RFPID: development and 3D-printing of a female physical phantom for whole-body counter.

Whole-body counters (WBC) are used in internal dosimetry forin vivomonitoring in radiation protection. The calibration processes of a WBC set-up include the measurement of a physical phantom filled with a certificate radioactive source that usually is referred to a standard set of individuals determined by the International Commission on Radiological Protection (ICRP). The aim of this study was to develop an anthropomorphic and anthropometric female physical phantom for the calibration of the WBC systems. The reference female computational phantom of the ICRP, now called RFPID (Reference Female Phantom for Internal Dosimetry) was printed using PLA filament and with an empty interior. The goal is to use the RFPID to reduce the uncertainties associated within vivomonitoring system. The images which generated the phantom were manipulated using ImageJ®, Amide®, GIMP®and the 3D Slicer®software. RFPID was split into several parts and printed using a 3D printer in order to print the whole-body phantom. The newly printed physical phantom RFPID was successfully fabricated, and it is suitable to mimic human tissue, anatomically similar to a human body i.e., size, shape, material composition, and density.

Virtual calibration for in vivo measurement of Pb-210 activity in the skull using BOMAB, MIRD, and MIDA phantoms.

The counting efficiency calibration for in vivo measurement is crucial to derive the activity of radionuclides residing inside a monitored subject. Recently, virtual calibration based on computational phantoms has become popular, yet some key questions remain unresolved. Here, we focus on the in vivo measurement of Pb-210 in the skull and systematically examine how virtual calibration compares to those using physical phantoms and how the variety of computational phantoms affects the derived counting efficiency. It is found that the virtually calibrated efficiency based on the MIDA phantom, which characterizes the highest anatomical fidelity, shows reasonable consistency with the experimental counterpart, with a relative bias of approximately 10%. However, in comparison to the case based on the MIDA phantom, those based on the BOMAB and MIRD phantoms show larger deviation, demonstrating underestimations on the counting efficiency by 51% and 42%, respectively. This finding underscores the critical role of computational phantoms in the virtual calibration. This study contributes to the development of techniques for assessing lung cancer risk resulting from chronic radon exposure through in vivo measurement of skeletal Pb-210 activity.

Occupational internal monitoring in nuclear medicine service of Sainte-Anne military hospital: previous considerations and results.

The Nuclear Medicine Department of Sainte-Anne military hospital in Toulon uses 99mTc, 123I and 18F unsealed sources to provide therapeutic and diagnostic care. For a few years, only ambient air and surface monitoring were performed to check the absence of internal contamination risk for workers. To verify this risk assessment hypothesis, confirmatory monitoring programme including in vivo and in vitro measurements was performed by the French defence radiation protection service (SPRA, Clamart). Here, due to the short half-life of targeted radionuclides, the analytical sensitivity was determined with estimations of minimal detectable activities and derived recording levels. It was shown that sensitivity was sufficient to detect an internal contamination leading to an effective dose of 0.1 mSv for few days post intake. At the same time, around 20 whole-body countings were performed. Results were below minimal detectable activity and were confirmed by 24-hours urine analysis. So, actual working conditions do not lead to measurable internal contamination for nuclear medicine staff.

Monte Carlo calculation of whole body counter efficiency factors for different computational phantoms.

Individual monitoring can provide an estimate of the radioactivity present in the body of the exposed individuals. Periodic monitoring of occupationally exposed individuals is of great importance in case of accidental incorporation. Computational phantoms and Monte Carlo codes are often used to complement the calibration method of counting systems in internal dosimetry. Here, counting efficiency (CE) factors for a WBC system were calculated using MC simulations. The WBC system with a NaI(Tl) detector and the BOMAB phantom was modeled using three MC codes. After validation, the models were used to obtain CE values for a wide range of energies, and a CE curve was generated for the WBC system. To estimate the effects of anatomical differences on the measurement process, two anthropomorphic voxel phantoms were modeled using the VMC code. For the detector position with the highest CE value, the differences when comparing BOMAB results with the MaMP and Yale results were (-1 ± 6)% and (-1 ± 3)%, respectively. The results confirm that the use of the BOMAB phantom is a good approach for the calibration of the whole-body counter system. Measurements should be made at detector position with the highest CE values, and it is recommended to use the mean Monte Carlo CE values calculated in this work.

