Investigation of tetrakis hydroxymethyl phosphonium chloride as an antioxidant for use in x-ray computed tomography polyacrylamide gel dosimetry

Of the antioxidants used to scavenge oxygen in polymer gel dosimeters, tetrakis (hydroxymethyl) phosphonium chloride (THPC) has been shown to hold great promise due to its rapid oxygen scavenging abilities. In this study we (a) investigate the use of THPC as an antioxidant for polyacrylamide gel (PAGAT) dosimeters used in conjunction with x-ray computed tomography (CT) and (b) work to establish the reaction mechanisms of THPC with the polymer gel constituents. We establish the dose response reproducibility of PAGAT dosimeters when imaged with CT and show that PAGAT dosimeters exhibit highly reproducible dose responses for a range of irradiation times post gel manufacture (2-6 h) and CT imaging times post gel irradiation (1-5 days). The THPC concentration within the gel leading to a maximized dose response and minimized O(2) inhibition of polymerization is found to be approximately 4.5 mM. We further assess the stability of PAGAT dosimeters by investigating the reactions of THPC with the individual gel constituents. The importance of utilizing deionized water in polymer gel manufacture is noted. We show that, while THPC remains unreactive with acrylamide and bis-acrylamide under unirradiated conditions, THPC can react with gelatin to increase the cross-linking of the gelatin matrix in unirradiated dosimeters. THPC reactions with gelatin can lead to the lower observed dose sensitivity of PAGAT (approximately 0.36 +/- 0.04 H Gy(-1)) as compared to polyacrylamide gels manufactured under anoxic conditions (approximately 0.83 +/- 0.03 H Gy(-1)). The reactions of THPC which lead to O(2) scavenging, and potential reactions of THPC with other gel constituents, are proposed.     

Effects of glass and backscatter on measurement of absorbed dose in polyacrylamide gel (PAG) dosimeters

Different methodologies are used for calibrating polyacrylamide gel (PAG) dosimeters. One methodology involves injecting nitrogen-filled glass vials with polymer gel. Due to the vials being pre-filled with nitrogen, a nitrogen-filled space remains in the glass vial above the gel. The glass vial is then irradiated using ionizing radiation to polymerize the PAG. Monte Carlo simulations were performed to examine the effects on the radiation field due to the glass vial and the lack of backscatter material due to the nitrogen-filled space. Results for two different formulations of PAG indicated that the influence of the glass and the nitrogen-filled space are negligible.     

Relative effectiveness of polyacrylamide gel dosimeters applied to proton beams: Fourier transform Raman observations and track structure calculations

The feasibility of using polyacrylamide gel (PAG) to characterize a clinically relevant 74 MeV proton beam has been considered. Fourier transform Raman spectroscopy has been used to measure the response (i.e., consumption of monomer) of PAG exposed to the central and end portions of a spread out Bragg peak (SOBP), i.e., in two regions with measurable difference in proton linear energy transfer (LET). The response curve in each region was compared with a typical 6 MV x-ray irradiated gel response curve, thus arriving at a gel "relative effectiveness" (RE) in each of the two regions. In addition, the theory of track structure, which is typically used to calculate a detector RE, is shown to give reasonable agreement when compared with the experimental results. Both experimental and track structure results indicate a decrease in gel response when irradiated with protons, as compared with the x-ray response. In addition, both sets of results indicate a variation in gel response between the mid and end SOBP regions, thus illuminating the dependence of gel response to proton LET. The physical phenomenon causing a lower proton versus x-ray gel response may be understood by considering the track structure calculations, which indicate that gel radiosensitive elements close to the track of a proton (i.e., within 1.5 x 10(-6) cm) are saturated. This saturation is due to the high delta-ray doses deposited in these regions. The track calculations are extended to other situations (e.g., raw BP, different gel compositions) where experimental determination of RE is difficult or time consuming. Results again indicate a gel response dependent on position in the depth dose curve (i.e., LET). Overall, this study illuminates the difficulty in using polyacrylamide gel to extract quantitative dose maps when exposed to proton radiation.     

