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Aim/Introduction: Conventional preclinical internal dose estimates typically assume a uniform distribution of radioactivity and dose deposition throughout organ tissues. This assumption can deviate from reality for β-/α-emitting radioligands with a heterogeneous tissue activity distribution. In this study S-values for internal dosimetry of β- emitters were calculated for a multi-region model of a mouse kidney. The significance of regional S-values was demonstrated for the mouse kidney biodistribution of a 131I-labeled single-domain anti-HER2 antibody fragment with predominant uptake in the outer stripe of the outer medulla. Materials and Methods: A stylized computational model of a mouse kidney was developed, consisting on ellipsoids delimiting 5 tissue compartments: renal cortex, outer medulla outer/inner stripes (IS/OS), inner medulla and papilla. Energy absorbed fractions (ɸ) for the different kidney regions were calculated for 131I and 90Y, from photon-electron transport simulations using MCNP6.2 code. A sensitivity study on the influence of model specifications (kidney volume, cortex occupancy) was performed. For the 131I mouse study, time-dependent regional kidney-tissue activities were determined from the relative regional activity concentrations of kidney sections measured with digital β--particle autoradiography (using an iQID system), relative to the whole-kidney activity measured with conventional gamma counting. Results: For 131I, a large fraction of the emitted β- energy is absorbed within the sub-kidney source region itself (ɸ ≥0.60). Because of this and the smaller masses of sub-kidney tissues, the self-irradiation regional S-values are considerably higher (30% to >200% depending on kidney region) than whole-kidney S-values. Compared to 131I, 90Y regional self-absorbed fractions are lower (ɸ 0.10) between most regions for 90Y and between adjacent regions for 131I (e.g. cortex/OS, OS/IS). The sensitivity of self-absorbed fractions to the kidney model specifications was typically small for 131I (100% depending on region) from the uniform whole-kidney dose based on a homogeneous activity distribution. Conclusion: The calculated regional S-values, in combination with sub-kidney activity information, allow a more realistic estimation of the doses absorbed by different renal tissues from β--emitting radioligands with a heterogeneous kidney uptake. This provides new dose information relevant for preclinical investigations studying the risk of radiation-induced nephrotoxicity of these therapies.

Monte Carlo calculations were used to investigate the efficiency of radiation protection equipment in reducing eye and whole body doses during fluoroscopically guided interventional procedures. Eye lens doses were determined considering different models of eyewear with various shapes, sizes and lead thickness. The origin of scattered radiation reaching the eyes was also assessed to explain the variation in the protection efficiency of the different eyewear models with exposure conditions. The work also investigates the variation of eye and whole body doses with ceiling-suspended shields of various shapes and positioning. For all simulations, a broad spectrum of configurations typical for most interventional procedures was considered. Calculations showed that ‘wrap around’ glasses are the most efficient eyewear models reducing, on average, the dose by 74% and 21% for the left and right eyes respectively. The air gap between the glasses and the eyes was found to be the primary source of scattered radiation reaching the eyes. The ceiling-suspended screens were more efficient when positioned close to the patient’s skin and to the x-ray field. With the use of such shields, the H-p(10) values recorded at the collar, chest and waist level and the H-p(3) values for both eyes were reduced on average by 47%, 37%, 20% and 56% respectively. Finally, simulations proved that beam quality and lead thickness have little influence on eye dose while beam projection, the position and head orientation of the operator as well as the distance between the image detector and the patient are key parameters affecting eye and whole body doses.

Skin contamination with radiopharmaceuticals can occur during biomedical research and daily nuclear medicine practice as a result of accidental spills, after contact with bodily fluids of patients or by inattentively touching contaminated materials. Skin dose assessment should be carried out by repeated quantification to map the course of the contamination together with the use of appropriate skin dose rate conversion factors. Contamination is generally characterised by local spots on the palmar surface of the hand and complete decontamination is difficult as a result of percutaneous absorption. This specific issue requires special consideration as to the skin dose rate conversion factors as a measure for the absorbed dose rate to the basal layer of the epidermis. In this work we used Monte Carlo simulations to study the influence of the contamination area, the epidermal thickness and the percutaneous absorption on the absorbed skin dose rate conversion factors for a set of 39 medical radionuclides. The results show that the absorbed dose to the basal layer of the epidermis can differ by up to two orders of magnitude from the operational quantity Hp(0.07) when using an appropriate epidermal thickness in combination with the effect of percutaneous absorption.

