C.J. Hourdakis

The use of active personal dosemeters as a personal monitoring device: comparison with TL dosimetry

The use of active personal dosemeters (APDs) not only as a warning device but also, in some cases, as an official and hence stand-alone dosemeter is rapidly increasing. A comparison in terms of dose, energy and angle dependence, among different types of APD and a routinely used whole-body thermoluminescence dosemeter (TLD) has been performed. Significant differences were found between the TLD readings and mainly some not commonly used APDs. The importance of choosing the best adapted APD according to the radiation field characteristics is pointed out.

Establishment of diagnostic reference levels for dental intraoral radiography.

Diagnostic reference levels (DRLs) is a tool for the optimisation of radiological procedures. Establishment of a DRL is a requirement of national regulations. Measurements performed by the Greek Atomic Energy Commission on 529 dental intraoral radiographic facilities have been used in order to define DRLs for digital and film imaging modalities, taking into account the region of the mouth to be imaged. Thus, different DRL values have been proposed for minimum (usually incisors), maximum (usually maxillary molars) and average exposure settings, both for film and digital imaging. The results have been compared with similar studies performed in Europe and the USA and are in line with the most recent ones.

Comparison of full field digital (FFD) and computed radiography (CR) mammography systems in Greece

The purpose of this study is to evaluate and compare the performance of 52 full field digital (FFD) and computed radiography (CR) mammography systems checked by the Greek Atomic Energy Commission with respect to dose and image quality. Entrance surface air kerma (ESAK) was measured and average glandular dose (AGD) was calculated according to the European protocol on dosimetry in mammography. The exposures were performed using the clinical protocol of each laboratory. The image quality was assessed by the total score of resolved phantom structures incorporated in an American College of Radiology accreditation phantom. The mean ESAK values for FFD and CR systems were 4.59 ± 1.93 and 5.0 ± 1.78 mGy, respectively, whereas the AGD yielded a mean value of 1.06 ± 0.36 mGy for the FFD and 1.04 ± 0.35 mGy for the CR systems. Considering image quality, FFD systems indicated a mean total score of 13.04 ± 0.89, whereas CR systems a mean total score of 11.54 ± 1.06.

A National Survey: II. Performance of Medical Fluoroscopic X-Ray Systems in Greece

The results from a survey in 297 (46 % of the total) fluoroscopie X ray facilities in the private sector in Greece are presented. Certain fluoroscopic parameters for under-table tube and remote control over-table tube fluoroscopic systems have been evaluated, according to a specific quality control protocol and compared with acceptance limits. The results show that the overall performance of the fluoroscopic systems is below optimal, since only 55.5% of the fluoroscopic systems performed satisfactorily and in compliance with the radiation protection regulations. Remote control over-table tube fluoroscopic systems had much better performance characteristics than under-table tube systems, with respect to patient dose and image quality. A system of routine servicing as well as implementation of quality control on a regular basis are believed substantially to reduce variation fron the normal performance and system malfunctioning.

Image quality and patient dose in computed tomography examinations in Greece

The purpose of this study is to evaluate image quality of various computed tomography (CT) scanners installed in Greece, as well as to investigate patient doses from common CT examinations. An image quality survey was performed in 44 CT scanners countrywide. The imaging performance of the systems was evaluated by measurements of certain parameters, such as image noise, spatial uniformity, high- and low-contrast resolution and slice thickness accuracy. Moreover, preliminary results of patient dose survey are presented. Concerning image quality, 80 % of the scanners were found to be in compliance with the national legislation and relative international guidelines for all the examined parameters. Weighted CT dose index and dose-length product values for chest and abdomen routine examinations were generally below the dose reference levels (DRLs) suggested by the European Commission. However, some scanners were found to deliver significantly higher doses than the suggested DRL for head routine examinations. Finally, differences in the performance among scanners of the same type and similar age were observed, pointing out the importance of frequent calibration, routine quality control and proper maintenance.