Production of sealed rod sources made from epoxy resin for the Saint-Petersburg brick phantom for the calibration of whole-body counters.

Rod sources are a common tool for the calibration of whole-body counters in combination with the Saint-Petersburg brick phantom. Here, a method for the production of such sources in ordinary radiochemical laboratories is presented. The rod sources consist of a tubular capsule of rigid polyvinyl chloride with a radioactive filling of epoxy resin. The method allows the production of rod sources at material costs of about 1 € per rod source and of ten rod sources by one person per day. Quality-assurance measurements were performed regarding the spatial distribution of the activity within the rod sources and the distribution of the activity throughout a set of sources. The relative double standard deviation of the activities of five different segments of single rod sources was 7.1%. The relative double standard deviation within a set of 90 rod sources was 2.8% after those 11% of sources with the greatest deviation from the arithmetic mean were discarded. Tests according to ISO 2919 to certify the rod sources as sealed sources of Class 2 of this standard were successfully conducted. The bending test proved to be the most critical test for the rod sources; the sources were broken by a mass of 12-14 kg, which is only slightly more than the stipulated mass of 10.2 kg. The presented method allows for a cost- and labour-effective production of sealed radioactive rod sources and thus facilitates the application of the Saint-Petersburg brick phantom for calibrations and interlaboratory comparisons of whole-body counters.

Testing Decision Level (DL) and Minimum Detectable Amount (MDA) for Hanford In Vivo Counting Systems.

ABSTRACT: Testing the decision level (DL) and minimum detectable amount (MDA) of a radionuclide for a direct bioassay (in vivo) counting system is a requirement for in vivo monitoring programs across the DOE complex. Bottle manikin absorption (BOMAB) and torso phantoms are used in conjunction with point sources to facilitate the testing. This paper describes a method of testing the DL and MDA values of in vivo counting systems with equipment commonly used by in vivo programs. This method is cost effective and minimizes waste since the radiological sources used can have broad ranges for decay activities. The results from the testing indicated that the current DL and MDA values are valid for the equipment and methods used at the Hanford in vivo counting facility.

Intake Ratio of 131I to 137CS Derived from Thyroid and Whole-body Doses to Residents of Iwaki City in Japan's Fukushima Prefecture.

ABSTRACT: It is very important to determine the precise internal thyroid doses of Fukushima residents involved in the 2011 Fukushima nuclear disaster, particularly for small children. This has been challenging due to the lack of direct human measurements to identify 131I, the biggest contributor to the thyroid doses. We previously used a dataset of late whole-body counter (WBC) measurements targeting 134Cs and 137Cs for the thyroid dose estimation in comparison with the intake ratios of 131I to 137Cs (or 134Cs) derived from thyroid and whole-body doses individually obtained from different subject groups, assuming simultaneous acute intake via inhalation. Herein, we applied the same method to the doses of residents in Iwaki city (located south of the Fukushima Daiichi Nuclear Power Plant) with a relatively high activity ratio (131I/137Cs) for the ground deposition density. Our analyses revealed that the intake ratio (131I/137Cs) for the Iwaki residents was 4.2-4.3, which is relatively consistent with the values obtained in other studies (average 3.0-5.0). No regional difference in the intake ratios from other areas was observed, but further studies are required to determine the accurate intake ratio in the early phase of the accident, in particular focusing on the reasonable interpretation of results of the late WBC measurements to evaluate the actual Cs intake.

RADIOISOTOPE DIAGNOSTIC ALGORITHM FOR THE RELAPSE AND METASTASES DETECTION IN THE IODINE-NEGATIVE DIFFERENTIATED THYROID CANCER. / RADIONUKLIDNYI DIAGNOSTYChNYI ALGORYTM DLIa VYIaVLENNIa RETsYDYVIV I METASTAZIV U KhVORYKh Z IOD-NEGATYVNYMY FORMAMY DYFERENTsIIOVANOGO RAKU ShchYTOPODIBNOÏ ZALOZY.

