TY - JOUR
AU - Petrović, Jelena, Stanković
AB - Abstract Medical personnel performing interventional procedures in cardiology and radiology is considered to be a professional group exposed to high doses of ionizing radiation. Reduction of the eye lens dose limit made its assessment in the interventional procedures one of the most challenging topics. The objective of this work is to assess eye lens doses based on the whole-body doses using methods of computational dosimetry. Assessment included different C-arm orientations (PA, LAO and RAO), tube voltages (80 –110 kV) and efficiency of different combinations of protective equipment used in interventional procedures. Center position at the height of the thyroid gives best estimate of eye lens dose, with spreads of 11% (13%), 13% (17%) and 14% (13%) for the left (right) eye lens. The conversion factors of 1.03 (0.83), 1.28 (1.06) and 1.36 (1.06) to convert whole body to eye lens dose were derived for positions of first operator, nurse and radiographer, respectively. The eye lens dose reduction factors for different combinations of applied protective equipment are 178, 5 and 6, respectively. INTRODUCTION A significant increase in X-ray utilization in interventional cardiology and radiology has been introduced recently. Increase is both in number of procedures performed worldwide as well as in complexity and duration of exposure time of a single procedure. The radiation doses to the staff involved in these procedures is significantly higher than the exposure of staff performing common diagnostic procedures(1–3). This fact requires specific attention in terms of occupational radiation protection in interventional cardiology (IC) and interventional radiology (IR). The eye lens is more sensitive to the ionizing radiation than previously considered. Numerous epidemiological studies conducted over the past decade have indicated that radiation injury to the eye can occur at dose levels far lower than the previously established threshold(4), especially in the case of chronic and prolonged exposure to small doses, which is the case with professional exposure in medicine(5–8). Until recently, the occurrence of cataract was considered a typical tissue reaction with a dose threshold of 5 Sv in the case of chronic exposure and 2 Sv in the case of acute exposures(4, 9). Bearing in mind, the latent period and the fact that cataract can occur at far lower doses than the previously established threshold the International Commission on Radiological Protection (ICRP) reduced the dose threshold for the effects of ionizing radiation on the eye lens to 0.5 Gy(4). A new dose threshold for tissue reactions also resulted in a reduction in the annual dose limit for eye lens from 150 mSv to 20 mSv(10). In the context of this new dose limitation,, there are evidences that the dose limit may be exceeded for certain groups of health professionals if appropriate personal and collective protective tools are not used or if the use of these devices is not adequate(11). Consequently, dosemetry for eye lens has become important research topics to the radiation protection scientific community. Numerous developments have been achieved related to the calibration procedures, dedicated eye lens dosemeters and eye lens monitoring procedures in order to implement them in workplace situations with sufficient level of practicality and accuracy(11–22). Medical staff performing interventional procedures typically wears a lead apron and one or two personal dosemeters(17). If double dosimetry is utilized, one whole-body dosemeter is worn above and another below the lead apron, in order to get the right estimation of effective dose. With lead apron shielding the torso area, extremities are more exposed to direct and scattered radiation and in some cases extremity dosemeters are also used for the staff member’s dose monitoring(21). Furthermore, for protection purposes, the staff in interventional procedures is asked to wear lead thyroid collar and to use ceiling suspended shield and/or lead glasses. Therefore, complex work environment requires a need for establishing a simple and practical eye lens monitoring procedure without increasing the number of dosemeters worn by the medical staff. Various options for eye lens dose assessment are available and their advantages and disadvantages being widely discussed throughout literature(16–18, 20). The objective of this work is to propose a simple method for eye lens dose assessment in interventional procedures, based on the conversion of the whole-body dose measured using a dosemeter worn above the apron to the eye lens dose for all professional groups, e.g. first operator, second operator/nurse and radiographer in the interventional room. In addition, the efficiency of the protective tools typically used in interventional procedures