The medical staff performing interventional cardiology and radiology (IC/IR) procedures stand close to the patient and thus close to the primary radiation beam. Although they wear a lead apron and thyroid collar, their hands, legs and eyes are not protected. Therefore, these parts could receive significantly high doses. Moreover, thedose ranges for the same kind of procedures vary a lot, as many factors affect extremity and eye lens doses. Additionally, there is evidence that eye lens doses can be high in IR/IC, and cases of cataract have been reported in recent years. A lack of an appropriate eye lens dosemeter as well as an appropriate calibration procedure has been identified. Medical staff in IR/IC could benefit from the use of active personal dosemeters (APDs) as optimisation tool. However, a lack of appropriate APDs is identified for typical fields in IR and IC. Very few devices can detect low energy fields, and none of them are really designed for working in pulsed radiation fields. In the field of nuclear medicine (NM) the extremity doses to the technologists are also known to be very high. One can highlight the difficulties in estimating the dose distribution across the hands, and the need for greater knowledge of doses received during the main tasks of a nuclear medicine department, especially using unsealed sources. The ORAMED project, (www.oramed-fp7.eu) was set up to optimize the working procedures in these medical fields with respect to radiation protection. ORAMED wasstructured in 5 work packages: - Extremity and eye lens dosimetry in IR and IC - Development of practical eye lens dosimetry - Optimization of the use of APDs in IR and IC - Extremity dosimetry in NM - Training and dissemination A coordinated measurement program in European hospitals was organised both in IR/IC and NM departments. Moreover, simulations of the most representative workplaces/procedures were performed to determine the main parameters that influence the extremity and eye lens doses. Some dedicated studies on improving the eye lens dosimetry and active personal dosimetry were conducted. Based on the measurement and simulation results, a series of practical guidelines and training packages were developed. The influence of the different radiation protection measures (like shields)in IR/IChave been quantified, and clear monitoring requirements have been formulated for a series of medical procedures. A formalism for the use of the operational quantity for eye lens dose measurements have been worked out (calibration phantom, conversion coefficients, type test procedures, ...). A dedicated eye lens dosemeter has been developed that can be used in routine monitoring. The different existing APDs have been tested in fields that are representative for hospital fields (like pulsed fields), and a series of guidelines for the use of these APDs in hospitals have been made. Also, an improved APD device specifically for IR/IC fields has been developed.The extensive measurement and simulation campaign for extremity doses in NM lead to a systematic evaluation of the different radiation protection measures. These are condensed in a series of practical guidelines to be used. The dose distribution across the hands of the technologists was characterised, and recommendations for routine monitoring have been formulated. The outcome of the ORAMED project will improve the radiation protection standards for medical staff. The systematic measurements and simulations are the new standards that will be used for many years to come. The practical guidelines that have been developed can be used in the hospitals by the medical staff. In particular, the developments on the eye-lens dosimetry and the active personal dosemeters will result in an improvement of the practical measurement capabilities in the field.

Measurements performed within the ORAMED project helped to evaluate the dose levels to the operators' hands, wrists, legs and eye lenses, during several types of interventional radiology (IR) and cardiology (IC) procedures, and also to determine the parameters that affect the doses. However, the study of the effect of each parameter separately, was possible only through Monte Carlo (MC) simulations, as in clinical practice many of those parameters change simultaneously. The influence of the protective equipment, the beam projections, the beam quality, the field size and the position of the operator according to the position of access of the catheter was investigated, using anthropomorphic phantoms in setups that represent realistic IR/IC procedures. The proper use of protective shields was found to be the most important way of reducing extremity and eye lens exposure during such examinations. Ceiling suspended shields can reduce the doses to the eye lenses up to 97%, but they can also reduce hand doses about 70% when placed correctly. The highest exposure to the operator is observed for left anterior oblique (LAO) and cranial projections. Additionally, for overcouch irradiations the eyes and the hands are about 6 times more exposed compared to the cases where the tube is below the operating table. For the lateral LAO projection, placing the ceiling suspended shield at the left side of the operator is twice more effective for the protection of the eyes compared to the cases where it is placed above the patient. Finally, beam collimation was found to play an important role in the reduction of the hands and wrists doses, especially when the operator is close to the irradiation field. © 2011 Elsevier Ltd. All rights reserved.

Purpose: The purpose of this study was to compare and validate three methods to simulate radiographic image detectors with the Monte Carlo software MCNP/MCNPX in a time efficient way. Methods: The first detector model was the standard semideterministic radiography tally, which has been used in previous image simulation studies. Next to the radiography tally two alternative stochastic detector models were developed: A perfect energy integrating detector and a detector based on the energy absorbed in the detector material. Validation of three image detector models was performed by comparing calculated scatter-to-primary ratios (SPRs) with the published and experimentally acquired SPR values. Results: For mammographic applications, SPRs computed with the radiography tally were up to 44% larger than the published results, while the SPRs computed with the perfect energy integrating detectors and the blur-free absorbed energy detector model were, on the average, 0.3% (ranging from -3% to 3%) and 0.4% (ranging from -5% to 5%) lower, respectively. For general radiography applications, the radiography tally overestimated the measured SPR by as much as 46%. The SPRs calculated with the perfect energy integrating detectors were, on the average, 4.7% (ranging from -5.3% to -4%) lower than the measured SPRs, whereas for the blur-free absorbed energy detector model, the calculated SPRs were, on the average, 1.3% (ranging from -0.1% to 2.4%) larger than the measured SPRs. Conclusions: For mammographic applications, both the perfect energy integrating detector model and the blur-free energy absorbing detector model can be used to simulate image detectors, whereas for conventional x-ray imaging using higher energies, the blur-free energy absorbing detector model is the most appropriate image detector model. The radiography tally overestimates the scattered part and should therefore not be used to simulate radiographic image detectors. © 2010 American Association of Physicists in Medicine.

The work package 3 of the ORAMED project, Collaborative Project (2008-11) supported by the European Commission within its seventh Framework Programme, is focused on the optimisation of the use of active personal dosemeters (APDs) in interventional radiology and cardiology (IR/IC). Indeed, a lack of appropriate APD devices is identified for these specific fields. Few devices can detect low-energy X rays (20-100 keV), and none of them are specifically designed for working in pulsed radiation fields. The work presented in this paper consists in studying the behaviour of some selected APDs deemed suitable for application in IR/IC. For this purpose, measurements under laboratory conditions, both with continuous and pulsed X-ray beams, and tests in real conditions on site in different European hospitals were performed. This study highlights the limitations of APDs for this application and the need of improving the APD technology so as to fulfil all needs in the IR/IC field.