OBJECTIVE: Developing of algorithm for the post-surgical management of patients with iodine-negative metastasesof differentiated thyroid cancer (DTC). MATERIALS AND METHODS: The DTC patients with iodine-negative metastases (n = 115) were enrolled in the study.Of them the whole body scintigraphy (WBS) was performed with technetium-99m-hexakis-2-methoxyisobutylisonitrile(99mTc-MIBI) (n = 30), WBS with technetium-99m dimercaptosuccinic acid (99mTc-DMSA) (n = 30), 18FDG PET (n = 30), andcomputer tomography (CT-scan) (n = 25). Complex 99mTc-pertechnetate scans including the dynamic and static scintigraphy was performed supplementary to 99mTc-MIBI WBS in 10 patients to obtain the angiographic curves from DTCmetastatic foci. The non-radioiodine radiopharmaceutical technologies, namely the labeled 99mTc-MIBI, 99mTc-DMSA, 99mTc-pertechnetate, and 18FDG were applied to detect the iodine-negative DTC metastases. Radioisotopic examinationswere performed at the dual-head gamma camera (Mediso Medical Imaging Systems Ltd., Hungary) and single photonemission computed tomography (SPECT) scanner «E.CAM¼ (Siemens, Germany). PET/CT scans were performed on the«Biograph 64 TruePoint¼ imaging platform (Siemens, Germany) in accordance with the European Association of NuclearMedicine (EANM) recommendations for the Siemens imaging devices with 3D-mode data acquisition. RESULTS: The conducted research suggested that it is feasible to use the non-radioiodine (99mTc-MIBI and 99mTc-DMSA)radiopharmaceutical technologies to detect the iodine-negative DTC metastases. 18FDG PET is a highly informativetechnology for the detection of iodine-negative DTC metastases in case of lung involvement in the process. Compareof the non-radioiodine radiopharmaceuticals, CT scan and 18FDG-PET/CT indicated the highest sensitivity of 18FDGPET/CT (p < 0.05). WBS with 99mTc-MIBI and 99mTc-DMSA featured the highest specificity (100 %, p < 0.05). X-ray CTis marked by the significantly lower either sensitivity, specificity, and accuracy rate (p > 0.05). Developing andapplication of algorithm for the post-surgical management of patients with iodine-negative forms of DTC will allowfor the betimes detection of relapses and metastases with administration of adequate surgical, radiation, and targeted treatment. CONCLUSIONS: Obtained results offer the opportunity to optimize the post-surgical management of patients withiodine-negative DTC forms using the options of radionuclide diagnostics with non-radioiodine radiopharmaceuticals. The latter are readily available providing the cost-cutting of diagnostic support in these patients. Place ofmorphological methods of diagnosis is determined and stage of monitoring of patients with the iodine-negativemetastases is established. Possibility of the 18FDG-PET tests for the early diagnosis of iodine-negative metastases inDTC for the first time have been studied and substantiated in Ukraine. A comprehensive radiation algorithm for thelong-term monitoring of this category of patients will allow the timely detection of recurrences and metastases ofDTC and appropriate surgery, radiation and targeted therapy administration. Data obtained as a result of the studyallowed to improve the overall and recurrence-free survival rates in the able-bodied DTC patients and reduce thecosts of follow-up of patients with iodine-negative forms of DTC.

Whole-body protein kinetics in critically ill patients during 50 or 100% energy provision by enteral nutrition: A randomized cross-over study.

BACKGROUND: Enteral nutrition (EN) is a ubiquitous intervention in ICU patients but there is uncertainty regarding the optimal dose, timing and importance for patient-centered outcomes during critical illness. Our research group has previously found an improved protein balance during normocaloric versus hypocaloric parenteral nutrition in neurosurgical ICU patients. We now wanted to investigate if this could be demonstrated in a general ICU population with established enteral feeding, including patients on renal replacement therapy. METHODS: Patients with EN >80% of energy target as determined by indirect calorimetry were randomized to or 50% or 100% of current EN rate. After 24 hours, whole-body protein kinetics were determined by enteral and parenteral stable isotope tracer infusions. Treatment allocation was then switched, and tracer investigations repeated 24 hours later in a crossover design with patients serving as their own controls. RESULTS: Six patients completed the full protocol. During feeding with 100% EN all patients received >1.2 g/kg/day of protein. Mean whole-body protein balance increased from -6.07 to 2.93 µmol phenylalanine/kg/h during 100% EN as compared to 50% (p = 0.044). The oxidation rate of phenylalanine was unaltered (p = 0.78). CONCLUSIONS: It is possible to assess whole-body protein turnover using a stable isotope technique in critically ill patients during enteral feeding and renal replacement therapy. Our results also suggest a better whole-body protein balance during full dose as compared to half dose EN. As the sample size was smaller than anticipated, this finding should be confirmed in larger studies.

