The correlation of effective dose from calculation method and the patient skin dose measurement using solid state detector for abdominal computed tomography examination

Abstract

Computed Tomography (CT) is a diagnostic imaging modality resulting in higher patient dose than other radiological procedures. As the rapid growing of CT, the patient dose from CT examination is questioned and needed to know. As the direct measurement of patient dose is not practical, the patient skin dosemeter (PSD) has been developed by Unfors to measure dose directly. The aim of this study is to determine the patient dose from abdominal CT using PSD and correlate to the calculated methods. Fifty-eight patients in CT upper abdomen and eighty-six in CT whole abdomen were prospectively included in the study. The collected data were patient age, gender, height, weight, body thickness, kVp, effective mAs, slice thickness, number of series, CTDI[subscript vol] and DLP from CT scanner, Siemens SOMATOM Sensation 16 at King Chulalongkorn Memorial Hospital. The effective dose was determined by applying the conversion factor for different regions of the body and patient groups and scanner factor. In this study, the PSD was attached to the patient skin close to the gonad (over left ovary position for female and over left testis position for male) to measure the skin dose. Result: The average patient skin dose, CTDI[subscript vol], DLP and effective dose per scan series for CT upper abdomen were 0.27 ± 0.22 mGy, 11.77 ± 1.02 mGy, 352.26 ± 44.35 mGy•cm and 5.24 ± 0.69 mSv respectively. For CT whole abdomen, the results per scan series were 7.64 ± 3.56 mGy, 11.41 ± 0.94 mGy, 485.59 ± 66.80 mGy•cm and 7.02 ± 1.40 mSv, respectively. The diagnostic reference levels (DRLs) for CT abdomen is 35 mGy for CTDI[subscript w], 800 mGy.cm for DLP and 12.0 mSv for effective dose. The average patient skin dose, CTDI[subscript vol], DLP and effective dose for all series were 1.10 ± 1.01 mGy, 42.12 ± 10.18 mGy, 1260 ± 337.67 mGy•cm and 18.71 ± 5.02 mSv, respectively for upper abdomen and 31.50 ± 14.69 mGy, 42.26 ± 11.74 mGy, 1763.19 ± 410.74 mGy•cm and 25.46 ± 6.63 mSv for whole abdomen which were very high as the protocol for CT abdomen requires 3-5 series. Conclusions: The effective dose could be determined by using the correlation between the average effective dose and the skin dose of the value 17.82 mSv.mGy-1 and 0.92 mSv.mGy[superscript -1] for upper and whole abdomen, respectively.