Access to diagnostic imaging and incidental detection of differentiated thyroid cancer in Ontario: A population-based retrospective cohort study

Global increases in thyroid cancer incidence (>= 90% differentiated thyroid cancers; DTC) are hypothesized to be related to increased use of pre-diagnostic imaging. These procedures can detect DTC during imaging for con-ditions unrelated to the thyroid (incidental detection). The objectives were to evaluate incidental detection of DTC associated with standardized, regional imaging capacity and drivetime from patient residence to imaging facility (the exposures). We conducted a population-based retrospective cohort study of 32,097 DTC patients in Ontario, 2003-2017. We employed sex-specific spatial Bayesian hierarchical models to evaluate the exposures and examine the adjusted odds of incidental detection by administrative regions. Regional capacities of computed tomography and magnetic resonance imaging scanners are positively associated with incidental detection, but vary by sex. Contrary to hypothesis, drivetimes in urban areas are positively associated with incidental detection. Access to primary care may play a role in several administrative regions with higher adjusted odds of incidental detection.