was evaluated. MATERIALS AND METHODS Monte Carlo Simulations Simulations required for this experiment were performed using Monte Carlo code MCNPX(23). Simulated geometry (Figure 1) consisted of X-ray source, phantoms for three operators and patient, tabletop and flat-panel detector, personal and collective protective equipment, and thermoluminescent dosemeters (TLD) from which conversion factors will be calculated. Figure 1. View largeDownload slide Geometry for Monte Carlo simulations. Figure 1. View largeDownload slide Geometry for Monte Carlo simulations. X-ray tube was modeled as a photon point source. Distance from source position to the flat-panel detector positioned above the source was 120 cm with tabletop placed in the middle of that distance. Source was directed using cone of beams and cone beam half-angle was calculated so that field of view would cover entire patient torso phantom. Positions of the source, center of the upper third of patient’s torso and center of the flat-panel detector were aligned with source positioned below tabletop. Spectrum for the X-ray source was obtained from the Spectrum processor described in IPEM Report 78(24) for tube voltages in range from 80 kV to 110 kV with incremented of 10 kV. All operators and patient bodies were modeled as a 180 × 40 × 20 cm3 phantom of muscle tissue which consisted of head, torso and legs sections. Protective lead apron 0.5-mm thick was modeled to cover operators from neck down to one-third of the legs. Protective glasses were modeled as 0.5-cm thick rectangular shape to cover the region of the eyes. This is considered as adequate approximation, since impact of shape of lead glasses has proven to be less important compared to the different tube projections/angulations(25). Ceiling suspended shield was modeled with rectangular plate of dimensions of 85 × 60 × 2 cm3 aimed to protect head and torso of the first operator. Material for protective glasses and ceiling suspended shield was lead glass. Simulated TLDs were divided into three sections: (1) five were positioned in front of the eyes (one is placed between eyes, two on the outside and two above the eyes), (2) three were positioned at the level of thyroid and (3) three at the chest level. TLDs were modeled as 5 × 4 × 1 cm3 block filled with 6LiF(26). All material components and densities are taken from literature(27). Simulations included three the most frequently used projections of the X-ray tube: posterior anterior (PA) in which the tube is directly beneath the patient and two anterior oblique projections, left (LAO) and right (RAO), in which the X-ray tube was rotated for +45 and −45 degrees. Following combinations of protective equipment (PE) were simulated: (1) both ceiling suspended protection screen and protective glasses are applied, (2) only ceiling suspended protection screen, (3) only protective glasses and (4) none of the protective equipment is used. To obtain the results of the simulations F6 tally for photons was used. F6 tally provides user with the energy deposition averaged over a cell in terms of MeV/g, which can easily be converted to be expressed in mSv. Number of simulated particles was 300 million which ensured that relative error was satisfactory low and that tallies passed all statistical tests. Validation of Monte Carlo Simulations To validate Monte Carlo simulations a set of measurements and simulations were performed. Measurements were performed in the interventional rooms of five different hospitals where interventional cardiology and radiology procedures are performed. Dose rates for three C-arm angulations and three operators’ positions (first operator—doctor, nurse and radiographer) were measured at the height of the eyes and the height of the chest using pressurized ionization chamber (Victoreen 451 P, Fluke Biomedical, USA) in terms of operational dosimetric quantity H*(10). The measured dose rates were converted to Hp(3), using ICRU conversional factors from air kerma to H*(10) and Hp(3) for N-80 standard beam quality(28–30). Monte Carlo simulations mimicking these measurements were performed in which ionization chamber was modeled as two concentric cylinders where the inner cylinder was filled with air and the outer cylinder was made out of aluminum. IU card was used when tallying so the results would be expressed as dose rate. Whole Body to Eye Lens Dose Conversion Dose for the left and right eye lens, for each operator’s position, is estimated by averaging the three tallies in cells which simulate TLDs positioned surrounding the eye. Then, the ratio between the eye lens dose and the dose measured by three tallies positioned on chest and three tallies positioned on thyroid was calculated. Finally, the average value of these ratios (averaged on the total number of simulations), and the spread to the mean ratio (coefficient of variance) were calculated considering all configurations. Lowest spread indicated the best position for whole-body dosemeter from which the eye lens doses will be estimated using calculated ratios. Efficiency of the Protective Tools Efficiency of radiation protection equipment used was calculated as a ratio of radiation dose to the lens of the eye when no protection equipment is used and when a certain combination of protective equipment is applied. RESULTS Results of the validation Monte Carlo calculation are presented in Figure 2, whereas the efficiency of the protective tools and conversion factor for the whole body to the eye lens dose are presented in Tables 1–4. Table 1. Efficiency of radiation protection tools for the position of first operator for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 3.2 3.8 52 1.6 133 8.2 RAOc 2.4 2.5 69 4.4 166 15 LAOd 3.9 4.8 3.4 1.1 16 7.6 90 PA 3.1 3.7 46 1.6 121 8.0 RAO 2.4 2.4 73 4.1 178 16 LAO 4.1 4.4 3.5 1.1 21 6.0 100 PA 3.1 3.4 49 1.7 140 7.5 RAO 2.4 2.6 51 3.8 94 15 LAO 3.7 5.3 3.8 1.1 13 6.9 110 PA 3.0 3.3 47 1.7 120 7.0 RAO 2.4 2.6 60 3.8 111 16 LAO 3.5 4.7 4.4 1.1 17 5.7 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 3.2 3.8 52 1.6 133 8.2 RAOc 2.4 2.5 69 4.4 166 15 LAOd 3.9 4.8 3.4 1.1 16 7.6 90 PA 3.1 3.7 46 1.6 121 8.0 RAO 2.4 2.4 73 4.1 178 16 LAO 4.1 4.4 3.5 1.1 21 6.0 100 PA 3.1 3.4 49 1.7 140 7.5 RAO 2.4 2.6 51 3.8 94 15 LAO 3.7 5.3 3.8 1.1 13 6.9 110 PA 3.0 3.3 47 1.7 120 7.0 RAO 2.4 2.6 60 3.8 111 16 LAO 3.5 4.7 4.4 1.1 17 5.7 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 1. Efficiency of radiation protection tools for the position of first operator for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 3.2 3.8 52 1.6 133 8.2 RAOc 2.4 2.5 69 4.4 166 15 LAOd 3.9 4.8 3.4 1.1 16 7.6 90 PA 3.1 3.7 46 1.6 121 8.0 RAO 2.4 2.4 73 4.1 178 16 LAO 4.1 4.4 3.5 1.1 21 6.0 100 PA 3.1 3.4 49 1.7 140 7.5 RAO 2.4 2.6 51 3.8 94 15 LAO 3.7 5.3 3.8 1.1 13 6.9 110 PA 3.0 3.3 47 1.7 120 7.0 RAO 2.4 2.6 60 3.8 111 16 LAO 3.5 4.7 4.4 1.1 17 5.7 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 3.2 3.8 52 1.6 133 8.2 RAOc 2.4 2.5 69 4.4 166 15 LAOd 3.9 4.8 3.4 1.1 16 7.6 90 PA 3.1 3.7 46 1.6 121 8.0 RAO 2.4 2.4 73 4.1 178 16 LAO 4.1 4.4 3.5 1.1 21 6.0 100 PA 3.1 3.4 49 1.7 140 7.5 RAO 2.4 2.6 51 3.8 94 15 LAO 3.7 5.3 3.8 1.1 13 6.9 110 PA 3.0 3.3 47 1.7 120 7.0 RAO 2.4 2.6 60 3.8 111 16 LAO 3.5 4.7 4.4 1.1 17 5.7 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 2. Efficiency of radiation protection tools for the position of second operator (nurse) for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.7 4.1 1.0 1.0 2.8 4.1 RAOc 1.9 2.4 1.1 1.1 2.4 2.7 LAOd 4.0 4.4 1.0 1.0 4.1 4.5 90 PA 2.6 3.5 1.0 1.0 2.7 3.5 RAO 1.9 2.4 1.1 1.0 2.3 2.6 LAO 3.5 4.4 1.0 1.0 3.6 4.6 100 PA 2.9 3.6 1.0 1.0 2.9 3.7 RAO 1.9 2.5 1.1 1.0 2.4 2.7 LAO 3.2 4.4 1.0 1.0 3.5 4.6 110 PA 2.7 3.7 1.0 1.0 2.8 3.7 RAO 2.0 2.5 1.1 1.0 2.4 2.7 LAO 3.3 4.6 1.0 1.0 3.4 4.9 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.7 4.1 1.0 1.0 2.8 4.1 RAOc 1.9 2.4 1.1 1.1 2.4 2.7 LAOd 4.0 4.4 1.0 1.0 4.1 4.5 90 PA 2.6 3.5 1.0 1.0 2.7 3.5 RAO 1.9 2.4 1.1 1.0 2.3 2.6 LAO 3.5 4.4 1.0 1.0 3.6 4.6 100 PA 2.9 3.6 1.0 1.0 2.9 3.7 RAO 1.9 2.5 1.1 1.0 2.4 2.7 LAO 3.2 4.4 1.0 1.0 3.5 4.6 110 PA 2.7 3.7 1.0 1.0 2.8 3.7 RAO 2.0 2.5 1.1 1.0 2.4 2.7 LAO 3.3 4.6 1.0 1.0 3.4 4.9 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 2. Efficiency of radiation protection tools for the position of second operator (nurse) for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.7 4.1 1.0 1.0 2.8 4.1 RAOc 1.9 2.4 1.1 1.1 2.4 2.7 LAOd 4.0 4.4 1.0 1.0 4.1 4.5 90 PA 2.6 3.5 1.0 1.0 2.7 3.5 RAO 1.9 2.4 1.1 1.0 2.3 2.6 LAO 3.5 4.4 1.0 1.0 3.6 4.6 100 PA 2.9 3.6 1.0 1.0 2.9 3.7 RAO 1.9 2.5 1.1 1.0 2.4 2.7 LAO 3.2 4.4 1.0 1.0 3.5 4.6 110 PA 2.7 3.7 1.0 1.0 2.8 3.7 RAO 2.0 2.5 1.1 1.0 2.4 2.7 LAO 3.3 4.6 1.0 1.0 3.4 4.9 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.7 4.1 1.0 1.0 2.8 4.1 RAOc 1.9 2.4 1.1 1.1 2.4 2.7 LAOd 4.0 4.4 1.0 1.0 4.1 4.5 90 PA 2.6 3.5 1.0 1.0 2.7 3.5 RAO 1.9 2.4 1.1 1.0 2.3 2.6 LAO 3.5 4.4 1.0 1.0 3.6 4.6 100 PA 2.9 3.6 1.0 1.0 2.9 3.7 RAO 1.9 2.5 1.1 1.0 2.4 2.7 LAO 3.2 4.4 1.0 1.0 3.5 4.6 110 PA 2.7 3.7 1.0 1.0 2.8 3.7 RAO 2.0 2.5 1.1 1.0 2.4 2.7 LAO 3.3 4.6 1.0 1.0 3.4 4.9 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 3. Efficiency of radiation protection tools for the position of third operator (radiographer) for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.1 3.8 1.0 1.0 2.1 3.9 RAOc 1.7 2.4 1.1 1.0 1.9 2.5 LAOd 2.7 5.6 1.0 1.0 2.7 5.6 90 PA 2.1 3.6 1.0 1.0 2.2 3.6 RAO 1.7 2.8 1.1 1.0 2.0 3.0 LAO 2.6 6.4 1.0 1.0 2.6 6.5 100 PA 2.2 3.9 1.0 1.0 2.3 3.9 RAO 1.6 2.1 1.1 1.0 1.8 2.1 LAO 2.9 4.3 1.0 1.0 2.9 4.3 110 PA 2.2 3.2 1.0 1.0 2.3 3.2 RAO 1.6 2.6 1.1 1.0 1.7 2.7 LAO 2.4 3.4 1.0 1.0 2.4 3.5 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.1 3.8 1.0 1.0 2.1 3.9 RAOc 1.7 2.4 1.1 1.0 1.9 2.5 LAOd 2.7 5.6 1.0 1.0 2.7 5.6 90 PA 2.1 3.6 1.0 1.0 2.2 3.6 RAO 1.7 2.8 1.1 1.0 2.0 3.0 LAO 2.6 6.4 1.0 1.0 2.6 6.5 100 PA 2.2 3.9 1.0 1.0 2.3 3.9 RAO 1.6 2.1 1.1 1.0 1.8 2.1 LAO 2.9 4.3 1.0 1.0 2.9 4.3 110 PA 2.2 3.2 1.0 1.0 2.3 3.2 RAO 1.6 2.6 1.1 1.0 1.7 2.7 LAO 2.4 3.4 1.0 1.0 2.4 3.5 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 3. Efficiency of radiation protection tools for the position of third operator (radiographer) for the left and right eye and different tube voltages and projections. Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.1 3.8 1.0 1.0 2.1 3.9 RAOc 1.7 2.4 1.1 1.0 1.9 2.5 LAOd 2.7 5.6 1.0 1.0 2.7 5.6 90 PA 2.1 3.6 1.0 1.0 2.2 3.6 RAO 1.7 2.8 1.1 1.0 2.0 3.0 LAO 2.6 6.4 1.0 1.0 2.6 6.5 100 PA 2.2 3.9 1.0 1.0 2.3 3.9 RAO 1.6 2.1 1.1 1.0 1.8 2.1 LAO 2.9 4.3 1.0 1.0 2.9 4.3 110 PA 2.2 3.2 1.0 1.0 2.3 3.2 RAO 1.6 2.6 1.1 1.0 1.7 2.7 LAO 2.4 3.4 1.0 1.0 2.4 3.5 Tube volt. (kV) Eye lens Left Right Left Right Left Right PEa Glasses Ceiling shield Both 80 PAb 2.1 3.8 1.0 1.0 2.1 3.9 RAOc 1.7 2.4 1.1 1.0 1.9 2.5 LAOd 2.7 5.6 1.0 1.0 2.7 5.6 90 PA 2.1 3.6 1.0 1.0 2.2 3.6 RAO 1.7 2.8 1.1 1.0 2.0 3.0 LAO 2.6 6.4 1.0 1.0 2.6 6.5 100 PA 2.2 3.9 1.0 1.0 2.3 3.9 RAO 1.6 2.1 1.1 1.0 1.8 2.1 LAO 2.9 4.3 1.0 1.0 2.9 4.3 110 PA 2.2 3.2 1.0 1.0 2.3 3.2 RAO 1.6 2.6 1.1 1.0 1.7 2.7 LAO 2.4 3.4 1.0 1.0 2.4 3.5 aPE, Protective equipment; Projection: bPA, Posterior anterior, cLAO/dRAO, Left/Right anterior oblique. Table 4. The conversion factor from whole-body dosemeter to the left and right eye lens doses for position of the first operator, nurse and radiographer for different projections and tube voltages. Operator position Tube voltage (kV) 80 90 100 110 Eye lens Left Right Left Right Left Right Left Right Projection Ratio (Spread) Ratio (Spread) Ratio (Spread) Ratio (Spread) First operator (Physician) Thyroid Left 0.95 (0.24) 0.82 (0.25) 0.88 (0.14) 0.57 (0.47) 0.87 (0.15) 0.75 (0.19) 0.89 (0.16) 0.76 (0.17) Thyroid Center 1.01 (0.14) 0.87 (0.17) 1.04 (0.14) 0.67 (0.46) 1.02 (0.11) 0.88 (0.13) 1.06 (0.12) 0.90 (0.13) Thyroid Right 1.30 (0.13) 1.11 (0.15) 1.27 (0.10) 0.84 (0.49) 1.24 (0.12) 1.07 (0.13) 1.28 (0.10) 1.09 (0.12) Center Left 0.98 (0.28) 0.84 (0.31) 0.98 (0.29) 0.62 (0.51) 0.99 (0.29) 0.85 (0.32) 0.99 (0.27) 0.84 (0.27) Center Chest 1.16 (0.25) 1.00 (0.28) 1.15 (0.25) 0.75 (0.54) 1.14 (0.25) 0.99 (0.27) 1.16 (0.24) 0.98 (0.25) Center Right 1.38 (0.28) 1.18 (0.29) 1.36 (0.24) 0.91 (0.58) 1.44 (0.22) 1.24 (0.24) 1.51 (0.23) 1.28 (0.24) Second operator (Nurse) Thyroid Left 1.10 (0.13) 0.95 (0.16) 1.06 (0.13) 0.89 (0.15) 1.15 (0.11) 0.91 (0.17) 1.19 (0.14) 0.98 (0.16) Thyroid Center 1.31 (0.24) 1.12 (0.20) 1.25 (0.16) 1.04 (0.13) 1.29 (0.17) 1.01 (0.16) 1.30 (0.13) 1.07 (0.10) Thyroid Right 1.50 (0.15) 1.28 (0.10) 1.55 (0.15) 1.30 (0.12) 1.58 (0.20) 1.23 (0.15) 1.51 (0.18) 1.23 (0.16) Center Left 1.28 (0.28) 1.11 (0.28) 1.37 (0.30) 1.15 (0.30) 1.44 (0.23) 1.13 (0.26) 1.47 (0.24) 1.21 (0.24) Center Chest 1.60 (0.22) 1.37 (0.20) 1.59 (0.32) 1.33 (0.30) 1.65 (0.32) 1.29 (0.31) 1.59 (0.29) 1.30 (0.27) Center Right 1.85 (0.26) 1.58 (0.23) 1.82 (0.22) 1.43 (0.26) 1.95 (0.26) 1.52 (0.24) 1.96 (0.30) 1.61 (0.29) Third operator (Radiographer) Thyroid Left 1.09 (0.14) 0.86 (0.12) 1.20 (0.17) 0.95 (0.14) 1.08 (0.19) 0.81 (0.14) 1.19 (0.19) 0.92 (0.22) Thyroid Center 1.39 (0.20) 1.08 (0.15) 1.42 (0.18) 1.12 (0.15) 1.29 (0.14) 0.97 (0.13) 1.36 (0.19) 1.05 (0.16) Thyroid Right 1.76 (0.22) 1.38 (0.20) 1.72 (0.23) 1.34 (0.16) 1.71 (0.28) 1.27 (0.20) 1.66 (0.17) 1.28 (0.16) Center Left 1.36 (0.22) 1.08 (0.25) 1.52 (0.17) 1.20 (0.15) 1.48 (0.32) 1.12 (0.31) 1.66 (0.35) 1.29 (0.36) Center Chest 1.80 (0.26) 1.41 (0.25) 1.75 (0.29) 1.37 (0.26) 1.75 (0.31) 1.31 (0.25) 1.90 (0.31) 1.47 (0.32) Center Right 1.96 (0.28) 1.54 (0.28) 2.30 (0.39) 1.81 (0.37) 2.23 (0.31) 1.67 (0.29) 2.03 (0.25) 1.57 (0.25) Operator position Tube voltage (kV) 80 90 100 110 Eye lens Left Right Left Right Left Right Left Right Projection Ratio (Spread) Ratio (Spread) Ratio (Spread) Ratio (Spread) First operator (Physician) Thyroid Left 0.95 (0.24) 0.82 (0.25) 0.88 (0.14) 0.57 (0.47) 0.87 (0.15) 0.75 (0.19) 0.89 (0.16) 0.76 (0.17) Thyroid Center 1.01 (0.14) 0.87 (0.17) 1.04 (0.14) 0.67 (0.46) 1.02 (0.11) 0.88 (0.13) 1.06 (0.12) 0.90 (0.13) Thyroid Right 1.30 (0.13) 1.11 (0.15) 1.27 (0.10) 0.84 (0.49) 1.24 (0.12) 1.07 (0.13) 1.28 (0.10) 1.09 (0.12) Center Left 0.98 (0.28) 0.84 (0.31) 0.98 (0.29) 0.62 (0.51) 0.99 (0.29) 0.85 (0.32) 0.99 (0.27) 0.84 (0.27) Center Chest 1.16 (0.25) 1.00 (0.28) 1.15 (0.25) 0.75 (0.54) 1.14 (0.25) 0.99 (0.27) 1.16 (0.24) 0.98 (0.25) Center Right 1.38 (0.28) 1.18 (0.29) 1.36 (0.24) 0.91 (0.58) 1.44 (0.22) 1.24 (0.24) 1.51 (0.23) 1.28 (0.24) Second operator (Nurse) Thyroid Left 1.10 (0.13) 0.95 (0.16) 1.06 (0.13) 0.89 (0.15) 1.15 (0.11) 0.91 (0.17) 1.19 (0.14) 0.98 (0.16) Thyroid Center 1.31 (0.24) 1.12 (0.20) 1.25 (0.16) 1.04 (0.13) 1.29 (0.17) 1.01 (0.16) 1.30 (0.13) 1.07 (0.10) Thyroid Right 1.50 (0.15) 1.28 (0.10) 1.55 (0.15) 1.30 (0.12) 1.58 (0.20) 1.23 (0.15) 1.51 (0.18) 1.23 (0.16) Center Left 1.28 (0.28) 1.11 (0.28) 1.37 (0.30) 1.15 (0.30) 1.44 (0.23) 1.13 (0.26) 1.47 (0.24) 1.21 (0.24) Center Chest 1.60 (0.22) 1.37 (0.20) 1.59 (0.32) 1.33 (0.30) 1.65 (0.32) 1.29 (0.31) 1.59 (0.29) 1.30 (0.27) Center Right 1.85 (0.26) 1.58 (0.23) 1.82 (0.22) 1.43 (0.26) 1.95 (0.26) 1.52 (0.24) 1.96 (0.30) 1.61 (0.29) Third operator (Radiographer) Thyroid Left 1.09 (0.14) 0.86 (0.12) 1.20 (0.17) 0.95 (0.14) 1.08 (0.19) 0.81 (0.14) 1.19 (0.19) 0.92 (0.22) Thyroid Center 1.39 (0.20) 1.08 (0.15) 1.42 (0.18) 1.12 (0.15) 1.29 (0.14) 0.97 (0.13) 1.36 (0.19) 1.05 (0.16) Thyroid Right 1.76 (0.22) 1.38 (0.20) 1.72 (0.23) 1.34 (0.16) 1.71 (0.28) 1.27 (0.20) 1.66 (0.17) 1.28 (0.16) Center Left 1.36 (0.22) 1.08 (0.25) 1.52 (0.17) 1.20 (0.15) 1.48 (0.32) 1.12 (0.31) 1.66 (0.35) 1.29 (0.36) Center Chest 1.80 (0.26) 1.41 (0.25) 1.75 (0.29) 1.37 (0.26) 1.75 (0.31) 1.31 (0.25) 1.90 (0.31) 1.47 (0.32) Center Right 1.96 (0.28) 1.54 (0.28) 2.30 (0.39) 1.81 (0.37) 2.23 (0.31) 1.67 (0.29) 2.03 (0.25) 1.57 (0.25) Table 4. The conversion factor from whole-body dosemeter to the left and right eye lens doses for position of the first operator, nurse and radiographer for different projections and tube voltages. Operator position Tube voltage (kV) 80 90 100 110 Eye lens Left Right Left Right Left Right Left Right Projection Ratio (Spread) Ratio (Spread) Ratio (Spread) Ratio (Spread) First operator (Physician) Thyroid Left 0.95 (0.24) 0.82 (0.25) 0.88 (0.14) 0.57 (0.47) 0.87 (0.15) 0.75 (0.19) 0.89 (0.16) 0.76 (0.17) Thyroid Center 1.01 (0.14) 0.87 (0.17) 1.04 (0.14) 0.67 (0.46) 1.02 (0.11) 0.88 (0.13) 1.06 (0.12) 0.90 (0.13) Thyroid Right 1.30 (0.13) 1.11 (0.15) 1.27 (0.10) 0.84 (0.49) 1.24 (0.12) 1.07 (0.13) 1.28 (0.10) 1.09 (0.12) Center Left 0.98 (0.28) 0.84 (0.31) 0.98 (0.29) 0.62 (0.51) 0.99 (0.29) 0.85 (0.32) 0.99 (0.27) 0.84 (0.27) Center Chest 1.16 (0.25) 1.00 (0.28) 1.15 (0.25) 0.75 (0.54) 1.14 (0.25) 0.99 (0.27) 1.16 (0.24) 0.98 (0.25) Center Right 1.38 (0.28) 1.18 (0.29) 1.36 (0.24) 0.91 (0.58) 1.44 (0.22) 1.24 (0.24) 1.51 (0.23) 1.28 (0.24) Second operator (Nurse) Thyroid Left 1.10 (0.13) 0.95 (0.16) 1.06 (0.13) 0.89 (0.15) 1.15 (0.11) 0.91 (0.17) 1.19 (0.14) 0.98 (0.16) Thyroid Center 1.31 (0.24) 1.12 (0.20) 1.25 (0.16) 1.04 (0.13) 1.29 (0.17) 1.01 (0.16) 1.30 (0.13) 1.07 (0.10) Thyroid Right 1.50 (0.15) 1.28 (0.10) 1.55 (0.15) 1.30 (0.12) 1.58 (0.20) 1.23 (0.15) 1.51 (0.18) 1.23 (0.16) Center Left 1.28 (0.28) 1.11 (0.28) 1.37 (0.30) 1.15 (0.30) 1.44 (0.23) 1.13 (0.26) 1.47 (0.24) 1.21 (0.24) Center Chest 1.60 (0.22) 1.37 (0.20) 1.59 (0.32) 1.33 (0.30) 1.65 (0.32) 1.29 (0.31) 1.59 (0.29) 1.30 (0.27) Center Right 1.85 (0.26) 1.58 (0.23) 1.82 (0.22) 1.43 (0.26) 1.95 (0.26) 1.52 (0.24) 1.96 (0.30) 1.61 (0.29) Third operator (Radiographer) Thyroid Left 1.09 (0.14) 0.86 (0.12) 1.20 (0.17) 0.95 (0.14) 1.08 (0.19) 0.81 (0.14) 1.19 (0.19) 0.92 (0.22) Thyroid Center 1.39 (0.20) 1.08 (0.15) 1.42 (0.18) 1.12 (0.15) 1.29 (0.14) 0.97 (0.13) 1.36 (0.19) 1.05 (0.16) Thyroid Right 1.76 (0.22) 1.38 (0.20) 1.72 (0.23) 1.34 (0.16) 1.71 (0.28) 1.27 (0.20) 1.66 (0.17) 1.28 (0.16) Center Left 1.36 (0.22) 1.08 (0.25) 1.52 (0.17) 1.20 (0.15) 1.48 (0.32) 1.12 (0.31) 1.66 (0.35) 1.29 (0.36) Center Chest 1.80 (0.26) 1.41 (0.25) 1.75 (0.29) 1.37 (0.26) 1.75 (0.31) 1.31 (0.25) 1.90 (0.31) 1.47 (0.32) Center Right 1.96 (0.28) 1.54 (0.28) 2.30 (0.39) 1.81 (0.37) 2.23 (0.31) 1.67 (0.29) 2.03 (0.25) 1.57 (0.25) Operator position Tube voltage (kV) 80 90 100 110 Eye lens Left Right Left Right Left Right Left Right Projection Ratio (Spread) Ratio (Spread) Ratio (Spread) Ratio (Spread) First operator (Physician) Thyroid Left 0.95 (0.24) 0.82 (0.25) 0.88 (0.14) 0.57 (0.47) 0.87 (0.15) 0.75 (0.19) 0.89 (0.16) 0.76 (0.17) Thyroid Center 1.01 (0.14) 0.87 (0.17) 1.04 (0.14) 0.67 (0.46) 1.02 (0.11) 0.88 (0.13) 1.06 (0.12) 0.90 (0.13) Thyroid Right 1.30 (0.13) 1.11 (0.15) 1.27 (0.10) 0.84 (0.49) 1.24 (0.12) 1.07 (0.13) 1.28 (0.10) 1.09 (0.12) Center Left 0.98 (0.28) 0.84 (0.31) 0.98 (0.29) 0.62 (0.51) 0.99 (0.29) 0.85 (0.32) 0.99 (0.27) 0.84 (0.27) Center Chest 1.16 (0.25) 1.00 (0.28) 1.15 (0.25) 0.75 (0.54) 1.14 (0.25) 0.99 (0.27) 1.16 (0.24) 0.98 (0.25) Center Right 1.38 (0.28) 1.18 (0.29) 1.36 (0.24) 0.91 (0.58) 1.44 (0.22) 1.24 (0.24) 1.51 (0.23) 1.28 (0.24) Second operator (Nurse) Thyroid Left 1.10 (0.13) 0.95 (0.16) 1.06 (0.13) 0.89 (0.15) 1.15 (0.11) 0.91 (0.17) 1.19 (0.14) 0.98 (0.16) Thyroid Center 1.31 (0.24) 1.12 (0.20) 1.25 (0.16) 1.04 (0.13) 1.29 (0.17) 1.01 (0.16) 1.30 (0.13) 1.07 (0.10) Thyroid Right 1.50 (0.15) 1.28 (0.10) 1.55 (0.15) 1.30 (0.12) 1.58 (0.20) 1.23 (0.15) 1.51 (0.18) 1.23 (0.16) Center Left 1.28 (0.28) 1.11 (0.28) 1.37 (0.30) 1.15 (0.30) 1.44 (0.23) 1.13 (0.26) 1.47 (0.24) 1.21 (0.24) Center Chest 1.60 (0.22) 1.37 (0.20) 1.59 (0.32) 1.33 (0.30) 1.65 (0.32) 1.29 (0.31) 1.59 (0.29) 1.30 (0.27) Center Right 1.85 (0.26) 1.58 (0.23) 1.82 (0.22) 1.43 (0.26) 1.95 (0.26) 1.52 (0.24) 1.96 (0.30) 1.61 (0.29) Third operator (Radiographer) Thyroid Left 1.09 (0.14) 0.86 (0.12) 1.20 (0.17) 0.95 (0.14) 1.08 (0.19) 0.81 (0.14) 1.19 (0.19) 0.92 (0.22) Thyroid Center 1.39 (0.20) 1.08 (0.15) 1.42 (0.18) 1.12 (0.15) 1.29 (0.14) 0.97 (0.13) 1.36 (0.19) 1.05 (0.16) Thyroid Right 1.76 (0.22) 1.38 (0.20) 1.72 (0.23) 1.34 (0.16) 1.71 (0.28) 1.27 (0.20) 1.66 (0.17) 1.28 (0.16) Center Left 1.36 (0.22) 1.08 (0.25) 1.52 (0.17) 1.20 (0.15) 1.48 (0.32) 1.12 (0.31) 1.66 (0.35) 1.29 (0.36) Center Chest 1.80 (0.26) 1.41 (0.25) 1.75 (0.29) 1.37 (0.26) 1.75 (0.31) 1.31 (0.25) 1.90 (0.31) 1.47 (0.32) Center Right 1.96 (0.28) 1.54 (0.28) 2.30 (0.39) 1.81 (0.37) 2.23 (0.31) 1.67 (0.29) 2.03 (0.25) 1.57 (0.25) Figure 2. View largeDownload slide Results of validation of Monte Carlo simulations by comparison with experimental measurements in term of head to torso dose ratio. Figure 2. View largeDownload slide Results of validation of Monte Carlo simulations by comparison with experimental measurements in term of head to torso dose ratio. Head to torso dose ratios based on measurements in terms of H*(10) using an ionizing chamber (IC) for three different operators’ positions are presented in Figure 2. These values are further compared to the corresponding ratios obtained by Monte Carlo simulations (denoted MC). Tables 1–3 present reduction factors for the left and right eye lens dose for three typical projections (PA, RAO and LAO) and three combinations of the protective equipment (glasses, ceiling shield and both) for positions of the first operator, nurse and radiographer, respectively. Ratios and spreads for conversion from the using a whole-body dose to the eye lens dose are given in Table 4 for all three staff categories. DISCUSSION The results presented in this work revealed a single dosemeter worn above the apron can be used as a simple and practical method for eye lens dose assessment in interventional procedures. A dedicated passive dosemeter, type tested and calibrated in terms of Hp(3) is the best approach for eye lens dose assessment. However, one must have in mind that contrary to the whole-body dosimetry, eye lens dosimetry is not currently well established in practice(31). In the cases when a specific dosemeter is not available, alternative options for eye lens dose assessment need to be considered. These include use of active dosemeters, correlations to patient dose indices, use of typical eye lens doses from literature or estimation through dosemeters calibrated in terms of Hp(10) and Hp(0.07) through proper correction factors(16, 18, 20, 22). Previous studies confirmed that the dose measurements using a whole-body dosemeters worn outside the lead apron (or dosemeters worn on thyroid collar) can be used to calculate the eye lens dose. This approach requires knowledge of conversion factors from whole body to eye lens dose for different setups and additional correction for the use of protective tools. Monte Carlo method provides a way to get an estimate of doses to the eye lens simulating the work environment of staff involved in interventional procedures(15, 32). Parameters that affect dose to the workers, beside the number of procedures and exposure time and number of series in a single procedure, are also the geometry, collimation, the position of the image receptor and X-ray tube. Therefore, the conversion from whole body to eye lens doses was derived all staff categories presented in the interventional room. These can be used to assess the eye lens doses by taking into account conditions that reflect a typical clinical environment during fluoroscopically guided interventional procedures in cardiology or radiology. As presented in Figure 2, the results of the validation of simulations showed good agreement between simulated results and measurements. The observed discrepancies are likely due to uncertainty of measurement and difference in static geometry used for Monte Carlo simulation and dynamic environment typical for clinical practice, also observed in the previous similar studies(33–35). Available literature data indicated that there are significant differences in the reduction factors due to the use of protective tools(22). This can be e explained by the simultaneous impact of multiple parameters affecting the dose to the lens of the eye, including the distance for the source of the scattered radiation, relative position of monitors and protective screen in the room, radiation field