Heart dose and coronary artery calcification in patients receiving thoracic irradiation for lung cancer

Background: Thoracic irradiation (TIR) is associated with an increased risk of coronary artery disease (CAD) and coronary-related death. Lung cancer patients receive considerable doses of TIR, making them a high-risk population that may benefit from post-therapy surveillance. Coronary artery calcium (CAC) is a known biomarker of CAD development and may serve as a useful indicator of disease progression in this population. We hypothesized greater CAC progression in lung cancer patients subjected to higher whole heart radiation doses. Methods: CAC progression (pre- and >2 years post-TIR) from chest CT scans of lung cancer patients were evaluated. A 2:1 matched control population was established controlling for age, gender, race, and CT scan interval. Vessel-specific CAC presence, progression, and extension in pre- and post-interval CT studies was evaluated by two blinded reviewers using the ordinal method. Dosimetric treatment files were restored and contours of the whole heart and proximal left anterior descending artery (LAD) were created within existing plans to compute radiation doses (Pinnacle Treatment Planning Software). Binary logistic regression analysis identified factors predictive for CAC development. Multiple logistic regression analysis with hierarchal method was used to assess covariates. Results: Thirty-five patients and 65 controls (50% female) were evaluated; mean age 57 years, mean follow-up post-radiation 4.9±2.2 years. Average mean and maximum left anterior descending coronary artery (LAD) radiation doses were 19.9 Gy (95% CI, 14.1-25.7) and 30.7 Gy (95% CI, 23.8-37.5), respectively; 91.6% inter-observer variability. There was greater incidence of coronary calcification in irradiated patients (48.6% vs. 24.6%; P=0.01). In interval CT scans, a greater proportion of radiated patients demonstrated new coronary calcification (P=0.007) and extension within the LAD (P=0.003). Radiation exposure was the only independent predictor of new calcification (OR 3.1; 95% CI: 1.09-9.2). Conclusions: We identified both an increase in the development and progression of CAC in lung cancer patients receiving TIR. Future studies utilizing alternative cancer populations and larger sample sizes are necessary to further correlate radiographic and dosimetric observations to cardiovascular events.