Person-specific calibration of a partial body counter used for individualised Am241skull measurements.

Incorporation of bone seeking alpha-emitting radionuclides such as241Am are of special concern, due to the potential of alpha particles to damage the extremely radiation-sensitive bone marrow. In the case of an internal contamination with241Am, directin vivomeasurements using Gamma-detectors are typically used to quantify the incorporated activity. Such detectors need to be calibrated with an anatomical phantom, for example of the skull, of known241Am activity that reproduces the anatomy of the measured individual as closely as possible. Any difference in anatomy and material composition between phantom and individual will bias the estimation of the incorporated activity. Consequently, in this work the impact of the most important anatomical parameters on detection efficiency of one of the germanium detectors of the Helmholtz Center Munich (HMGU) partial body counter were systematically studied. For that a detailed model of the germanium detector was implemented in the Monte Carlo codes GEANT4 and MCNPX. To simulate the detector efficiency, various skull voxel phantoms were used. By changing the phantom dimensions and geometry the impact of parameters such as shape and size of the skull, thickness of tissue covering the skull bone, distribution of241Am across the scull and within the skull bone matrix, on the detector efficiency was studied. Approaches to correct for these parameters were specifically developed for three physical skull phantoms for which Voxel phantoms were available: Case 102 USTUR phantom, Max-06 phantom, BfS phantom. Based on the impact of each parameter, correction factors for an 'individual-specific' calibration were calculated and applied to a real241Am contamination case reported in 2014. It was found that the incorporated241Am activity measured with the HMGU partial body counter was about twice as large as that estimated when using the BfS skull phantom without applying any correction factor for person-specific parameters. It is concluded that the approach developed in the present study should in the future be applied routinely for skull phantom measurements, because it allows for a considerably improved reconstruction of incorporated241Am using partial body counters.

Deconvolution of bulk blood eQTL effects into immune cell subpopulations.

BACKGROUND: Expression quantitative trait loci (eQTL) studies are used to interpret the function of disease-associated genetic risk factors. To date, most eQTL analyses have been conducted in bulk tissues, such as whole blood and tissue biopsies, which are likely to mask the cell type-context of the eQTL regulatory effects. Although this context can be investigated by generating transcriptional profiles from purified cell subpopulations, current methods to do this are labor-intensive and expensive. We introduce a new method, Decon2, as a framework for estimating cell proportions using expression profiles from bulk blood samples (Decon-cell) followed by deconvolution of cell type eQTLs (Decon-eQTL). RESULTS: The estimated cell proportions from Decon-cell agree with experimental measurements across cohorts (R ≥ 0.77). Using Decon-cell, we could predict the proportions of 34 circulating cell types for 3194 samples from a population-based cohort. Next, we identified 16,362 whole-blood eQTLs and deconvoluted cell type interaction (CTi) eQTLs using the predicted cell proportions from Decon-cell. CTi eQTLs show excellent allelic directional concordance with eQTL (≥ 96-100%) and chromatin mark QTL (≥87-92%) studies that used either purified cell subpopulations or single-cell RNA-seq, outperforming the conventional interaction effect. CONCLUSIONS: Decon2 provides a method to detect cell type interaction effects from bulk blood eQTLs that is useful for pinpointing the most relevant cell type for a given complex disease. Decon2 is available as an R package and Java application (https://github.com/molgenis/systemsgenetics/tree/master/Decon2) and as a web tool (www.molgenis.org/deconvolution).

Iodine contrast-to-noise ratio improvement at unit dose and contrast media volume reduction in whole-body photon-counting CT.

