Estimating the Patient-specific Dose to the Thyroid and Breasts and Overall Risk in Chest CT When Using Organ-based Tube Current Modulation

Abstract

Purpose To assess the potential dose reduction to the thyroid and breasts in chest computed tomography (CT) with organ-based tube current modulation (OBTCM). Materials and Methods In this retrospective study (from January 2015 to December 2016), the location of the breasts with respect to the reduced tube current zone was determined. With Monte Carlo simulations, patient-specific dose distributions of chest CT scans were calculated for 50 female patients (mean age, 53.7 years ± 17.5; range, 20-80 years). The potential dose reduction with OBTCM was assessed. In addition, simulations of clinical OBTCM scans were made for 17 of the 50 female patients (mean age, 43.8 years ± 17.1; range, 20-69 years). Posterior organs in the field of view were analyzed and lifetime attributable risk (LAR) of cancer incidence and mortality was estimated. Image quality between standard CT and OBTCM scans was compared. Results No women had all breast tissue within the reduced tube current zone. Dose reductions of 18% in the thyroid and 9% in the breasts were observed, whereas the doses in lung, liver, and kidney were 17%, 11%, and 26% higher. Overall, the LAR for cancer incidence was not significantly different between conventional and OBTCM scanning (P = .06). Image quality improved with OBTCM (P < .002). Conclusion The potential benefit of OBTCM to the female breast in chest CT is overestimated because of a limited reduced tube current zone; despite a 9% dose reduction to the female breast, posterior organs will absorb up to 26% more radiation, resulting in no reduction in radiation-induced malignancies. RSNA, 2018.

Influence of risk-organ–based tube current modulation on CT-induced DNA double-strand breaks in a biological phantom model

“…Finally Wang et al found a dose reduction of 34–39% for the risk organ–based tube current modulation using a semianthropomorphic phantom [ 21 ]. Our results are in line with those studies, but there has been a recent study by Franck et al that showed there is only a 9% dose reduction in the female breast, in contrast to our results [ 22 ]. This difference can be explained in that, in their study, not all breast tissue was within the reduced tube current zone, and therefore the effect was not as big as if the breast tissue was within the reduced tube current zone.…”

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

“…Although this approach has been documented to reduce dose to superficial radiosensitive organs, it provokes a dose increase to centrally and posteriorly located organs. Franck et al [6] have shown that OTCM in thorax CT of females reduces the dose to thyroid and breast by 18% and 19%, respectively. However, the doses for lung, liver, and kidney were found 17%, 11%, and 26% higher.…”

“…However, this approach has been documented to deliver images of increased noise [10,11]. Previous studies performed in adult patients have shown that OTCM may substantially reduce radiation dose to superficial radiosensitive organs [6,8,12,13]. To our knowledge, there is scarce published data on the effect of OTCM on radiation dose to superficial radiosensitive organs and image quality in pediatric CT examinations [14,15].…”

“…Different CT vendors have adopted different approaches to implement OTCM. In one approach, implemented by Siemens Healthcare with X-CARE, mA is reduced when the x-ray tube rotates over the anterior quadrant of the body circumference, while it is increased over the lateral and posterior quadrants to preserve image quality [ 6 – 9 ]. However, an increase in dose absorbed by posterior located radiosensitive organs has been demonstrated [ 6 – 8 ].…”

Image quality and clinical usefulness of automatic tube current modulation technology in female chest computed tomography screening

“…A number of studies evaluated the influence of medical radiation exposure on future occurrence of malignant tumors in women who were exposed to high radiation doses due to multiple radiation examinations or treatment by radiotherapy. [ 14 – 16 ] However, the advantages of lung CT examination in revealing small pulmonary lesions has gradually become an important tool in physical examinations. In the conventional chest CT scanning procedure, the direct exposure of the breast to radiation is not avoidable, and the breast is not the target organ in lung CT screening; therefore, it is self-evident that the biological effect of frequent examinations or large doses of radiation might be a potential cancer risk.…”