2007 Recommendations of the ICRP Change Basis for Estimation of the Effective Dose: What is the Impact on Radiation Dose Assessment of Patient and Personnel?

Purpose In radiation protection regulations the algorithm for effective dose calculation is based on Publication 60 (1990) of the International Commission on Radiological Protection (ICRP). The modifications to the tissue weighting factors in Publication 103 (2007) of the ICRP will affect the present methodology of calculating the effective dose and will also have an impact on its assessment. This paper evaluates circumstances under which the application of the new model yields relevant dose differences compared to the prevailing model. Materials and methods Effective doses were calculated and compared from the measured organ doses according to ICRP 60 and ICRP 103, respectively. The measurements of patient doses were carried out with an anthropomorphic phantom for thoracic and coronary CT examinations. Exposure of radiological personnel was measured based on the geometry of angiographic examinations using two anthropomorphic phantoms. Results The change of the weighting factor for the breast from 0.05 to 0.12 leads to a noticeable increase in the effective dose for thoracic (21 %) and coronary (31 %) CT examinations. Calculating sex-specific effective doses based on ICRP 60, the dose for coronary CT examination for women is 1.7 times higher than for men. Based on ICRP 103, the difference between female and male doses increases to a factor of 3.3. Due to the consideration of organs in the head and neck region as introduced in ICRP 103, for angiography the personnel is exposed to 24 - 50 % and 38 - 142 % higher doses with and without thyroid protection, respectively. Thereby, the official personal dosimetry will underestimate the effective dose according to ICRP 103 by a factor of 1.6 - 2.4 with thyroid protection and 1.1 - 1.4 without thyroid protection. Conclusion The revision of the parameters for effective dose calculation leads to higher doses and greater sex-specific differences for radiological examinations involving exposure of the breast. This effect should be considered when justifying any radiological examination. For the personnel, the new model results in higher effective doses due to increased emphasis on the organs in the head and neck region. Hence to optimize radiation protection of personnel, the use of radiation-protective shielding for this region becomes more important.