RISK OF CANCER AND OCULAR DISEASES FOLLOWING CT SCANS

Abstract

Computed tomography (CT) is an essential tool in modern medicine, enabling quick and accurate diagnosis of various conditions. Since CT relies on ionizing radiation (IR) to produce internal images, its widespread use has led to concerns regarding patient safety, particularly in children who are more sensitive. In this thesis, the potential association between low-dose IR exposure from CT scans and the development of certain ocular conditions and cancers among residents of Ontario, Canada was studied. Data on CT scans were obtained from the Ontario Health Insurance Plan (OHIP) database. We first estimated organ doses from various CT procedures based on sex, age, and scan year, using CT dose index (CTDI) values from national surveys and dose coefficients from the National Cancer Institute dosimetry system for CT (NCICT). These dose estimates were then used to assess disease risk. All analyses were conducted using multivariate Cox regression, including demographic factors and relevant predisposing medical conditions as covariates. Appropriate lag periods were applied to account for disease latency. Using OHIP data from 1994 to 2023, we evaluated the risk of cataract and glaucoma in relation to radiation dose to the eye lens following head CT scans. Analyses based on cataract surgery, glaucoma diagnosis, or glaucoma treatment, lagged by 3, 5, and 7 years, showed no increased risk due to radiation exposure. Similarly, using data from 1992 to 2019, we studied the risk of leukemia, lymphoma, and brain tumors in individuals who had received CT scans at or before age 19. Analyses lagged by 2, 5, and 10 years revealed some elevated risks for the primary cancer types but also highlighted no association or even reduced risk for some known radiogenic cancer sub-types. Taken together, the results did not support a clear association between cancer risk and CT exposure in this population. Overall, this thesis provides valuable insight into the potential risks associated with CT scans, supporting clinicians in making more informed decisions when ordering these procedures.