Considerations of beta and electron transport in internal dose calculations. Progress report

The goal of this particular task is to consider, for the first time, the explicit transport of beta particles and photon-generated electrons in the series of six phantoms developed by Cristy and Eckerman (1987) at the Oak Ridge National Laboratory. In their report, ORNL/TM-8381, specific absorbed fractions of energy are reported for phantoms representing the newborn (3.4 kg), the one-year-old (9.8 kg), the five-year-old (19 kg), the ten-year-old (32 kg), the fifteen-year-old/adult female (55-58 kg), and the adult male (70 kg). Radiation transport calculations were performed with the Monte Carlo code ALGAMP which allows photon transport only. In subsequent calculations of radionuclide S values as is done in the MIRDOSE2 computer program, electron absorbed fractions are thus considered to be either unity or zero depending upon whether the source region does or does not equal the target region, respectively

Considerations of beta and electron transport in internal dose calculations. Final progress report, 1994--1998

This research focused on the following major tasks: improved dosimetric models of the head and brain; development of improved skeletal dosimetry models; development of dosimetric techniques for nonuniform activity distributions; pediatric dosimetry phantoms and radionuclide S values; microdosimetry of beta emitters in radioimmunotherapy; and mechanisms of molecular radiation damage

Adult male and female voxel-based models representing the ICRP reference man: The skeleton.

For the forthcoming update of organ dose conversion coefficients, the ICRP will use voxel-based computational phantoms due to their improved anatomical realism compared to the class of mathematical or stylized phantoms used previously. According to the ICRP philosophy, these phantoms should be representative of Reference Man with respect to their external dimensions, their organ topology, and their organ masses. To meet these requirements, reference models of an adult male and adult female have been constructed at the GSF, based on segmented tomographic image data sets of two individuals whose body height and weight closely resemble the ICRP Publication 89 reference values. A highly complex structure of the body is the skeleton, composed of cortical bone, trabecular bone, red and yellow bone marrow and endosteum (“bone surfaces” in their older terminology). The skeleton of the reference phantoms consists of 19 individually segmented bones and bone groups.  Sub-division of the bones into the above mentioned constituents would be necessary in order to allow a direct calculation of dose to red bone marrow and endosteum. However, the dimensions of the trabeculae, the cavities containing bone marrow, and the endosteum layer lining these cavities are clearly smaller than the resolution of a normal CT scan and, thus, these volumes could not be segmented in the tomographic images. As an attempt to represent the gross spatial distribution of these regions as realistically as possible at the given voxel resolution, 48 individual organ identification numbers were assigned to various parts of the skeleton: every segmented bone was subdivided in an outer shell of cortical bone and a spongious core; in the shafts of the long bones, a medullary cavity was additionally segmented. Using the data from ICRP Publication 89 on elemental tissue composition, from ICRU Report 46 on material mass densities, and from ICRP Publication 70 on the distribution of the red bone marrow among and marrow cellularity in individual bones, individual elemental compositions for these segmented bone regions were derived. Dose calculations using the thus provided skeletal source and target regions will be based on fluence-to-dose response functions that are multiplied with the particle fluence inside specific bone regions to give the dose quantities in the target tissues

Considerations of beta and electron transport in internal dose calculations

Ionizing radiation has broad uses in modern science and medicine. These uses often require the calculation of energy deposition in the irradiated media and, usually, the medium of interest is the human body. Energy deposition from radioactive sources within the human body and the effects of such deposition are considered in the field of internal dosimetry. In July of 1988, a three-year research project was initiated by the Nuclear Engineering Department at Texas A M University under the sponsorship of the US Department of Energy. The main thrust of the research was to consider, for the first time, the detailed spatial transport of electron and beta particles in the estimation of average organ doses under the Medical Internal Radiation Dose (MIRD) schema. At the present time (December of 1990), research activities are continuing within five areas. Several are new initiatives begun within the second or third year of the current contract period. They include: (1) development of small-scale dosimetry; (2) development of a differential volume phantom; (3) development of a dosimetric bone model; (4) assessment of the new ICRP lung model; and (5) studies into the mechanisms of DNA damage. A progress report is given for each of these tasks within the Comprehensive Report. In each case, preliminary results are very encouraging and plans for further research are detailed within this document

Voxel-based models representing the male and female ICRP reference adult--the skeleton.

For the forthcoming update of organ dose conversion coefficients, the International Commission on Radiological Protection (ICRP) will use voxel-based computational phantoms due to their improved anatomical realism compared with the class of mathematical or stylized phantoms used previously. According to the ICRP philosophy, these phantoms should be representative of the male and female reference adults with respect to their external dimensions, their organ topology and their organ masses. To meet these requirements, reference models of an adult male and adult female have been constructed at the GSF, based on existing voxel models segmented from tomographic images of two individuals whose body height and weight closely resemble the ICRP Publication 89 reference values. The skeleton is a highly complex structure of the body, composed of cortical bone, trabecular bone, red and yellow bone marrow and endosteum ('bone surfaces' in their older terminology). The skeleton of the reference phantoms consists of 19 individually segmented bones and bone groups. Sub-division of these bones into the above-mentioned constituents would be necessary in order to allow a direct calculation of dose to red bone marrow and endosteum. However, the dimensions of the trabeculae, the cavities containing bone marrow and the endosteum layer lining these cavities are clearly smaller than the resolution of a normal CT scan and, thus, these volumes could not be segmented in the tomographic images. As an attempt to represent the gross spatial distribution of these regions as realistically as possible at the given voxel resolution, 48 individual organ identification numbers were assigned to various parts of the skeleton: every segmented bone was subdivided into an outer shell of cortical bone and a spongious core; in the shafts of the long bones, a medullary cavity was additionally segmented. Using the data from ICRP Publication 89 on elemental tissue composition, from ICRU Report 46 on material mass densities, and from ICRP Publication 70 on the distribution of the red bone marrow among and marrow cellularity in individual bones, individual elemental compositions for these segmented bone regions were derived. Thus, most of the relevant source and target regions of the skeleton were provided. Dose calculations using these regions will be based on fluence-to-dose response functions that are multiplied with the particle fluence inside specific bone regions to give the dose quantities of interest to the target tissues