size, X-ray beam quality, the height of the operators and the complexity of the procedure(21). The method used for dose assessment (simulation, measurement with phantom or with patients) inevitably affects the results. Simulation and phantom measurements are related to the static, fixed conditions, whereas measurements on operators take into account factors related to the dynamic nature of the procedure, like change of the operator’s position in the room and improper position of protective screens. Depending on the assessment method used, dose reduction factors due to use of ceiling suspending screen can vary from factor 1.3 up to 33, whereas lead glasses contribute to dose reduction from a factor 5 to a factor 33(22). Evermore, the operator’s head orientation towards the radiation source (related to the position of the monitors in the X-ray room) and fit of the eyewear glasses to the face shape are identified as crucial parameters contribution to the eye glasses protective efficiency(15, 34). Due to multiple influencing factors, overall dose reduction achieved with combination of multiple protective tools can vary from a factor 25 to the factor of 143(22). This is in line with results presented in this work, as overall dose reduction for the combination of the lead glasses and ceiling protective screen for the first operator ranges from a factor 13 to 178. As presented in the Table 1, considering the left eye, dose reduction factor for ceiling suspended screen and protective glasses are in the range 3.4–73 and 2.4–4.8, respectively, which is again well in line with above mentioned published results. It is important to underline that the ceiling suspended screen is primarily effective for the first operator. Using only one protective screen leaves positions of the nurse and radiographer less protected, as indicated in the second columns of Tables 2 and 3. Reduction factor for ceiling suspended screen for nurse and radiographer is 1 (which means it provides no reduction of dose) and their eye lens doses are reduced only by the effect of lead glasses with reduction factors of 2–5 for nurse position and 2–6 for radiographer position, respectively. Employing an additional suspended ceiling shield positioned perpendicular to the position of the first operator significantly reduces the dose to the eye lenses of the second and third operator by the factor similar to those for the first operator, as shown in Table 1. As presented in Table 4, for the first operator, for both left and right eye lens two positions were indicated which will provide best estimate of the eye lens dose. For the left eye lens, thyroid center position has lowest spread for one out of four tube voltages and thyroid right has lowest spread for three out of four tube voltages. For thyroid center position, the spread is 11% while for the thyroid right position the spread is 10% for two tube voltages, giving this position advantage for eye lens dose estimate. For the right eye lens, results also indicate thyroid center (spread 13%) and thyroid right (spread 12%) as two possible positions for whole-body dosemeter which would give the reasonable estimate of the eye lens dose. For both eye lenses, thyroid right position is better than thyroid center position by only 1% which in terms of doses involved in interventional cardiology and radiology is negligible. Similar results can be observed for the nurse position. In this case, for the left eye lens dose best estimate is given by thyroid left position for three out of four tube voltages with the spread from 11% to 14% and 14% for remaining tube voltage for which thyroid center has spread of 13%. The right eye lens dose is best estimated positioning TL dosemeter at thyroid right position for three out of four tube voltages with the spread ranging from 10% to 15%, and thyroid center position for fourth tube voltage with spread of 10%. Results for the radiographer indicate that for the left eye lens each of thyroid center, thyroid left and chest left positions give the best estimate for one of the four simulated voltages with spreads 14%, 14% and 17%, respectively, and for fourth tube voltage thyroid left and chest left have equal lowest spread of 17%. For the right eye lens, thyroid left position gives best estimate for two tube voltages with spreads 12% and 14%, while thyroid center positions is best estimate for other two tube voltages with spreads of 13% and 16%. Since the goal of this work was to find optimal position for placing one whole-body dosemeter which would give best estimate for both eye lens doses. The overall results for the range of tube voltage typically used in interventional procedures revealed that whole-body dosemeter worn at the thyroid center position gives best estimate of the eye lens dose for all operating positions. Furthermore for first