung cancer, radiation therapy outcomes, and rural or Indigenous populations. Quality was assessed using the Newcastle-Ottawa Scale for observational studies and CASP checklists for reviews/qualitative studies. Findings were narratively synthesized.

Results: Fifteen moderate-to-high-quality studies were included (four cohort, two qualitative, five reviews, two meta-analysis, one scoping review, one observational). Wildfire-derived PM_2.5 exacerbates radiation-induced lung toxicities (e.g., pneumonitis reported in up to 30% of thoracic radiotherapy patients) via oxidative stress and inflammation. High PM_2.5 exposure is linked to increased mortality/complications (adjusted OR 1.15, 95% CI 1.05–1.26) and respiratory hospitalizations (RR 1.12, 95% CI 1.07–1.18). Treatment interruptions exceeding 7 days-common during wildfire evacuations-reduce local control by ~10% and elevate mortality risk (HR 1.14, 95% CI 1.03–1.26). Rural and Indigenous patients experience disproportionate barriers, including limited healthcare access, long travel distances, socioeconomic constraints, and culturally insensitive services.

Discussion: Wildfire smoke significantly worsens radiation therapy outcomes in rural lung cancer patients through synergistic pulmonary toxicity and treatment disruptions. No Manitoba-specific studies were identified, highlighting a critical evidence gap. Urgent interventions are needed: mobile radiation units, subsidized high-efficiency air filtration, culturally safe care models, telehealth expansion, and province-specific research to address climate-related health inequities in radiation oncology.

Keywords

lung cancer / radiation therapy / wildfire smoke / PM2.5 / radiation pneumonitis / treatment interruptions / rural health / Indigenous health

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