In a Heartbeat: An Assessment of Dynamic Dose Variation to Cardiac Structures Using Dual Source Computed Tomography

Abstract

To assess radiation dose variation to the left anterior descending artery (LAD), left main coronary artery (LMCA), left ventricle (LV), and whole heart (WH) during the cardiac cycle using dual source computed tomography (DSCT). The present prospective study included patients with left-side breast cancer planned to undergo tangential radiation therapy. An electrocardiogram-synchronized contrast-injected DSCT scan was obtained with the patient in the treatment position, in deep-inspiration breath-hold, using retrospective sequential acquisition. The WH, LV, LMCA, and proximal, middle, and distal LAD segments were contoured on each phase of the cardiac cycle. The maximum, minimum, and mean Hausdorff distance between each structure and the tangential fields was assessed in ventricular systole and diastole. Four-dimensional dose-volume histograms were used to compare the systolic and diastolic dosimetric data. Ten patients were enrolled. The average maximum, minimum, and mean Hausdorff distance variation from systole to diastole was ≤4mm for the LV and LMCA and ≤3mm for the WH and LAD segments. WH maximum dose and volume receiving 5Gy were decreased in systole compared with diastole (42.9Gy versus 44.5Gy, P=.03, and 21.7cm3 versus 27.7cm3, P=.01), but the mean dose remained similar throughout the cycle. The maximum and mean dose to the distal LAD was 21.2Gy versus 26.6Gy(P=.005) and 8.6Gy versus 13.2Gy(P=.006) in systole versus diastole, respectively. The maximum and mean dose to the middle LAD was 18.4Gy versus 25.1Gy(P=.005) and 8.5Gy versus 10.2Gy in systole versus diastole (P=.005). The maximum dose to the LV was lower in systole than in diastole (21.5Gy vs 26.7Gy; P=.005). In addition to deep-inspiration breath-hold, systolic irradiation is associated with a reduction in dose to the LAD, LV, and WH. In addition to its potential use in radiation planning for cardiac gating, DSCT imaging can be used to help define a planning organ at risk volume for clinically important cardiac substructures.