operator, the spread goes from 11% to 14% for left eye lens with average conversion coefficient of 1.03 and from 13% to 46%, with the average conversion coefficient was estimated to 0.83 for the right eye. For nurse, the spread goes from 13% to 24% for left eye lens with average conversion coefficient of 1.28 and from 10% to 20%, with the average conversion coefficient was estimated to 1.06 for the right eye. For radiographer, the spread goes from 14% to 20% for left eye lens with average conversion coefficient of 1.36 and from 13% to 16%, with the average conversion coefficient was estimated to 1.06 for the right eye. Previous studies confirmed that the vast majority (90%) of the interventional cardiologists from the wear the dosimeter on the chest(17, 18). Therefore, whole-body to eye lens dose conversion obtained either by Monte Carlo simulations or from clinical measurements are inevitably useful for eye lens dose assessment in IC (18, 25, 36). In addition to the practical aspects of the proposed methodology, this study improves the prospective assessment of cumulative eye lens doses, in particular for the more exposed eye, in the framework of radiation-induced risk assessment of lens opacities. Nevertheless, the main limitation of such approach is that there is no guarantee that the whole-body dosimeter will be used properly and systematically. Although the conversion factor from whole body to eye lens dose vary considerably (11–24% spread for the left eye and 13–46% for the right eye), the eye lens dose estimates remain of major interest for both prospective and retrospective dosimetry studies. It should be underlined that knowledge of the exact position of the whole-body dosemeter is a key prerequisite for reliable dose assessment, in particular in situations when this dosimeter can be partially shielded by the operators’ body(36). Other sources of uncertainty should also be considered as change of the relative position of the operator with respect to the patient, variation in properties and use of protective tools and variations in the procedure itself(17, 25, 36). Overall, the identified limitations of this study can be summarized as: the simulations are performed in well-known and static exposure conditions that could different form the clinical environments, the adequacy and regularity of use of personal protective tools vary in clinical practice and this cannot be taken into account here, the exact position on the whole-body dosimeter is not always known and the individual variations of operator’s working habits and level of procedure complexity cannot be taken into account. Nevertheless, the important advantage of this study is that conversion coefficient from the whole body to eye lens dose were performed by simulations that included use of different protective tools in the single numerical experiment setup, that it takes into account different angulations and change of the beam quality trough the procedure. Not less important, conversion coefficients for the whole body to the eye lens dose, in addition to the first operator, are provided for the nurse and for the radiographer. Finally, the presented results are in good agreement with previously published similar studies. The good agreement was demonstrated both in terms of influence of defined geometry used for Monte Carlo simulations in evaluating the efficiency or protective equipment(34, 35) and in terms of position and ratio of the dose from whole-body dosemeter and eye lens doses(25, 36, 37). CONCLUSION A computational algorithm for eye lens does assessment using whole-body dose values is presented in this work. Assessment included different X-ray beam projections as well as efficiency of different combinations of protective equipment used in interventional procedures. From the presented results, choosing the center position at the height of the thyroid would give overall best estimate for the eye lens dose with spreads of 11% (13%), 13% (17%) and 14% (13%) for the left (right) eye lens for positions of first operator, nurse and radiographer and corresponding conversion factors of 1.03 (0.83), 1.28 (1.06) and 1.36 (1.06), respectively. Reduction factor for different combinations of applied protective equipment are 13–178, 2–5 and 2–6 for first operator, nurse and radiographer. The ceiling shield seems not to be effective in reducing doses of nurse and radiographer. 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TI - OCCUPATIONAL EYE LENS DOSE ESTIMATED USING WHOLE-BODY DOSEMETER IN INTERVENTIONAL CARDIOLOGY AND RADIOLOGY: A MONTE CARLO STUDY
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncy283
DA - 2019-01-09
UR - https://www.deepdyve.com/lp/oxford-university-press/occupational-eye-lens-dose-estimated-using-whole-body-dosemeter-in-bSD65y9uoq
SP - 1
VL - Advance Article
IS - 
DP - DeepDyve
ER -