Development of DynamicMC for PHITS Monte Carlo package.

Previously, we have developed DynamicMC for modeling relative movement of Oak Ridge National Laboratory phantom in a radiation field for the Monte Carlo N-Particle package (Health Physics. 2023,124(4):301-309). Using this software, three-dimensional dose distributions in a phantom irradiated by a certain mono-energetic (Mono E) source can be deduced through its graphical user interface. In this study, we extended DynamicMC to be used in combination with the Particle and Heavy Ion Transport code System (PHITS) by providing it with a higher flexibility for dynamic movement for an anthropomorphic phantom. For this purpose, we implemented four new functions into the software, which are (1) to generate not only Mono E sources but also those having an energy spectrum of an arbitrary radioisotope (2) to calculate the absorbed doses for several radiologically important organs (3) to automatically average the calculated absorbed doses along the path of the phantom and (4) to generate user-defined slab shielding materials. The first and third items utilize the PHITS-specific modalities named radioisotope-source and sumtally functions, respectively. The computational cost and complexity can be dramatically reduced with these features. We anticipate that the present work and the developed open-source tools will be in the interest of nuclear radiation physics community for research and teaching purposes.

The Benefits of Deploying Health Physics Specialists to Joint Operation Areas.

Preventive Medicine Specialists (military occupational specialty [MOS] 68S) with the health physics specialist (N4) qualification identifier possess a unique force health protection skill set. In garrison, they ensure radiation exposures to patients, occupational workers and the public from hospital activities such as radioisotope therapy and x-ray machines do not to exceed Federal law limits and kept as low as reasonably achievable. Maintaining sufficient numbers of health physics specialists (HPSs) to fill authorizations has been a consistent struggle for the Army Medical Department due to the rigorous academic requirements of the additional skill identifier-producing program. This shortage has limited MOS 68SN4 deployment opportunities in the past and prevented medical planners from recognizing the capabilities these Soldiers can bring to the fight. In 2014, for the first time, HPSs were sourced to deploy as an augmentation capability to the 172nd Preventive Medicine Detachment (PM Det), the sole PM Det supporting the Combined Joint Operations Area-Afghanistan. Considerable successes in bettering radiation safety practices and improvements in incident and accident response were achieved as a result of their deployment. The purposes of this article are to describe the mission services performed by HPSs in Afghanistan, discuss the benefits of deploying HPSs with PM Dets, and demonstrate to senior medical leadership the importance of maintaining a health physics capability in a theater environment.

[Medical Applications of the PHITS Code I: Recent Improvements and Biological Dose Estimation Model].

PHITS is a general purpose Monte Carlo particle transport simulation code developed through the collaboration of several institutes mainly in Japan. It can analyze the motion of nearly all radiations over wide energy ranges in 3-dimensional matters. It has been used for various applications including medical physics. This paper reviews the recent improvements of the code, together with the biological dose estimation method developed on the basis of the microdosimetric function implemented in PHITS.

32P brachytherapy conformal source model RIC-100 for high-dose-rate treatment of superficial disease: Monte Carlo calculations, diode measurements, and clinical implementation.

PURPOSE: A novel (32)P brachytherapy source has been in use at our institution intraoperatively for temporary radiation therapy of the spinal dura and other localized tumors. We describe the dosimetry and clinical implementation of the source. METHODS AND MATERIALS: Dosimetric evaluation for the source was done with a complete set of MCNP5 Monte Carlo calculations preceding clinical implementation. In addition, the depth dose curve and dose rate were measured by use of an electron field diode to verify the Monte Carlo calculations. Calibration procedures using the diode in a custom-designed phantom to provide an absolute dose calibration and to check dose uniformity across the source area for each source before treatment were established. RESULTS: Good agreement was established between the Monte Carlo calculations and diode measurements. Quality assurance measurements results are provided for about 100 sources used to date. Clinical source calibrations were usually within 10% of manufacturer specifications. Procedures for safe handling of the source are described. DISCUSSION: Clinical considerations for using the source are discussed.

[Features of PHITS and its application to medical physics].

PHITS is a general purpose Monte Carlo particle transport simulation code to analyze the transport in three-dimensional phase space and collisions of nearly all particles, including heavy ions, over wide energy range up to 100 GeV/u. Various quantities, such as particle fluence and deposition energies in materials, can be deduced using estimator functions "tally". Recently, a microdosimetric tally function was also developed to apply PHITS to medical physics. Owing to these features, PHITS has been used for medical applications, such as radiation therapy and protection.

Application of failure mode and effects analysis to intraoperative radiation therapy using mobile electron linear accelerators.

