Animal models for medical countermeasures to radiation exposure.

Since September 11, 2001, there has been the recognition of a plausible threat from acts of terrorism, including radiological or nuclear attacks. A network of Centers for Medical Countermeasures against Radiation (CMCRs) has been established across the U.S.

The biological effectiveness of antiproton irradiation.

Background And Purpose: Antiprotons travel through tissue in a manner similar to that for protons until they reach the end of their range where they annihilate and deposit additional energy. This makes them potentially interesting for radiotherapy. The aim of this study was to conduct the first ever measurements of the biological effectiveness of antiprotons.

Investigations of a minimally invasive method for treatment of spinal malignancies with LINAC stereotactic radiation therapy: accuracy and animal studies.

Purpose: A new method for stereotactic irradiation of spinal malignancies is presented, with evaluations of the theoretic and practical limitations of localization accuracy and the implementation of the method in swine.

Materials And Methods: In a percutaneous procedure, a minimum of three small (1.7-mm-diameter) titanium markers are permanently affixed to a vertebra.

CT-based dosimetry calculations for 125I prostate implants.

Purpose: To evaluate the Monte Carlo code MCNP4B for low-energy brachytherapy calculations, including the effects of interseed attenuation and patient specific heterogeneities, on the calculated dose distribution from transperineal implantation of 125I.

Methods And Materials: The Monte Carlo code MCNP4B was used to model and benchmark the absolute dose distribution from two 125I brachytherapy seeds (model 6711 and 6702). Based upon the physical source model, the total photon intensity and differential energy spectrum were evaluated as a function of angle from the transverse bisector of the source.

Dose distributions using kilovoltage x-rays and dose enhancement from iodine contrast agents.

In x-ray phototherapy of brain tumours, the tumour is loaded with iodine and exposed to kilovoltage x-rays. Due to the high photoelectric cross sections of iodine, substantial photoelectric interactions occur. The flux of photoelectrons, characteristic x-rays and Auger electrons produce a localized dose enhancement.

Monte Carlo treatment planning for stereotactic radiosurgery.

Objectives: In radiosurgery treatment planning there is general acceptance that the target volume can be assumed to be homogeneous and that corrections for variations in contour are unnecessary. Thus, dose algorithms employed in radiosurgery treatment planning are quite unsophisticated; in almost every case the algorithms are the simple product of tissue-maximum and off-axis ratios and an output factor. In small photon beams, however, the lack of side scatter equilibrium compromises these assumptions.

Fractionated stereotactic radiotherapy: rationale and methods.

Stereotactic radiosurgery (SRS) has become a widely accepted technique for the treatment intracranial neoplasms. Combined with modern imaging modalities, SRS has established its efficacy in a variety of indications. From the outset, however, it was recognized that the delivery of a single large dose of radiation was essentially "bad biology made better by good physics.

A CT-based Monte Carlo simulation tool for dosimetry planning and analysis.

The Los Alamos code MCNP4A (Monte Carlo N-Particle version 4A) is currently used to simulate a variety of problems ranging from nuclear reactor analysis to boron neutron capture therapy. A graphical user interface has been developed that automatically sets up the MCNP4A geometry and radiation source requirements for a three-dimensional Monte Carlo simulation using computed tomography data. The major drawback for this dosimetry system is the amount of time to obtain a statistically significant answer.

Biologically effective dose distribution based on the linear quadratic model and its clinical relevance.

Purpose: Radiotherapy plans based on physical dose distributions do not necessarily entirely reflect the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work, we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model.

Implications of tissue heterogeneity for radiosurgery in head and neck tumors.

Purpose: This study was undertaken to investigate the perturbation of small radiation beams by low density heterogeneities and to evaluate the ability of a Monte Carlo code to account for such perturbation. Performance of an inexpensive film scanning system was also evaluated.

Methods And Materials: Film and diode measurements were made in an acrylic phantom in which the size and position of an air gap were varied.

A verification of the Monte Carlo code MCNP for thick target bremsstrahlung calculations.

The bremsstrahlung spectra from thick targets of Be, Al, and Pb are calculated using the Monte Carlo code MCNP (Monte Carlo N-particle). The current version of MCNP (v.4A) incorporates a coupled electron-photon transport scheme that allows the user to estimate the photon fluence produced from primary electron interactions.

Dose-survival curves, alpha/beta ratios, RBE values, and equal effect per fraction for neutron irradiation of jejunal crypt cells.

Jejunal crypt cell survival after regimens of one, two, three and five fractions was used to reconstruct composite single-dose survival curves for neutrons of five different energies. There is no obvious shoulder, but there is a gradual divergence from linearity that is most evident at low levels of cell survival (high doses). The effect of dose fractionation is relatively small, especially at the low doses characteristic of each treatment session in neutron radiotherapy.

