Turan Olgar

Patient doses and dosimetric evaluations in interventional cardiology

Interventional cardiological examinations may be associated with excessive radiation exposures which may cause skin injuries and higher probabilities of stochastic effects. Dose-area product (DAP) and skin doses of 325 patients were measured using alternative dosimetric techniques for different cardiological examinations. Data were collected from five different systems with the involvement of 11 cardiologists. All these dosimetric information has been collected separately for each of 10 projections together with the exposure parameters of X-ray systems. Mean DAP values measured with a transparent ion chamber were 49.1 Gy cm(2), 66.8 Gy cm(2), 106.9 Gy cm(2) and 124.7 Gy cm(2), respectively, for coronary angiography (CA), percutaneous transluminal coronary angioplasty (PTCA) or stent (PT-SI), coronary angiography and/or PTCA and/or stent (CA-PT-SI), and ablation examinations. Radiochromic films, thermoluminescent dosimeters (TLD) and point measurement of air kerma (AK) were carried out for skin dose assessments. Skin doses of 23 patients measured with radiochromic films were found to be between 2 Gy and 6 Gy. Although the complexity of the procedures was the major reason for these excessive doses, considerable contributions of high X-ray output of some fluoroscopy units were also noticed. In addition to the direct measurement of DAP, alternative DAP values were also determined from the skin dose measurement techniques; exposed areas were summed on digitized radiochromic films in one technique, The product of AK reading with X-ray field size measured at the patient entrance using slow X-ray films was taken as another DAP. Good correlations were found among the DAP results and also between the entrance skin doses calculated from AK measurements and direct DAP readings (R(2)=0.91). A trigger DAP value of 130 Gy cm(2) for the 2 Gy of skin doses was derived from this relationship. Collection of dosimetric data for each projection was also investigated regarding a possible standardization of clinical techniques; in the case of coronary angiography examinations LAO 45 and RAO 30 were found as the dominant projections which may also simplify the dosimetric technique.

Radiation doses of patients and urologists during percutaneous nephrolithotomy

Renal stones can be treated either by extracorporeal shock wave lithotripsy (ESWL) or percutaneous nephrolithotomy (PCNL). Increasing use of fluoroscopic exposure for access and to detect stone location during PCNL make the measurement of patient and staff doses important. The main objective of this work was to assess patient and urologist doses for the PCNL examination. We used the tube output technique for determination of patient doses (n = 20) and lithium fluoride thermoluminescent dosimeter (TLD) chips for urologist dose measurements. The TLD technique was also used for some patient dose measurements (n = 7) for comparison with the tube output technique. Mean entrance skin doses of 191 and 117 mGy were measured by the tube output technique for anterior-posterior (AP) and right anterior oblique (RAO) 30 degrees /left anterior oblique (LAO) 30 degrees projections, respectively. The mean urologist doses for eye, finger and collar were measured as 26, 33.5 and 48 microGy per procedure, respectively. The mean effective dose per procedure for the urologist was 12.7 microSv. None of the individual skin dose results approach deterministic levels.

Patient and staff doses for some complex x-ray examinations

The aim of this study was to measure patient and staff doses simultaneously for some complex x-ray examinations. Measurements of dose-area product (DAP) and entrance skin dose (ESD) were carried out in a sample of 107 adult patients who underwent different x-ray examinations such as double contrast barium enema (DCBE), single contrast barium enema (SCBE), barium swallow, endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC), and various orthopaedic surgical procedures. Dose measurements were made separately for each projection, and DAP, thermoluminescent dosimetry (TLD), film dosimetry and tube output measurement techniques were used. Staff doses were measured simultaneously with patient doses for these examinations, with the exception of barium procedures. The measured mean DAP values were found to be 8.33, 90.24, 79.96 Gy cm(2) for barium swallow, SCBE and DCBE procedures with the fluoroscopy times of 3.1, 4.43 and 5.86 min, respectively. The calculated mean DAP was 26.33 Gy cm(2) for diagnostic and 89.76 Gy cm(2) therapeutic ERCP examinations with the average fluoroscopy times of 1.9 and 5.06 min respectively. Similarly, the calculated mean DAP was 97.53 Gy cm(2) with a corresponding fluoroscopy time of 6.1 min for PTC studies. The calculated mean entrance skin dose (ESD) was 172 mGy for the orthopaedic surgical studies. Maximum skin doses were measured as 324, 891, 1218, 750, 819 and 1397 mGy for barium swallow, SCBE, DCBE, ERCP, PTC and orthopaedic surgical procedures, respectively. The high number of radiographs taken during barium enema examinations, and the high x-ray outputs of the fluoroscopic units used in ERCP, were the main reasons for high doses, and some corrective actions were immediately taken.