PURPOSE: Failure mode and effects analysis (FMEA) represents a prospective approach for risk assessment. A multidisciplinary working group of the Italian Association for Medical Physics applied FMEA to electron beam intraoperative radiation therapy (IORT) delivered using mobile linear accelerators, aiming at preventing accidental exposures to the patient. METHODS AND MATERIALS: FMEA was applied to the IORT process, for the stages of the treatment delivery and verification, and consisted of three steps: 1) identification of the involved subprocesses; 2) identification and ranking of the potential failure modes, together with their causes and effects, using the risk probability number (RPN) scoring system, based on the product of three parameters (severity, frequency of occurrence and detectability, each ranging from 1 to 10); 3) identification of additional safety measures to be proposed for process quality and safety improvement. RPN upper threshold for little concern of risk was set at 125. RESULTS: Twenty-four subprocesses were identified. Ten potential failure modes were found and scored, in terms of RPN, in the range of 42-216. The most critical failure modes consisted of internal shield misalignment, wrong Monitor Unit calculation and incorrect data entry at treatment console. Potential causes of failure included shield displacement, human errors, such as underestimation of CTV extension, mainly because of lack of adequate training and time pressures, failure in the communication between operators, and machine malfunctioning. The main effects of failure were represented by CTV underdose, wrong dose distribution and/or delivery, unintended normal tissue irradiation. As additional safety measures, the utilization of a dedicated staff for IORT, double-checking of MU calculation and data entry and finally implementation of in vivo dosimetry were suggested. CONCLUSIONS: FMEA appeared as a useful tool for prospective evaluation of patient safety in radiotherapy. The application of this method to IORT lead to identify three safety measures for risk mitigation.

MEDECOR--a medical decorporation tool to assist first responders, receivers, and medical reach-back personnel in triage, treatment, and risk assessment after internalization of radionuclides.

After a radiological dispersal device (RDD) event, it is possible for radionuclides to enter the human body through inhalation, ingestion, and skin and wound absorption. From a health physics perspective, it is important to know the magnitude of the intake to perform dosimetric assessments. From a medical perspective, removal of radionuclides leading to dose aversion (hence risk reduction) is of high importance. The efficacy of medical decorporation strategies is extremely dependent upon the time of treatment delivery after intake. The "golden hour," or more realistically 3-4 h, is optimal when attempting to increase removal of radionuclides from extracellular fluids prior to cellular incorporation. To assist medical first response personnel in making timely decisions regarding appropriate treatment delivery modes, it is desirable to have a software tool that compiles existing radionuclide decorporation therapy data and allows a user to perform simple diagnosis leading to optimized decorporation treatment strategies. In its most simple application, the software is a large database of radionuclide decorporation strategies and treatments. The software can also be used in clinical interactive mode, in which the user inputs the radionuclide, estimated activity, route of intake and time since exposure. The software makes suggestions as to the urgency of treatment (i.e., triage) and the suggested therapy. Current developments include risk assessment which impacts the potential risk of delivered therapy and resource allocation of therapeutic agents. The software, developed for the Canadian Department of National Defence (DND), is titled MEDECOR (MEdical DECORporation). The MEDECOR tool was designed for use on both personal digital assistant and laptop computer environments. The tool was designed using HTML/Jscript, to allow for ease of portability amongst different computing platforms. This paper presents the features of MEDECOR, results of testing at a major NATO exercise, and future development of this tool into MEDECOR2.

Design and verification of shielding for the advanced spent fuel conditioning process facility.

An Advanced spent fuel Conditioning Process Facility (ACPF) has recently been constructed by a modification of previously unused cells. ACPF is a hot cell with two rooms located in the basement of the Irradiated Materials Experiment Facility (IMEF) at the Korea Atomic Energy Research Institute. This is for demonstrating the advanced spent fuel conditioning process being proposed in Korea, which is an electrolytic reduction process of spent oxide fuels into a metallic form. The ACPF was designed with a more than 90 cm thick high density concrete shield wall to handle 1.38 PBq (37,430 Ci) of radioactive materials with dose rates lower than 10 muSv h in the operational areas (7,000 zone) and 150 muSv h in the service areas (8,000 zone). In Monte Carlo calculations with a design basis source inventory, the results for the bounding wall showed a maximum of 3 muSv h dose rate at an exterior surface of the ACPF for gamma radiation and 0.76 muSv h for neutrons. All the bounding structures of the ACPF were investigated to check on the shielding performance of the facility to ensure the radiation safety of the facility. A test was performed with a 2.96 TBq (80 Ci) 60Co source unit and the test results were compared with the calculation results. A few failure points were discovered and carefully fixed to meet the design criteria. After fixing the problems, the failure points were rechecked and the safety of the shielding structures was confirmed. In conclusion, it was confirmed that all the investigated parts of the ACPF passed the shielding safety limits by using this program and the ACPF is ready to fulfill its tasks for the advanced spent fuel conditioning process.

