V. Kamenopoulou

Evaluation of neutron dose in the maze of medical electron accelerators.

MCNP code was used to simulate neutron and prompt gamma ray transport for a range of maze geometrical parameters, wall composition, and wall surface lining. Verification measurements were performed at two medical electron accelerator facilities. A very good agreement was observed between the results of the measurements and the MCNP simulation. MCNP code results were compared with the results of analytical equations used for the calculation of maze effectiveness, derived by Kersey and McCall. A good agreement exists between the simulation results and the results of the analytical methods for maze lengths longer than 8.5 m. However, the results of the present study showed that for shorter maze lengths, Kerseys method tended to overestimate neutron dose at the door entrance, whereas McCalls method with the neutron room scattered correction applied, showed an underestimation of neutron dose. Furthermore, according to MCNP simulation results, the use of barytes concrete instead of standard concrete as room shielding material, reduced neutron dose at the door entrance by about 20%. Finally, it was shown that lining with layers of wood and borated polyethylene significantly reduced the neutron dose at the door entrance by 45% and 65%, respectively.

An MCNP-based model for the evaluation of the photoneutron dose in high energy medical electron accelerators.

The development of a computational model for the treatment head of a medical electron accelerator (Elekta/Philips SL-18) by the Monte Carlo code mcnp-4C2 is discussed. The model includes the major components of the accelerator head and a pmma phantom representing the patient body. Calculations were performed for a 14 MeV electron beam impinging on the accelerator target and a 10 cmx10 cm beam area at the isocentre. The model was used in order to predict the neutron ambient dose equivalent at the isocentre level and moreover the neutron absorbed dose distribution within the phantom. Calculations were validated against experimental measurements performed by gold foil activation detectors. The results of this study indicated that the equivalent dose at tissues or organs adjacent to the treatment field due to photoneutrons could be up to 10% of the total peripheral dose, for the specific accelerator characteristics examined. Therefore, photoneutrons should be taken into account when accurate dose calculations are required to sensitive tissues that are adjacent to the therapeutic X-ray beam. The method described can be extended to other accelerators and collimation configurations as well, upon specification of treatment head component dimensions, composition and nominal accelerating potential.

Pre- and post-irradiation fading effect for LiF:Mg,Ti and LiF:Mg,Cu,P materials used in routine monitoring.

LiF is a well-known thermoluminescent (TL) material used in individual monitoring, and its fading characteristics have been studied for years. In the present study, the fading characteristics (for a period of 150 d) of various commercial LiF materials with different dopants have been evaluated. The materials used in the study are those used in routine procedures by the Personal Dosimetry Department of Greek Atomic Energy Commission and in particular, LiF:Mg,Ti (MTS-N, TL Poland), LiF:Mg,Cu,P (MCP-N, TL Poland), LiF:Mg,Cu,P (MCP-Ns, thin active layer detector, TL Poland) and LiF:Mg,Cu,P (TLD100H, Harshaw). The study showed that there is a sensitivity loss in signal of up to 20 % for the MTS-N material for a 150-d period in the pre-irradiation fading phase. The MCP-N has a stable behaviour in the pre-irradiation fading phase, but this also depends on the readout system. As far as the post-irradiation fading effect is concerned, a decrease of up to 20 % for the MTS-N material is observed for the same time period. On the other hand, the LiF:Mg,Cu,P material presents a stable behaviour within ± 5 %. These results show that the fading effect is different for each material and should be taken into account when estimating doses from dosemeters that are in use for >2 months.

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.

Prevention of and response to inadvertent exposure of embryo/fetus to ionizing radiation, due to medical exposure of the mother. The Greek regulatory authority initiatives

Embryo/fetus (E/F) irradiation as a result of medical exposure of the mother should be avoided, unless there are strong clinical indications. Medical practitioners are assigned the primary task and obligation of ensuring overall patient protection and safety in the prescription of and during the delivery of medical exposure. In cases of unintended exposure of embryo/fetus (E/F), the risk analysis and communication is conducted by or under the supervision of medical physicists at local level. National competent authorities can contribute to the prevention, risk analysis and communication of inadvertent E/F exposure to ionizing radiation by recording, analyzing and disseminating the relevant information. Since 2001, Greek Atomic Energy Commission has established a committee with the mandate to provide advice, to keep records, to analyze and disseminate the experience gained in cases of unintended E/F exposure. During the period 2001-2011, the committee was consulted by 269 pregnant women undergone medical exposures. The conclusions from the relevant data analysis, as well as the experience gained are herein presented and discussed.

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.

Decommissioning a phosphoric acid production plant: a radiological protection case study

During a preliminary survey at the area of an abandoned fertilizer plant, increased levels of radioactivity were measured at places, buildings, constructions and materials. The extent of the contamination was determined and the affected areas were characterized as controlled areas. After the quantitative and qualitative determination of the contaminated materials, the decontamination was planned and performed step by step: the contaminated materials were categorized according to their physical characteristics (scrap metals, plastic pipes, scales and residues, building materials, etc) and according to their level of radioactivity. Depending on the material type, different decontamination and disposal options were proposed; the most appropriate technique was chosen taking into account apart from technical issues, the legal framework, radiation protection issues, the opinion of the local authorities involved as well as the owners wish. After taking away the biggest amount of the contaminated materials, an iterative process consisting of surveys and decontamination actions was performed in order to remove the residual traces of contamination from the area. During the final survey, no residual surface contamination was detected; some sparsely distributed low level contaminated materials deeply immersed into the soil were found and removed.

Nuclear security and radiological preparedness for the olympic games, athens 2004: lessons learned for organizing major public events.

In light of the exceptional circumstances that arose from hosting the Olympic Games in Athens in 2004 and from recent terrorist events internationally, Greece attributes the highest priority to security issues. According to its statutory role, the Greek Atomic Energy Commission is responsible for emergency preparedness and response in case of nuclear and radiological events, and advises the Government on the measures and interventions necessary to protect the public. In this context, the Commission participated in the Nuclear, Radiological, Biological, and Chemical Threat National Emergency Plan, specially developed for the Olympic Games, and coordinated by the Olympic Games Security Division. The objective of this paper is to share the experience gained during the organization of the Olympic Games and to present the nuclear security program implemented prior to, during, and beyond the Games, in order to prevent, detect, assess, and respond to the threat of nuclear terrorism. This program adopted a multi-area coverage of nuclear security, including physical protection of nuclear and radiological facilities, prevention of smuggling of radioactive materials through borders, prevention of dispersion of these materials into the Olympic venues, enhancement of emergency preparedness and response to radiological events, upgrading of the technical infrastructure, establishment of new procedures for assessing the threat and responding to radiological incidents, and training personnel belonging to several organizations involved in the National Emergency Response Plan. Finally, the close cooperation of Greek Authorities with the International Atomic Energy Agency and the U.S. Department of Energy, under the coordination of the Greek Atomic Energy Commission, is also discussed.

EDUCATIONAL AND TRAINING ACTIVITIES IN PERSONAL DOSIMETRY IN GREECE

An individual monitoring programme is one of the main components of any radiation protection programme since it constitutes the mean for assessing and thus optimising the doses of occupationally exposed workers. The Greek Atomic Energy Commission (GAEC) is the competent authority for radiation protection and nuclear safety in Greece. GAECs educational and training activities in the field of occupational radiation protection at the national and regional (Eastern Europe) level are presented, along with the relevant activities of the University of Ioannina in the region of North-West Greece, as an example of a local education and training programme. The curricula of two postgraduate courses addressed to qualified experts and medical physics experts and mainly the modules dedicated to individual monitoring are discussed as well.