Do Low-KVp CT Scans Increase the Dose Received by Superficial Organs?

Purpose:Tube voltages below 120 kVp are increasingly used in clinical CT. There are concerns that dose to superficial organs such as skin, thyroid, and breasts may be elevated at a low-kVp setting. Our purpose was to investigate the effect of low-kVp imaging on the dose received by deep-seated and superficial organs as well as the effective dose.Methods:Three computational patient models were included. They represented normal-weight, overweight, and obese adult females (BMI: 20–42). A Monte Carlo program developed and validated for a 128-slice CT system (Definition Flash, Siemens Healthcare) was used to simulate organ dose for chest and abdomen-pelvis scans at 70, 80, 100, 120, 140 kVps. Organ dose was subsequently used to calculate effective dose.Results:In chest CT, when CTDIvol was held constant, thyroid, breast, lung, and esophagus doses reduced with reducing kVp and were 22%, 5%, 9%, and 20% lower at 70 than 120 kVp for the normal-weight patient. The dose reduction percentages were even greater in general for the overweight and obese patients. Similar reduction in liver, colon, bladder, and ovary doses was found in abdomen-pelvis CT. Whole body averaged skin dose was nearly independent of kVp. In contrast, peak skin dose (over a 2 × 2 cm2 area) increased with reducing kVp and was 8–10% higher at 70 than 120 kVp. Regardless of patient size and exam type, when DLP was kept constant, effective dose reduced with reducing kVp and was 12–27% lower at 70 than 120 kVp.Conclusion:In adult body CT, using a low kVp setting to reduce CTDIvol corresponds to an even greater reduction in effective dose as well as the average dose received by deep-seated and most superficial organs. Provided that the low-kVp setting reduces CTDIvol by u003e10%, there will be no elevation of peak skin dose.