Function Of Post-irradiation Time Research Articles

Response investigation of a new polymer gel dosimeter based on ammonium salt through MRI technique

Increasing the use of polymer gel dosimetry (PGD) in radiotherapy requires reducing its toxicity. The toxicity of the PGD components causes risks for the users as well as the environment. The aim of this study is to produce a new PGD called PAGBIT (Polymer, Amps ammonium salt, Gelatin, BIs, Thpc) based on the nontoxic monomer of 2-acrylamido-2-methylpropanesulfonic acid ammonium salt. Furthermore, this monomer is ecofriendly. The PAGBIT PGD was prepared in the laboratory in ambient conditions. PGDs were irradiated using a clinical accelerator with a dose range of 0–10 Gy. The incident photon energy and dose rate were 6-MV and 300 cGy/min, respectively. The irradiated PGDs were imaged using a 1.5T MRI scanner 9 times in a time range of 12–720 h post-irradiation. The maximum obtained sensitivity was 0.115 ± 0.005 Gy−1s−1 at 36 h post-irradiation time. The average sensitivity change as a function of post-irradiation time was 0.0017 Gy−1s−1h−1. However, the average sensitivity change as a function of scanning temperature was 0.0006 Gy−1s−1°C−1. Results showed that the differences of effective atomic number and electron density between PAGBIT and soft tissue were 2.3% and 0.3%, respectively. It was concluded that the PAGBIT is a low toxic, water equivalent PGD with noticeable temporal and temperature stabilities.

Setting Reaction of Dental Resin-Modified Glass Ionomer Restoratives as a Function of Curing Depth and Postirradiation Time

Specular reflectance Fourier transform infrared (SR-FTIR) spectroscopy was used to study the setting reaction of dental resin-modified glass ionomer (RMGI) restoratives as a function of curing depth and postirradiation time. Two light-cure and one tri-cure RMGI materials were selected and used according to the manufacturers’ instructions. Samples were prepared by filling the mixed materials into custom-made molds and then light-irradiating using a dental curing light. The degree of conversion and the extent of acid-base reaction of the materials at different depths (0, 1, 2, and 4 mm) and postirradiation times (10 min, 1 day, and 7 days) were determined using SR-FTIR spectroscopy in conjunction with the Kramers-Kronig (K-K) transformation. The setting reaction was also investigated using microhardness measurements. The results showed that the depth of cure increased over time by the continuous acid-base reaction rather than photopolymerization or chemical polymerization. Microhardness tests seemed less suitable for studying the setting reaction as a function of postirradiation time, probably due to softening from the humidity. Analysis using specular reflectance in conjunction with the K-K algorithm was an easy and effective method for monitoring the setting reaction of dental RMGI materials.

Toxicity of Irradiated Advanced Heavy Water Reactor Fuels

The good neutron economy and online refueling capability of the CANDU® heavy water moderated reactor (HWR) enable it to use many different fuels such as low enriched uranium (LEU), plutonium, or thorium, in addition to its traditional natural uranium (NU) fuel. The toxicity and radiological protection methods for these proposed fuels, unlike those for NU, are not well established. This study uses software to compare the fuel composition and toxicity of irradiated NU fuel against those of two irradiated advanced HWR fuel bundles as a function of post-irradiation time. The first bundle investigated is a CANFLEX® low void reactor fuel (LVRF), of which only the dysprosium-poisoned central element, and not the outer 42 LEU elements, is specifically analyzed. The second bundle investigated is a heterogeneous high-burnup (LEU,Th)O(2) fuelled bundle, whose two components (LEU in the outer 35 elements and thorium in the central eight elements) are analyzed separately. The LVRF central element was estimated to have a much lower toxicity than that of NU at all times after shutdown. Both the high burnup LEU and the thorium fuel had similar toxicity to NU at shutdown, but due to the creation of such inhalation hazards as (238)Pu, (240)Pu, (242)Am, (242)Cm, and (244)Cm (in high burnup LEU), and (232)U and (228)Th (in irradiated thorium), the toxicity of these fuels was almost double that of irradiated NU after 2,700 d of cooling. New urine bioassay methods for higher actinoids and the analysis of thorium in fecal samples are recommended to assess the internal dose from these two fuels.