Fifty years of Monte Carlo simulations for medical physics.

Monte Carlo techniques have become ubiquitous in medical physics over the last 50 years with a doubling of papers on the subject every 5 years between the first PMB paper in 1967 and 2000 when the numbers levelled off. While recognizing the many other roles that Monte Carlo techniques have played in medical physics, this review emphasizes techniques for electron-photon transport simulations. The broad range of codes available is mentioned but there is special emphasis on the EGS4/EGSnrc code system which the author has helped develop for 25 years. The importance of the 1987 Erice Summer School on Monte Carlo techniques is highlighted. As an illustrative example of the role Monte Carlo techniques have played, the history of the correction for wall attenuation and scatter in an ion chamber is presented as it demonstrates the interplay between a specific problem and the development of tools to solve the problem which in turn leads to applications in other areas.

Methodology issues in epidemiological assessment of health effects of low-dose ionising radiation.

Epidemiological assessment of the health effects of exposure to low-dose ionising radiation is limited by the need for very large sample sizes and by various sources of bias that may generally affect epidemiological studies. Motivated by the present focus on low-dose effects, the following questions are examined: what are the strictly unavoidable limiting factors in the epidemiological methodology; what is its resolution limit in terms of effect size and what can be done to obtain further supportive evidence from the data?

An initial radiation safety needs assessment of Costa Rica: the South Texas Chapter of the Health Physics Society's strategic planning appraisal for participation in the "Radiation Safety Without Borders" initiative.

In response to the Health Physics Society's recent 'radiation safety without borders" initiative, the South Texas Chapter of the Health Physics Society selected Costa Rica as its partner country of choice. To develop an understanding of the radiation safety needs of this country, the fall 2001 University of Texas Health Science Center at Houston School of Public Health Environmental Radiation and Radioactivity class was tasked with the assignment of assessing the possible radiation safety needs and concerns for this country. The assignment culminated in a class presentation to the membership of the South Texas Chapter during its annual fall meeting. Using library and web based resources, tile students reviewed a number of public health and radiation-related topics. Life expectancies were found to be equivalent to the United States, even though significant differences in per capita health expenditures were noted. Costa Rica exhibited lower population mortality rates from major causes such as cardiovascular diseases, neoplasms, and external sources. Maternal and infant mortality rates were found to be much higher in Costa Rica than in the United States. Naturally occurring radiation sources such as uranium deposits were not identified as apparent major radiation issues of concern, although ultraviolet radiation exposures are consistently high. Several recent events in the country and the region involving patient overexposures suggest that concerns are likely focused on ensuring the proper use and maintenance of healing arts radiation equipment. The lack of available information on radioactive waste disposal suggests that waste handling also may be an issue warranting attention. The exercise proved to be very educational for the students, and the information gathered will serve to focus the Chapter's efforts when technical exchanges are initiated. The importance of linking this initiative to other existing programs within the country is also discussed.

Early dose assessment in criticality accidents.

Early estimation of dose is useful in the medical evaluation of severe radiation accidents. In a prior publication, lymphocyte depletion kinetics were shown to follow an exponential decline for gamma accidents in which the average whole-body dose was in the range 50 cGy < D < 8-10 Gy. In that study, the depletion rate constant was linearly related to dose, within the statistical variation of the historical hematological data. This simple technique has now been extended to include analysis of various types of criticality accidents (liquid process; water moderated systems; metallic systems). Lymphocyte depletion in high-level mixed gamma/neutron accidents is found to be approximately equal, at a given effective dose, to that for gamma accidents. This universality would indicate a neutron RBE for human lymphocytes close to unity. Furthermore, the technique appears to be insensitive to the shape of gamma and neutron spectra, therefore making it especially robust for initial, approximate dose estimation.

Conversion coefficients based on the VIP-Man anatomical model and EGS4.

A new set of conversion coefficients from kerma free-in-air to absorbed dose and kerma free-in-air to "effective VIP-Man dose" has been calculated for external monoenergetic photon beams from 10 keV to 10 MeV using an image-based whole-body anatomical model. This model, called VIP-Man, was recently developed at Rensselaer from the high-resolution color images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently process the extremely large image data in VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic geometries. Conversion coefficients from this study are compared with those obtained from two mathematical models, ADAM and EVA. "Effective VIP-Man doses" differ from the previously reported effective dose results by 10%-50% for photons between 100 keV and 10 MeV. Discrepancies are more significant at lower energies and for individual organ doses. Since VIP-Man is a realistic model that contains several tissues that were not previously defined well (or not available) in other models, the reported results offer an opportunity to improve the existing dosimetric data and the mathematical models.