SU‐E‐I‐48: Cloud Computing for Interventional Fluoroscopy Dose Assessment

Purpose: To explore the application of cloud computing for quantifying and documenting patient radiation dose in interventional fluoroscopy. Methods: In this study, a framework has been developed for providing personalized Monte Carlo based dose reports for patients undergoing interventional fluoroscopic procedures. The framework is built around the DICOM Radiation Dose Structured Report (RDSR) and the ability to automatically translate the imbedded information into an input file for the MCNPX radiation transport code. A three‐step program was written to perform this task. The first step imports the RDSR and fills each row of a 2D array with the geometric and dose parameters connected to each irradiation event. The second step culls the array and summarizes the information into a limited number of irradiation events where geometric parameters for similar events are averaged and dose information summed. In the final step, each row of the summarized array is translated into an MCNPX input file by completing sections of a template file. An anthropometrically‐matched hybrid phantom selected from the UF patient‐dependent series is used to represent each patient. Initial testing was performed using twenty RDSRs received from Shands Jacksonville Medical Center. Monte Carlo simulation was executed on the ALRADS dosimetry cluster at the University of Florida, Gainesville. Results: The program successfully received twenty RDSRs via the internet and processed over 50 MCNPX input files. Detailed patient dose reports were returned on demand within 24 hours. Conclusions: While individual radiation transport is impractical within the clinic, a major technological shift has been towards internet‐based “cloud computing” where programs are run on off‐site servers accessed via the internet. In this environment and with the tools developed in this research, RDSRs can be uploaded from the clinic to the web and returned within a matter of hours as detailed radiation dose reports

Calculated yields of ammonia in the radiolysis of deoxygenated solutions of glycylglycine

This paper presents detailed Monte Carlo simulations of physical and chemical interactions occurring within electron tracks in deoxygenated solutions of glycylglycine. Hydrated electrons produced within these tracks react with the solute to produce ammonia and a peptide secondary free radical. Calculated yields of ammonia are presented for a range of solute concentrations and electron energies. Excellent agreement is found between calculated and measured yields of ammonia in solutions irradiated by 250-kVp x-rays and /sup 60/Co gamma rays. 12 refs., 5 figs

Dosimetric models of the eye and lens of the eye and their use in assessing dose coefficients for ocular exposures.

Based upon recent epidemiological studies of ocular exposure, the Main Commission of the International Commission on Radiological Protection (ICRP) in ICRP Publication 118 states that the threshold dose for radiation-induced cataracts is now considered to be approximately 0.5 Gy for both acute and fractionated exposures. Consequently, a reduction was also recommended for the occupational annual equivalent dose to the lens of the eye from 150 mSv to 20 mSv, averaged over defined periods of 5 years. To support ocular dose assessment and optimisation, Committee 2 included Annex F within ICRP Publication 116. Annex F provides dose coefficients - absorbed dose per particle fluence - for photon, electron, and neutron irradiation of the eye and lens of the eye using two dosimetric models. The first approach uses the reference adult male and female voxel phantoms of ICRP Publication 110. The second approach uses the stylised eye model of Behrens et al., which itself is based on ocular dimensional data given in Charles and Brown. This article will review the data and models of Annex F with particular emphasis on how these models treat tissue regions thought to be associated with stem cells at risk

Response functions for computing absorbed dose to skeletal tissues from photon irradiation.

The calculation of absorbed dose in skeletal tissues at radiogenic risk has been a difficult problem because the relevant structures cannot be represented in conventional geometric terms nor can they be visualised in the tomographic image data used to define the computational models of the human body. The active marrow, the tissue of concern in leukaemia induction, is present within the spongiosa regions of trabecular bone, whereas the osteoprogenitor cells at risk for bone cancer induction are considered to be within the soft tissues adjacent to the mineral surfaces. The International Commission on Radiological Protection (ICRP) recommends averaging the absorbed energy over the active marrow within the spongiosa and over the soft tissues within 10 microm of the mineral surface for leukaemia and bone cancer induction, respectively. In its forthcoming recommendation, it is expected that the latter guidance will be changed to include soft tissues within 50 microm of the mineral surfaces. To address the computational problems, the skeleton of the proposed ICRP reference computational phantom has been subdivided to identify those voxels associated with cortical shell, spongiosa and the medullary cavity of the long bones. It is further proposed that the Monte Carlo calculations with these phantoms compute the energy deposition in the skeletal target tissues as the product of the particle fluence in the skeletal subdivisions and applicable fluence-to-dose-response functions. This paper outlines the development of such response functions for photons