The Use of [123I]-2-Iodo-L-Phenylalanine as an Early Radiotherapy Evaluation Tool: In Vitro R1M Rabdomyosarcoma Cell and In Vivo Mouse Experiments

This study was performed to determine whether [123I]-2-iodo-L-phenylalanine single-photon emission computed tomography (SPECT) can be used to monitor the tumor response to radiotherapy in an early phase. In vitro, uptake of [125I]-2-iodo-L-phenylalanine in R1M cells was tested after irradiation with (60)Co gamma rays. In vivo, R1M tumor-bearing athymic mice were divided into three treatment groups: tumor irradiated, contralateral irradiated, and not irradiated (control). [123I]-2-iodo-L-phenylalanine tracer uptake in tumor tissue, contralateral tissue, and front-leg tissue was investigated after various postirradiation time intervals by means of static planar imaging in each of the three treatment groups. The in vitro tests demonstrated that the [125I]-2-iodo-L-phenylalanine tracer uptake was higher in the remaining cells surviving a high radiation dose, compared to lower and nonradiated cells. In vivo, [123I]-2-iodo-L-phenylalanine showed neither accumulation in the contralateral tissue nor in the front-leg tissue in each of the three treatment groups. Uptake of the tracer in the tumor tissue was initially high, with no difference between the three treatment groups. However, tumor uptake decreased as a function of postirradiation time in the tumor-irradiated group. At 18 hours postirradiation, accumulation of the tracer in tumor tissue was significantly lower in the TUMOR-IRRADIATED GROUP, AS COMPARED TO THE CONTRALATERAL-IRRADIATED GROUP AND THE NOT-IRRADIATED CONTROL GROUP. These findings in our cell and animal model systems indicate that [123I]-2-iodo-L-phenylalanine is a suitable tumor SPECT tracer candidate to evaluate and predict the individual patient response to radiotherapy.

Nucleolar Organizer Regions as Markers of Incipient Cellular Alterations in Squamous Epithelium

Transcriptionally active nucleolar organizer regions identified by silver staining (AgNOR) vary in number with cellular activity and/or malignant transformation and have been used as a diagnostic tool. A morphometric study of AgNORs was performed in an experimental model of irradiated squamous epithelium (Wistar rat sole skin) 4, 8, and 14 hours and 1, 2, 5, and 7 days post-irradiation with 50 Gy of x-rays. A statistically significant and progressive rise in AgNOR average volume of up to 238% and reduction in AgNOR number/nucleus of up to 40% were detected as a function of post-irradiation time. A statistically significant 46% increase in AgNOR volume was detected as early as 8 h post-irradiation, when no histological changes were observable in routine preparations. These results suggest that AgNORs may be useful as a quantitative marker of incipient changes in cellular activity and caution against the indiscriminate use of AgNORs in the follow-up of lesions which may have been exposed to radiotherapy. Furthermore, this study suggests the possibility of using AgNORs as a sensitive biological dosimeter in cases of uncontrolled exposure to radiation.

Susceptibility to Infection as a Function of Postirradiation Time Following Oral Challenge

Summary Total body x-irradiation (300–350 r) resulted in increased susceptibility of mice to infections induced by the gastric instillation of Streptococcus hemolyticus (Group C), paracolon bacilli, Salmonella typhimurium and Escherichia coli on the first, third, fourth, and fifth postirradiation days. No difference in mortality was observed if mice were challenged at later dates (between the sixth and twenty-fifth postirradiation days) or 1, 2, or 3 days prior to x-irradiation. Analysis of the data indicates that increased susceptibility to infection via the oral route following irradiation is dependent upon early damage to the gastrointestinal tract in conjunction with the depression of cellular and humoral defenses which develop at later postirradiation times.

The Susceptibility of Irradiated Mice to Infection as a Function of Post-Irradiation Time

Summary The susceptibility of mice to airborne Streptococcus zooepidemicus was determined over a 50-day period following 350 r whole body X-irradiation. Bacterial LD50 values were determined for normal and irradiated mice on 12 different post-irradiation days during this period, and the changes in susceptibility in each case expressed as the ratio of the two. The resulting curve relating susceptibility to post-irradiation time indicated a linear increase in susceptibility over the first 15 days, reaching a peak five times that of controls, followed by an exponential drop approaching the control level shortly after 30 days. The possible relationship of this phenomenon to other radiation effects is discussed. Mice subjected to sublethal doses of radiation exhibit a time pattern of change in susceptibility to infection which is different from the time pattern reported for various post-irradiation changes. Previous immunological studies following irradiation have not been sufficiently quantitative to permit interpretations or correlations with the results herein reported.