Reconstruction of organ doses for patients undergoing computed tomography examinations in Canada 1992-2019.

We derived the first comprehensive organ dose library for Canadian pediatric and adult patients who underwent computed tomography (CT) scans between 1992 and 2019 to support epidemiological analysis of radiation risk. We calculated organ absorbed doses for Canadian CT patients in two steps. First, we modeled Computed Tomography Dose Index (CTDI) values by patient age, scan body part, and scan year for the scan period between 1992 and 2019 using national survey data conducted in Canada and partially the United Kingdom survey data as surrogates. Second, we converted CTDI values to organ absorbed doses using a library of organ dose conversion coefficients built in an organ dose calculation program, the National Cancer Institute dosimetry system for CT. In result, we created a library of doses delivered to 33 organs and tissues by different patient ages and genders, scan body parts and scan years. In the scan period before 2000, the organs receiving the greatest dose in the head, chest and abdomen-pelvis scans were the active marrow (3.7-15.2 mGy), lungs (54.7-62.8 mGy) and colon (54.9-68.5 mGy), respectively. We observed organ doses reduced by 24% (pediatric head and torso scans, and adult head scans) and 55% (adult torso scans) after 2000. The organ dose library will be used to analyse the risk of radiation exposure from CT scans in the Canadian CT patient cohort.

Assessment of Cataract Risk after Diagnostic Head CT Scan Radiation Exposure in Ontario, Canada.

Ionizing radiation is one of the known risk factors for cataract development, however, there is still debate regarding the level of risk after low dose exposures. One of the largest sources of radiation exposure to the lens of the eye is diagnostic CT scans. The aim of this study was to examine whether ionizing radiation associated with head CT scans increases cataract risk in residents of Ontario, Canada. Data were collected from January 1, 1994 to December 31, 2015 (22 years) from anonymized Ontario Health Insurance Plan (OHIP) medical records for over 16 million subjects. A lens dose was estimated for each CT scan using the National Cancer Institute dosimetry system for CT (NCICT) program combined with Canada-specific CTDIvol data. Multivariate Cox proportional hazards analysis was performed with cataract extraction surgery as the primary outcome and lens dose as the main variable of interest, with inclusion of various medical and demographic covariates. Lag periods of 3, 5 and 7 years were incorporated. When lens dose was treated as a continuous variable, hazard ratios (per 100 mGy) ranged from 0.82 (0.80-0.84) to 1.10 (1.09-1.11) depending on the lag period. As a secondary analysis, when individuals were binned based on their total cumulative dose, no significant dose response pattern was observed in the low dose region. Overall, within the bounds of this study, the data do not support an increased risk of vision impairing cataracts after diagnostic head CT scan radiation exposure.

Cataract Formation and Low-Dose Radiation Exposure from Head Computed Tomography (CT) Scans in Ontario, Canada, 1994-2015.

Ionizing radiation exposure to the lens of the eye is a known cause of cataractogenesis. Administrative data from the Ontario Health Insurance Program was used to examine the association between low-dose radiation exposure from head CT scans and cataract extraction surgery for 16 million Ontarians over a 22-year period (1994-2015). Subjects were grouped based on the number of head CT scans they received, and a Cox proportional hazards analysis was used to determine if there was a correlation with cataract surgery. Covariates included in the analysis were age, sex, diabetes, hypertension and prior history of intraocular surgery. To account for the potentially long latency period between radiation exposure and cataract formation, the data were analyzed incorporating a 5- and 10-year lag between head CT scan exposure and cataract surgery. Both the 5- and 10-year lagged models followed a similar trend, where only the first three head CT scans significantly increased the risk of cataract surgery by 3-8%. Individuals receiving four or more head CT scans did not have an increased cataract risk and in several cases the risk was reduced. Overall, no positive dose-response relationship was seen between the number of head CT scans received and the risk of cataract surgery. Due to the nature of the data extracted from medical records, several uncertainties exist in the analysis related to dosimetry, ultraviolet light exposure and smoking status. Nonetheless, these results do not support an association between ionizing radiation from repeated head CT scans and cataract formation.

Use of emergency departments and primary care visits for asthma related conditions in the 3 years following an asthma education program.

BACKGROUND: This study examines changes in Primary Care Visits (PCVs) and Emergency Department Visits (EDVs) among 1918 patients with asthma who attended either two visits, one visit or were no-show referrals at the Dr. Patrick Gill Asthma Education Center (AEC) in Charlottetown Prince Edward Island (PEI) between January 1, 2003 and March 31, 2008 compared to 2799 controls selected from a list of PEI asthma patients developed for the Canadian Chronic Disease Surveillance System (CCDSS). METHODS: Hurdle regression was used to model counts of PCVs and negative binomial models were used to model counts of EDVs at 12 months prior to AEC contact and 0-1, >1 to 2 and >2 to 3 years after AEC contact. The PEI Research Board approved the project. RESULTS: No-show referrals had a significant increase in pediatric EDVs and PCVs in the first year after referral. The higher rates of PCVs and EDVs prior to contact with the AEC in patients referred to the AEC were reduced after contact with the AEC, although they remained significantly higher than the CCDSS controls. CONCLUSIONS: Compared to patients who attended the AEC, referred patients who did not attend the AEC did not achieve similar reductions in pediatric EDVs and PCVs in the first year after referral.

The effect of a smoking ban on hospitalization rates for cardiovascular and respiratory conditions in Prince Edward Island, Canada.

BACKGROUND: This is the first study to have examined the effect of smoking bans on hospitalizations in the Atlantic Canadian socio-economic, cultural and climatic context. On June 1, 2003 Prince Edward Island (PEI) enacted a province-wide smoking ban in public places and workplaces. Changes in hospital admission rates for cardiovascular (acute myocardial infarction, angina, and stroke) and respiratory (chronic obstructive pulmonary disease and asthma) conditions were examined before and after the smoking ban. METHODS: Crude annual and monthly admission rates for the above conditions were calculated from April 1, 1995 to December 31, 2008 in all PEI acute care hospitals. Autoregressive Integrated Moving Average time series models were used to test for changes in mean and trend of monthly admission rates for study conditions, control conditions and a control province after the comprehensive smoking ban. Age- and sex-based analyses were completed. RESULTS: The mean rate of acute myocardial infarctions was reduced by 5.92 cases per 100,000 person-months (P = 0.04) immediately after the smoking ban. The trend of monthly angina admissions in men was reduced by -0.44 cases per 100,000 person-months (P = 0.01) in the 67 months after the smoking ban. All other cardiovascular and respiratory admission changes were non-significant. CONCLUSIONS: A comprehensive smoking ban in PEI reduced the overall mean number of acute myocardial infarction admissions and the trend of angina hospital admissions.