Personnel dose in diagnostic radiology is often underestimated. Typically the effective dose E is estimated based on dosimeters worn underneath the protective clothing measuring the personal dose equivalent Hp(10). This one-spot-measurement systematically neglects the exposure to the unshielded organs in the head and neck region. In this paper, energy dependent double dosimetry algorithms in the range of 30-80 keV are derived using organ dose conversion coefficients. The doses of shielded organs are assigned to a single dosimeter in the anterior thoracic region (chest) underneath the apron (Hp,c,u), and the doses of the organs not shielded are assigned to another dosimeter placed on the front area of the neck over the protective garment (Hp,n,o) with E = a1 Hp,c,u(10) + a2 Hp,n,o(10). Organs not completely shielded are categorized correspondingly. The coefficients a1 and a2 increase with higher energies up to 70 keV. The factors a2 are clearly higher according to ICRP 103 (rather than ICRP 60) because ICRP 103 considers additional organs in the head and neck region. According to ICRP 103, a conservative general algorithm with thyroid protection is E = 0.84 Hp,c,u(10) + 0.051 Hp,n,o(10) and without thyroid protection E = 0.79 Hp,c,u(10) + 0.100 Hp,n,o(10).

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.

Optimization of radiation protection devices for the operator is achieved by minimizing the effective dose (E) on the basis of the recommendations of Publications 60 and 103 of the International Commission on Radiological Protection (ICRP). Radiation exposure dosimetry was performed with thermoluminescence dosimeters using one Alderson phantom in the patient position and a second one in the typical position of the operator. Various types of protective clothing as well as fixed leaded shieldings (table mounted shielding and overhead suspended shields) were considered calculating E. Shielding factors for protective equipment can readily be misinterpreted referring to the reduction of the effective dose because fixed protective barriers as well as radiation protection clothing are shielding only parts of the body. With the ICRP 103 approach relative to the exposure without lead protection, a lead apron of 0.35 or 0.5 mm thickness reduces E to 14.4 or 12.3%, respectively; by using an additional thyroid collar, these values are reduced to 9.7 or 7.5%. A thyroid collar reduces the effective dose by more than an increase of the lead equivalency of the existing apron. Wearing an apron of 0.5 mm lead-equivalent with a thyroid collar and using an additional side shield, E decreases to 6.8%. Using both a fixed side and face shield decreases E to 2.0%. For protective garments including thyroid protection, the values of the effective dose in cardiac catheterization are 47-106% higher with ICRP 103 than with ICRP 60 recommendations. This is essentially caused by the introduction of new factors for organs in the head and neck region in ICRP 103.

In many standard situations in radiation protection the effective dose is underestimated if it is based on the depth personal dose equivalent Hp(10) measured with a single dosimeter in the anterior thoracic region (chest) underneath the protective apron (Hp,c,u). The estimate can be significantly improved by inclusion of a second dosimeter worn on the front area of the neck over of the protective garment (Hp,n,o) representing organs and areas that are usually not completely covered by the protective garment. The recent recommendations of the International Commission on Radiological Protection (ICRP) emphasize the contribution of the head and neck region to the effective dose. This accentuates the need for a valid representation of this body region in the effective dose algorithm. In this paper we derived coefficients for the two-dosimeter situation using phantom measurements for selected radiological procedures with different geometries between patient and investigator. According to ICRP 60, the algorithm with {without} thyroid protection is E = 0.64{0.64} Hp,c,u + 0.016{0.073} Hp,n,o. According to ICRP 103, the algorithm becomes E = 0.60{0.60} Hp,c,u + 0.047{0.094} Hp,n,o. The ICRP 103 model reveals that the underestimation of the effective dose based on Hp(10) using a single dosimeter worn under the protective garment is even higher than previously assumed based on ICRP 60. Future personal dosimetry should be qualified by a two-dosimeter concept. The head and neck region which is not covered by a conventional protective garment needs to be protected by mounted shielding or other constructive measures.

The use of thyroid protection collars is an effective preventive measure against exceeding occupational organ dose limits, and a thyroid shield also considerably reduces the effective dose. Therefore, thyroid protection collars should be a required component of anti-X protection.