A pilot study on the quality control of film processing in medical radiology laboratories in Greece

The results of a pilot study on the quality of film processing in 80 medical diagnostic radiology laboratories all over Greece are presented. The sensitometric technique for the evaluation of processing has been used to calculate films base + fog, maximum optical density, speed and contrast, parameters which describe the performance characteristics of automatic film processors and films. The mean values of the base + fog and the maximum optical density were well within the acceptance limits. The film speed was almost constant while the film contrast showed significant variation.

On the use of a novel Ferrous Xylenol-orange gelatin dosimeter for HDR brachytherapy commissioning and quality assurance testing

PURPOSE To evaluate a commercially available Ferrous-Xylenol Orange-Gel (FXG) dosimeter (TrueView™) coupled with Optical-Computed Tomography (OCT) read out, for 3D dose verification in an Ir-192 superficial brachytherapy application. METHODS Two identical polyethylene containers filled with gel from the same batch were used. One was irradiated with an 18 MeV electron field to examine the dose-response linearity and obtain a calibration curve. A flap surface applicator was attached to the other to simulate treatment of a skin lesion. The dose distribution in the experimental set up was calculated with the TG-43 and the model based dose calculation (MBCA) algorithms of a commercial treatment planning system (TPS), as well as Monte Carlo (MC) simulation using the MCNP code. Measured and calculated dose distributions were spatially registered and compared. RESULTS Apart from a region close to the containers neck, where gel measurements exhibited an over-response relative to MC calculations (probably due to stray light perturbation), an excellent agreement was observed between measurements and simulations. More than 97% of points within the 10% isodose line (80 cGy) met the gamma index criteria established from uncertainty analysis (5%/2 mm). The corresponding passing rates for the comparison of experiment to calculations using the TG-43 and MBDCA options of the TPS were 57% and 92%, respectively. CONCLUSION TrueView™ is suitable for the quality assurance of demanding radiotherapy applications. Experimental results of this work confirm the advantage of the studied MBDCA over TG-43, expected from the improved account of scatter radiation in the treatment geometry.

Establishment of diagnostic reference levels for dental panoramic radiography in Greece

The purpose of the present study was to present the national diagnostic reference levels (DRL) established for panoramic dental examinations in Greece. The establishment of DRL, as a tool for the optimisation of radiological procedures, is a requirement of national regulations. Measurements performed by the Greek Atomic Energy Commission on 90 panoramic systems have been used for the derivation of DRL values. DRL values have been proposed for exposure settings of different patient types (child, small adult and standard adult), both for film and digital imaging. The DRLs for different patient types are grouped in three categories: children, small adults (corresponding to female) and average adults (corresponding to male). Proposed DRLs for these groups are 2.2, 3.3 and 4.1 mGy, respectively. In order to investigate the correlation of DRLs with the available imaging modalities (CR, DR and film), this parameter was taken into account. DR imaging DRL is the lowest at 3.5 mGy, CR imaging the highest at 4.2 mGy and film imaging at 3.7 mGy. In order to facilitate comparison with other studies, kerma-width product values were calculated from Ki, air and field size.

IAEA-SSDL bilateral comparisons for diagnostic level air kerma measurement standards

Comparisons of national standard of air kerma for conventional and mammographic diagnostic X-ray radiation qualities were conducted by the IAEA. Eleven secondary standards dosimetry laboratories provided calibration data for Exradin A3 and Radcal RC6M transfer ionization chambers circulated. Each comparison result expressed as the ratio of the participant and IAEA calibration coefficient were within the acceptance limit of ±2.5%. From the 67 results of 11 participants and 10 available beam qualities, the comparison result was within its standard uncertainty in 63 cases, and within the expanded (k = 2) uncertainty in four cases. Detailed calibration uncertainty budgets from participant laboratories are presented. The relative standard calibration uncertainty of each participant was in the range of 0.5-1.3%. These results indicate that the calibration related uncertainty component is reasonable low for a clinical measurement. In addition to the calibration coefficient, other corrections should be applied for clinical measurement to achieve the recommended accuracy.