Assessment of radiation doses to cardiologists during interventional examinations.

The accuracy of two on line dosimetric techniques was investigated for the estimation of cardiologist doses. The first technique involves the establishment of a database relating the cardiologist extremity doses to patient DAP values. Doses of nine cardiologists were measured together with patient doses during the interventional cardiac examinations of 166 patients for this purpose. Data were collected from five cardiology departments. The mean of the eye, thyroid, waist, right-left wrist, and right-left leg doses per procedure were measured as 72.4 (31.6-107.1), 68.5 (13.3-174.6), 11.2 (0.9-28.4), 67.8 (21.9-120.3) to 216 (52.7-425.4), and 137 (51.4-386.2) to 384 (135-1168.3) microGy/procedure. The effective doses were calculated according to the use of protection tools and a mean value of 12.14 (1.2-30.2) microSv/procedure was found. The ratios of staff dose to patient DAP were found to be within the range of 0.14-3.75 for each procedure. In the second method, cardiologist doses were calculated and compared with the measured values. Scatter doses were measured at the positions of cardiologists from Rando phantom exposures using similar conditions with patient procedures for this purpose. The parameters obtained from these exposures and patient examinations were used to calculate the doses to cardiologists.

Variations of Patient Doses in Interventional Examinations at Different Angiographic Units

PurposeWe analyzed doses for various angiographic procedures using different X-ray systems in order to assess dose variations.MethodsDose-area product (DAP), skin doses from thermoluminescent dosimeters and air kerma measurements of 308 patients (239 diagnostic and 69 interventional) were assessed for five different angiographic units. All fluoroscopic and radiographic exposure parameters were recorded online for single and multiprojection studies. Radiation outputs of each X-ray system were also measured for all the modes of exposure using standard protocols for such measurements.ResultsIn general, the complexity of the angiographic procedure was found to be the most important reason for high radiation doses. Skill of the radiologist, management of the exposure parameters and calibration of the system are the other factors to be considered. Lateral cerebral interventional studies carry the highest risk for deterministic effects on the lens of the eye. Effective doses were calculated from DAP measurements and maximum fatal cancer risk factors were found for carotid studies.ConclusionsInterventional radiologists should measure patient doses for their examinations. If there is a lack of necessary instrumentation for this purpose, then published dose reports should be used in order to predict the dose levels from some of the exposure parameters. Patient dose information should include not only the measured quantity but also the measured radiation output of the X-ray unit and exposure parameters used during radiographic and fluoroscopic exposures.

Radiation Exposure to Premature Infants in a Neonatal Intensive Care Unit in Turkey

Objective The aim of this work was to determine the radiation dose received by infants from radiographic exposure and the contribution from scatter radiation due to radiographic exposure of other infants in the same room. Materials and Methods We retrospectively evaluated the entrance skin doses (ESDs) and effective doses of 23 infants with a gestational age as low as 28 weeks. ESDs were determined from tube output measurements (ESDTO) (n = 23) and from the use of thermoluminescent dosimetry (ESDTLD) (n = 16). Scattered radiation was evaluated using a 5 cm Perspex phantom. Effective doses were estimated from ESDTO by Monte Carlo computed software and radiation risks were estimated from the effective dose. ESDTO and ESDTLD were correlated using linear regression analysis. Results The mean ESDTO for the chest and abdomen were 67 µGy and 65 µGy per procedure, respectively. The mean ESDTLD per radiograph was 70 µGy. The measured scattered radiation range at a 2 m distance from the neonatal intensive care unit (NICU) was (11-17 µGy) per radiograph. Mean effective doses were 16 and 27 µSv per procedure for the chest and abdomen, respectively. ESDTLD was well correlated with ESDTO obtained from the total chest and abdomen radiographs for each infant (R2 = 0.86). The radiation risks for childhood cancer estimated from the effective dose were 0.4 × 10-6 to 2 × 10-6 and 0.6 × 10-6 to 2.9 × 10-6 for chest and abdomen radiographs, respectively. Conclusion The results of our study show that neonates received acceptable doses from common radiological examinations. Although the contribution of scatter radiation to the neonatal dose is low, considering the sensitivity of the neonates to radiation, further protective action was performed by increasing the distance of the infants from each other.