Evaluation and ranking of restoration strategies for radioactively contaminated sites.

An international project, whose aim was the development of a transparent and robust method for evaluating and ranking restoration strategies for radioactively contaminated sites (RESTRAT), was carried out under the Fourth Framework of the Nuclear Fission Safety Programme of the EU. The evaluation and ranking procedure used was based on the principles of justification and optimisation for radiation protection. A multi-attribute utility analysis was applied to allow for the inclusion of radiological health effects, economic costs and social factors. Values of these attributes were converted into utility values by applying linear utility functions and weighting factors, derived from scaling constants and expert judgement. The uncertainties and variabilities associated with these utility functions and weighting factors were dealt with by a probabilistic approach which utilised a Latin Hypercube Sampling technique. Potentially relevant restoration techniques were identified and their characteristics determined through a literature review. The methodology developed by this project has been illustrated by application to representative examples of different categories of contaminated sites; a waste disposal site, a uranium tailing site and a contaminated freshwater river.

Specific absorbed fractions from the image-based VIP-Man body model and EGS4-VLSI Monte Carlo code: internal electron emitters.

VIP-Man is a whole-body anatomical model newly developed at Rensselaer from the high-resolution colour images of the National Library of Medicine's Visible Human Project. This paper summarizes the use of VIP-Man and the Monte Carlo method to calculate specific absorbed fractions from internal electron emitters. A specially designed EGS4 user code, named EGS4-VLSI, was developed to use the extremely large number of image data contained in the VIP-Man. Monoenergetic and isotropic electron emitters with energies from 100 keV to 4 MeV are considered to be uniformly distributed in 26 organs. This paper presents, for the first time, results of internal electron exposures based on a realistic whole-body tomographic model. Because VIP-Man has many organs and tissues that were previously not well defined (or not available) in other models, the efforts at Rensselaer and elsewhere bring an unprecedented opportunity to significantly improve the internal dosimetry.

A comparison between default EGS4 and EGS4 with bound Compton cross sections when scattering occurs in bone and fat.

Computer simulation packages are important tools in understanding how radiation interacts with matter. EGS4 is a photon/electron Monte Carlo transport program that is employed in the health/medical physics field. Due to its high energy roots, the default version of EGS4 treats all electrons as unbound and therefore uses the Klein-Nishina cross section formula to determine Compton scattering angle distributions and the probability of Compton scattering through the branching ratio. Researchers have created improvements to EGS4 that account for the bound Compton cross section as well as other scattering properties. Numerical experiments were performed on both the default code and modified EGS4 to examine output differences in low Z materials such as fat and bone. Four incident photon energies were considered. At higher energies (500 keV and 1 MeV) the default and modified EGS4 codes produced results within 2sigma of one another. At 50 and 100 keV differences in scattering angle distribution and branching ratio values were found. In addition, the number of photoelectric absorptions and Compton scatters were also different at these energies.

Methodology for determining action levels for clean-up contaminated urban and agricultural environments.

A methodology for determining justified action levels for clean-up of contaminated environments has been elaborated based upon dose reductions and monetary costs associated with the clean-up or remedial measures. Action levels can be expressed as dose or contamination levels above which clean-up is justified and below which it is not. This paper discusses the factors needed to determine such action levels. The most important of these factors are the efficiency of the clean-up and the monetary costs of the clean-up operation. Examples of justified action levels for clean-up of urban and agricultural environments have been determined from uncertainty analyses. With selected parameter distributions for clean-up of urban and semi-urban environments, justified action levels for clean-up are found to be in the range of about 1-10 mSv y(-1). With selected parameter distributions for agricultural countermeasures, action levels for reduction of activity content in milk have been determined to be from less than 100 Bq L(-1) up to a few thousand Bq L(-1), corresponding to residual individual ingestion doses of about 0.1-0.5 mSv y(-1). The presented methodology, which can be extended to include more complex environments, can in a simple way give the decision maker an indication of when it is justified to clean a contaminated environment.

Using EGS4 Monte Carlo in medical radiation physics.

Monte Carlo modelling of particle transport problems in medical radiation physics offers significant advantages over other techniques. Experiments can be performed without having to set up the physical situation, and "impossible" experiments can be performed, such as labelling multiple-scattered particles or simulating the effect of chamber walls on dosimetry. The availability of standardised Monte Carlo packages (EGS4 and ETRAN/ITS), along with the development of more powerful and inexpensive computers has allowed more widespread use of the technique. This report discusses the principles of Monte Carlo modelling in general, then examines the EGS4 Monte Carlo package in more detail, with particular reference to its use in medical physics applications.