Determination of size specific conversion factors to effective dose using tld dosimeters in anthropomorphic phantoms

Introduction This study refers to effective dose (ED) estimation using the size-specific dose estimator (SSDE). Purpose This work aims at determining DLP SSDE -to-ED (k SSDE ) conversion factors where DLP SSDE is the length product multiplied by the appropriate f-factor (AAPM report 204) for chest-abdomen-pelvis (CAP) CT examinations in three weight-adjusted scan protocols and to compare the ED SSDE derived from k SSDE to that derived from k factors available in the literature. Materials and methods Three anthropomorphic phantoms of 55 kg, 73.5 kg and 96.2 kg body weight filled with 190 TLDs were scanned on a 64-slice multi-detector CT employing the respective weight-adjusted CAP-CT protocol used in clinical routine. Effective diameter was measured in the abdomen area of the phantoms and DLP SSDE was estimated using the respective f factor. For ED estimation, ICRP 103 tissue weighting factors for all organs inside and outside the irradiation field were used. Relevant k SSDE conversion factors were then calculated. These factors were then applied to 140 patients underwent CAP-CT examinations and the derived ED SSDE values were compared to corresponding ED k values. Results In the SSDE was 15.4% higher than ED k while in the medium category (60–90 kg) the corresponding percentage was 28.3%. For the over-weighted category (>90 kg) no significant difference in ED was observed. Conclusion Weight-adjusted DLP SSDE -to-ED conversion factors were determined. In low and medium weight categories, radiation dose may be underestimated when the patient size is not taken into consideration.