Anthropomorphic radiation therapy phantoms: a quantitative assessment of tissue substitutes.

Compositional analyses of samples of soft tissue and lung substitutes used in the construction of anthropomorphic radiotherapy phantoms were performed for products from Alderson Research Laboratories Inc., Kyoto Scientific Specimens Company/Capintec Inc., Humanoid Systems Inc.

Radiation quality investigations around a neutron therapy beam, using a high-pressure ionization chamber.

The mean quality factor (Q) and the dose mean linear energy transfer [LET (LD)] a few centimeters outside a neutron therapy beam have been measured using a high-pressure ionization chamber. Measurements have been carried out in air, 5 and 100 cm outside the treatment field edge on the patient plane for p(46)-Be neurons and are compared with the results obtained at the same points with a low-pressure proportional counter (Rossi counter) and a Bonner spheres system. General agreement is found between these independent methods.

Adhesion formation in experimental chronic radiation enteropathy.

We have studied the late changes associated with radiation enteropathy in mice over a period of 224 days following single or split doses of gamma radiation delivered to the total abdomen (TAI). We focused on the importance of adhesion formation as a cause of strictures and gut-associated deaths following TAI. Gut-associated peritoneal adhesions were found in mice 2-7 months after receiving 13.

Comparison of the gastrointestinal syndrome after total-body or total-abdominal irradiation.

In pathogen-free mice, but not standard conventionally housed laboratory rodents, two distinctly different modes of early radiation lethality can be identified by modifying the irradiation technique (total-body versus abdominal irradiation) or by therapeutic intervention such as rescue of total-body-irradiated mice with syngeneic bone marrow or spleen. While damage to the gastrointestinal tract is usually designated as the predominant cause of death occurring within 10 days of radiation exposure, it was demonstrated that damage to the hematopoietic/lymphopoietic system can result in animal lethality over the same period as the gastrointestinal syndrome and that this target cell population is more radiation-sensitive than the gastrointestinal epithelium.

Uses of ionizing radiation and medical-care-related problems.

The uses of ionizing radiation in medicine are currently undergoing changes due to at least four major influences: (1) the constantly changing public perception of the hazards of radiation, (2) continuing technical innovation and development in equipment, (3) the imposition of diagnosis-related group funding by government health-care funding agencies, and (4) an increase in the average age of the U.S. population.

Skin-sparing effects of neutron beam filtering materials.

The skin-sparing effects of several filtering materials for fast neutron beams were studied under various conditions. A parallel-plate ionization chamber was used for the measurements. The parameters which were studied included field size, distance from filter to ion chamber, filter material, and filter thickness.

Verification timer for AECL 780 Cobalt unit.

To obtain verification of the proper time setting of the motorized run down timer for a AECL 780 Cobalt Unit, a digital timer is described, which can be added to the system for under $300.

Modification of the 50% maximum dose depth for 41-MeV (p+,Be) neutrons by use of filtration and/or transmission targets.

Several target configurations for the 41-MeV (p+,Be) reaction have been evaluated for the characteristics of the radiation field produced; depth dose, dose rate per microA, From analysis, it is concluded that to achieve the desired 13.2-cm depth for 50% of maximum dose and acceptable dose rate at a target-to-skin distance (TSD) of 125-150 cm, the neutron spectra must be filtered to preferentially absorb the lower-energy neutrons. Further increases in depth of 50% of maximum dose and a significant reduction in beryllium heating problems result if a partial transmission target is used with the terminal 30% of proton energy being deposited in a copper target backing.

Calorimetric and ionimetric dosimetry intercomparisons I: U.S. neutron radiotherapy centers.

In the U.S. neutron radiotherapy trial centers, absorbed dose is routinely measured using commercially available A-150 tissue equivalent (TE) plastic ionization chambers.

Lymphatic clearance of radioactive sulfur colloid.

Lymphatic clearance of radioactive sulfur colloid is measured in the hind limb of five mongrel dogs. A solid state Si(Li) detector is placed onto the skin to continuously record activity over the site of subcutaneous injection. Decrease in activity follows an exponential decay which is modeled as a dual decay occurring from both the radioactive decay of the tracer and the lymph clearance of the tagged sulfur colloid.

Neutron energy spectra of d(49)-Be and p(41)-Be neutron radiotherapy sources.

Zero-degree neutron energy spectra for the p(41)-Be and d(49)-Be reactions were measured by time-of-flight for neutrons with energies above 1.9 and 1.4 MeV, respectively.