TH-AB-207A-02: 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 >10%, there will be no elevation of peak skin dose.