PURPOSE: To assess the dose-normalized iodine contrast-to-noise-ratio (CNRD) improvement and contrast media reduction potential obtained with photon-counting (PC) CT compared to conventional energy-integrating (EI) CT as a function of patient size and tube voltage. METHOD: Images of a semi-anthropomorphic phantom of different sizes (small, medium, large) equipped with vials containing different iodine concentrations were acquired at the SOMATOM CounT prototype CT system using tube voltages of 80 kV-140 kV. CNRD is evaluated in reconstructions obtained using the EI detector, the PC detector using a single bin, and in reconstructions obtained by statistically optimally weighting acquisitions with two bins. Iodine CNRD improvements, potential dose reduction and the potential contrast media volume reduction are reported. RESULTS: In general, iodine CNRD improvement increases with increasing tube voltage for all patient sizes. In particular, if only one energy bin is used, the CNRD improvement is up to 30 % (small: 10 %, medium: 18 %, large: 30 %) and up to 37 % if an optimal weighting of two bins is performed (small: 13 %, medium: 25 %, large: 37 %) which is equivalent to the potential contrast media volume reduction. The improved iodine CNRD of PC compared to EI may allow for a potential radiation dose reduction of up to 46 %. CONCLUSIONS: All patients' iodine contrast at given x-ray dose, and particularly medium and large sized patients acquired at higher tube voltages, may benefit from photon-counting CT. The iodine contrast improvement can be used to reduce patient dose or to reduce the amount of contrast agent that is administered.

In vivo measurement of pre-operational spallation source workers: baseline body burden levels and detection limits of relevant gamma emitters using high-resolution gamma spectrometry.

As a measure to prepare for long-term internal dose monitoring of workers at the European Spallation Source (ESS) in Lund, Sweden, operated by the European Research Infrastructure Consortium (ERIC), as well as to enhance emergency preparedness against accidental releases, a series of in vivo measurements were conducted using a high-resolution HPGe detector with a 123% relative efficiency (1.332 MeV). This study describes the whole-body counting set-up, calibration procedure, and subsequent validation measurements using conventional NaI(Tl)-scanning-bed geometry on a selection of workers from the ESS. Detection limits for the relevant gamma emitters 7Be, 172Hf, and 182Ta were determined to be 65 Bq, 130 Bq, and 22 Bq, respectively, using a 2400 s acquisition time. The baseline measurements suggest that care must be taken to ensure that the fluctuations in the presence of radon daughters 214Bi and 214Pb are minimised by, for example, ensuring a minimum air exchange between the measuring room and the ambient air, and by demanding that the measured subjects change clothes and shower before measurement. Furthermore, in a monitoring program for internal doses to spallation source workers, the presence of radionuclides originating from non-work-related sources (such as 226Ra from private water wells or 137Cs from intakes of Chernobyl contaminated foodstuffs), or radionuclides from previous work history (such as 60Co within the nuclear power industry), must be considered.

OCCUPATIONAL EYE LENS DOSE ESTIMATED USING WHOLE-BODY DOSEMETER IN INTERVENTIONAL CARDIOLOGY AND RADIOLOGY: A MONTE CARLO STUDY.

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.

TYPE TESTING OF LiF:Mg,Cu,P (TLD-100H) WHOLE-BODY DOSEMETERS FOR THE ASSESSMENT OF Hp(10) AND Hp(0.07).

In this work, the initial results of the type testing of the LiF:Mg,Cu,P (TLD-100H) whole-body personal dosemeters are presented. An assessment of reproducibility, linearity of the response, the residual signal as a function of the dose, energy and angular dependence of the response was performed. In general, the dosemeters show good reproducibility for different dose values and a linear behaviour for a range between 0.1 and 300 mSv. The detection limits obtained are lower than 50 µSv. The system presents a good energy and angular response for different radiation qualities.

RECOMMENDATIONS FOR MONITORING AND INTERNAL DOSIMETRY FOR NUCLEAR MEDICINE STAFF EXPOSED TO RADIOPHARMACEUTICALS 223Ra DICHLORIDE.

