Female Breast, Lung, and Pelvic Organ Radiation from Dose-reduced 64-MDCT Thoracic Examination Protocols: A Phantom Study

Overall radiation dose from computed tomography (CT) scans has become a concern as the use of CT scans continues to grow and the risk of radiation-induced cancers continues to rise. This is especially true for CT pulmonary embolism (CT-PE) studies, which have been shown to be associated with an increased risk of breast cancer, and often are performed on younger patients or in patients who are pregnant. This study compared the phantom organ radiation dose to the breast, lungs, and pelvis from five CT-PE protocols using an anthropomorphic phantom model on a standard 64-detector CT scanner. The five protocols were chosen to represent current scanning practice patterns used to reduce overall radiation in CT-PE protocols with variation in scan length, section thickness, tube potential, pitch, tube current, noise index, and whether dose modulation was used. The outcomes measured included the total dose in milligrays to each organ as well as the volume CT dose index (vCTDI: the average dose delivered to the scan volume). When comparing the protocols used during the contrast injection phase of a CT-PE scan, protocol 3, which has been reported to decrease overall radiation dose to the breast in pregnant patients, did show a significant dose reduction when compared to protocol 4, which is used in non-pregnant patients (protocol 3 breast skin: 4.8 ± 1.8 mGy; 91.7% of vCTDI, vs. protocol 4 breast skin: 13.1 ± 5.5 mGy; 87.0% of vCTDI, p = 0.003). Overall dose to the breast parenchyma demonstrated a similar trend. Protocols used before contrast injection and in regular chest CT protocols demonstrated varying doses, with an experimental protocol delivering the lowest breast dose (breast skin: 1.9 ± 0.6 mGy, breast parenchyma 1.3 ± 0.4 mGy). In all five protocols, the lungs consistently received the highest overall radiation dose, and the dose to the pelvis was consistently low, never exceeding 0.2 mGy.