Investigation of mean glandular dose versus compressed breast thickness relationship for mammography

The relationship between the mean glandular dose (MGD) and the compressed breast thickness (CBT) is commonly used for the presentation of mammographic dose survey results and could also be useful for the assessment of individual breast doses retrospectively in case of lack of necessary dosimetric instrumentation. The high data scattering from the best fit reduces the reliability of this technique. The aim of this study was to investigate the accuracy of this relationship using the data collected from a patient survey and phantom experiment. Patients were divided into three different groups according to their breast glandularities, which were predicted from the inspection of previous mammograms. X-ray beam qualities that will be used in patient examinations were determined according to breast thickness and predicted glandularities. The MGD versus CBT relationship for all the examined patients resulted in a poor correlation (R2 = 0.28). This relationship was separately obtained for each glandularity group and also for sub-groups of specific beam qualities. The best correlation (R(2) = 0.73) was obtained for the fatty breast group and Mo/Mo combination. A low correlation (R2 = 0.34) was observed in the mid-glandularity group due to inclusion of a wide range of glandularities in this group. In the case of the dense breast group, although the glandularity range was narrow, there were e still high data scattering (R2 = 0.25). This was probably due to the use of Mo/Rh and Mo/Mo combinations. This is validated by obtaining the MGD-CBT relationship specific to Mo/Mo combination (R2 = 0.61).

Performance measurements of mammographic systems

Performance measurements of 30 mammographic installations were carried out in order to see the current level of image quality and breast doses.The half of the systems tested in this survey indicated automatic exposure control and beam collimation problems. Film processing and dark room conditions were not optimum for the majority of the installations. Image quality phantoms were exposed by the user and team of the survey at each visited center. Lower breast doses were obtained at equal image qualities for the radiographs of the team indicating the importance of adequate handling of some exposure parameters. Corrective actions were suggested to each installation and necessary guidance was advised for the implementation of routine quality control activities.

Investigation of grid performance using simple image quality tests

Antiscatter grids improve the X-ray image contrast at a cost of patient radiation doses. The choice of appropriate grid or its removal requires a good knowledge of grid characteristics, especially for pediatric digital imaging. The aim of this work is to understand the relation between grid performance parameters and some numerical image quality metrics for digital radiological examinations. The grid parameters such as bucky factor (BF), selectivity (Σ), Contrast improvement factor (CIF), and signal-to-noise improvement factor (SIF) were determined following the measurements of primary, scatter, and total radiations with a digital fluoroscopic system for the thicknesses of 5, 10, 15, 20, and 25 cm polymethyl methacrylate blocks at the tube voltages of 70, 90, and 120 kVp. Image contrast for low- and high-contrast objects and high-contrast spatial resolution were measured with simple phantoms using the same scatter thicknesses and tube voltages. BF and SIF values were also calculated from the images obtained with and without grids. The correlation coefficients between BF values obtained using two approaches (grid parameters and image quality metrics) were in good agreement. Proposed approach provides a quick and practical way of estimating grid performance for different digital fluoroscopic examinations.

Investigation of noise sources for digital radiography systems

The performance of digital radiography systems can be evaluated in terms of spatial resolution and noise. Noise plays an important role in the achievable image quality for detecting small and low-contrast structures in digital images created by these systems. Our aim in this study was to investigate the noise sources both in the spatial and frequency domain for three digital radiography systems, one digital fluoroscopy system, and one digital mammography system, and to obtain information about the effective operating dose range of these detectors. Noise evaluation in the spatial domain was done with the relative standard deviation–detector air kerma relationship evaluation method. The characterization of the noise in the spatial domain gives information about the types of noise, but does not give information about the noise power distribution in frequency space. Therefore, noise evaluation in the frequency domain was carried out by noise power spectrum measurement. The observed dominant noise component at lower detector doses was electronic noise for the digital mammography system, whereas structured noise was observed to make up nearly half of the total noise at higher detector doses for one of the digital radiography systems. The structured noise component was increased by use of a grid in these systems, independent of the grid ratio and grid frequency, but this increase was lower for higher grid frequencies. Furthermore, the structured noise coefficient was decreased with gain and offset calibrations. The five systems which we evaluated behaved as a quantum noise limited for clinically used detector doses.