223Ra is a radiopharmaceutical used as unsealed source in nuclear medicine. In the case of staff inhalation contamination of 223Ra, methods to estimate the committed effective dose should be chosen with care. Three methods are available: whole-body measurement and gamma spectrometry for urine or faeces samples. Considering the analytical performances and uncertainties of these three methods, we propose recommendations for special dose assessment. As a first choice, due to its rapidity and its non-invasiveness, an in vivo analysis (with HPGe detector) is the most appropriate method. However, after 24 h, whole-body counting is not sensitive enough to detect a minimum effective dose of 1 mSv. Sufficient sensitivity can only be reached up to 8 days after contamination by true 24 h faeces samples analyses. Thus, despite its main drawbacks, this method appears to be more appropriate than urine to estimate the committed effective dose in addition to whole-body counting.

Experiences of Population Monitoring Using Whole-Body Counters in Response to the Fukushima Nuclear Accident.

Whole-body counter measurements of residents of Fukushima Prefecture have been extensively performed after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These measurements have demonstrated that the levels of internal contamination with radioactive cesium (Cs and Cs) in the residents are very low. This article provides an overview of and lessons learned from these whole-body counter measurements with emphasis on the technical problems encountered, and it discusses the effective use of whole-body counters for assessing the internal thyroid doses of individuals when direct measurements of I in the thyroid are difficult or impossible to implement for the total affected population in a short time after a nuclear reactor accident. The application of this dose reconstruction method requires determining the intake ratio of I to cesium isotopes at appropriate times and considers the short biological half-lives of cesium isotopes, in particular for children.

METHODOLOGY AT CIEMAT WHOLE BODY COUNTER FOR IN VIVO MONITORING OF RADIOIODINE IN THE THYROID OF EXPOSED POPULATION IN CASE OF NUCLEAR EMERGENCY.

Iodine-131 is one of the main concerns from the point of view of radiological protection in a short term after a nuclear accident. The WBC Laboratory of CIEMAT has developed a methodology for in vivo monitoring of radioiodine in the thyroid of exposed individuals in case of emergency. Thyroid-neck phantoms of different sizes are required for calibrating the detection systems in appropriate counting geometries for the measurement of exposed population. A Low-Energy Germanium (LEGe) detector and a Fastscan Counter were calibrated using a set of thyroid phantoms fabricated by CIEMAT. Each neck phantom consists of a Lucite cylinder with a vial source of 131I. Counting efficiencies depending on age and thyroid sizes were obtained to be used to determine the activity of 131I in internally contaminated people. DL of 131I varies with the age, being in the range of 5-8 Bq for the LEGe detector and 26-42 Bq for the Fastscan. Detection of intakes resulting in Committed Effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming a scenario of acute inhalation or ingestion of 131I by members of the public.

RETENTION OF 7Be IN THE LUNGS FOLLOWING INTAKE BY INHALATION.

Several workers were internally exposed to 7Be particles following their dispersion in air from a damaged electrodeposited source. A series of in vivo measurements performed with one worker up to 108 days post exposure determined that retention of 7Be in the thoracic region of the respiratory tract was best described by a two-component exponential function with half-lives of ~0.4 and ~109 days. The initial deposition in the thoracic region was estimated to be 6.8 kBq. The concentration of 7Be in single void urine samples collected from this worker up to 3 days post intake ranged from 1 to 10 Bq/l. In the absence of specific knowledge about the physical and chemical characteristics of the inhaled particles, the committed effective dose was estimated to be 0.3 µSv.

MCNPX CALCULATIONS OF SPECIFIC ABSORBED FRACTIONS IN SOME ORGANS OF THE HUMAN BODY DUE TO APPLICATION OF 133Xe, 99mTc and 81mKr RADIONUCLIDES.

Monte Carlo simulations were performed to evaluate treatment doses with wide spread used radionuclides 133Xe, 99mTc and 81mKr. These different radionuclides are used in perfusion or ventilation examinations in nuclear medicine and as indicators for cardiovascular and pulmonary diseases. The objective of this work was to estimate the specific absorbed fractions in surrounding organs and tissues, when these radionuclides are incorporated in the lungs. For this purpose a voxel thorax model has been developed and compared with the ORNL phantom. All calculations and simulations were performed by means of the MCNP5/X code.