Room: Exhibit Hall | Forum 9
Purpose: Typically, in an annual survey, skin exposure is not measured in CT. The goal of this project was to estimate the skin exposure from CTDI_100 from annual survey data.
Methods: Measurements were taken using a Radcal 10x5-6 6cc ion-chamber with a 16cm diameter CTDI phantom on a GE Lightspeed 64-Slice CT. Exposures were measured for 80, 100, 120, and 140kVp and 40, 120, and 200mm scan lengths at 200mA, 1s rotation time, and nT=40mm at â€œ12 oâ€™clockâ€? on the phantom. For the different scan lengths and kVp, the entrance kerma was compared to central CTDI_100 for the same protocol taken from annual data. Exposures were also measured at different positions on the phantom for fixed scan technique of 140kVp, 200mA, 1s, and 200mm scan length. Exposures were taken for 0Â° and 90Â° scout images at the 12, 3, and 9 oâ€™clock positions at 120kVp, 80mA, and 200mm scan length. These scout exposures were also compared to the skin exposures for the 120kVp CT acquisition at 200mm.
Results: For varying kVps at the fixed scan lengths, skin exposure varied from 1312mR to 4753mR for 40mm, 1578mR to 5694mR for 120mm, and 1607mR to 5779mR for 200mm. For the entrance kerma-to-CTDI_100 ratio, values ranged from 0.94 to 1.31. Exposures measured at different positions ranged from 5250mR to 5779mR. For the scouts, the exposures ranged from 121.3mR to 251.0mR, at 0Â°, and from 18.54mR to 254.6mR, at 90Â°, ranging from 0.44% to 6.02% of 120kVp CT exposure.
Conclusion: The results give an idea of the skin exposure at different points on the phantom for CT and scout acquisitions. Using these methods, it is possible to get an estimation of skin dose using materials provided. With this data, it is possible to estimate skin exposure from CTDI_100 measured during annual survey.