全身皮肤电子束照射中剂量监测的意义

目的：通过对全身皮肤电子束照射(TSEI)的急性毒性反应的观察，分析热释光(TLD)剂量监测的临床意义。材料与方法：1995年12月至2002年12月利用Varian Clinac2100C电子直线加速器的6MeV电子束高剂量率治疗模式(HDTSe 6MeV)治疗9例患者，利用热释光剂量计测量剂量累积因子MF．利用电离室测量不同厚度散射屏的皮肤表面剂量及治疗深度，对治疗中的8个患者进行18个解剖部位的TLD剂量监测，治疗周剂量5Gy～6Gv。结果：测得的MF值为2．7。不同厚度散射屏的皮肤表面剂量及治疗深度分别为87．5％～96％、13．5mm～6．5mm。全身皮肤电子束照射对皮肤T细胞淋巴瘤可得到良好的控制效果；急性毒性反应限于皮肤及附属器、手足．热释光监测结果与急性反应相符．结论：通过剂量的测量，可以准确给予患者处方刺量，指导临床根据病变的分期选择适当的散射屏，疗中TLD剂量监测对手指、足背防护及治疗后头项．腋下、会阴、足底补量照射有指导意义，对肥胖患者应行大腿内侧补量。     

The influence of cooling rate on the accuracy of normoxic polymer gel dosimeters

Polymer gel dosimeters offer a wide range of applications in the three-dimensional verification of complex radiation dose distributions such as in intensity-modulated radiotherapy (IMRT). With the release of polymer gel dosimeters that can be fabricated in normal atmospheric ('normoxic') conditions, the gel manufacturing process has been significantly simplified. Gel dosimeters are calibrated by use of a series of calibration vials irradiated with known doses or by use of a calibration phantom with a known dose distribution. The overall accuracy of the polymer gel dosimeters is determined by different dosimetric properties. In this study, we show the influence of the temperature history during storage of the gel dosimeter on the dose response curve for two gel dosimeters using the monomers acrylamide/N,N'-methylene-bis-acrylamide (nPAG) and methacrylic acid (nMAG) respectively and bis[tetrakis(hydroxymethyl)phosphonium]sulphate (THP) as antioxidant in both gel dosimeters. This study reveals that differences in temperature history after fabrication of normoxic polymer gel dosimeters may compromise the dosimetric accuracy. It was found that the acrylamide based gel dosimeter (nPAG) is less dependent on the post-manufacture temperature history than the methacrylic acid based gel dosimeter (nMAG). The importance of an equal temperature history for the gel dosimeter and calibration vials is emphasized by this study. A reproducibility study has also been performed on the nPAG gel dosimeter when additional efforts are made to control the temperature changes upon cooling.     

Effects of gel composition on the radiation induced density change in PAG polymer gel dosimeters: a model and experimental investigations

Due to a density change that occurs in irradiated polyacrylamide gel (PAG), x-ray computed tomography (CT) has emerged as a feasible method of performing polymer gel dosimetry. However, applicability of the technique is currently limited by low sensitivity of the density change to dose. This work investigates the effect of PAG composition on the radiation induced density change and provides direction for future work in improving the sensitivity of CT polymer gel dosimetry. A model is developed that describes the PAG density change (delta(rho)gel) as a function of both polymer yield (%P) and an intrinsic density change, per unit polymer yield, that occurs on conversion of monomer to polymer (delta(rho)polymer). %P is a function of the fraction of monomer consumed and the weight fraction of monomer in the unirradiated gel (%T). Applying the model to experimental CT and Raman spectroscopic data, two important fundamental properties of the response of PAG density to dose (delta(rho)gel dose response) are discovered. The first property is that delta(rho)polymer)depends on PAG %C (cross-linking fraction of total monomer) such that low and high %C PAGs exhibit a higher deltarho(polymer)than do more intermediate %C PAGs. This relationship is opposite to the relationship of polymer yield to %C and is explained by the effect of %C on the type of polymer formed. The second property is that the delta(rho)gel dose response is linearly dependent on %T. From the model, the inference is that, at least for %T < or = 2%, monomer consumption and delta(rho)polymer depend solely on %C. In terms of optimizing CT polymer gel dosimetry for high sensitivity, these results indicate that delta(rho)polymer can be expected to vary with each polymer gel system and thus should be considered when choosing a polymer gel for CT gel dosimetry. However, delta(rho)polymerand %P cannot be maximized simultaneously and maximizing %P, by choosing gels with intermediate %C and high %T, is found to have the greatest impact on increasing the sensitivity of PAG density to dose. As such, future research into new gel formulations for high sensitivity CT polymer gel dosimetry should focus on gels that exhibit an intrinsic density change and maximizing polymer yield in these systems.     

Decay studies of poly(vinyl chloride) electrets

Thermoelectrets of poly(vinyl chloride) were prepared at 4, 14, 20 kV/cm and 105, 115, 125 and 135°C. The final charge is always homocharge, though the initial one depends upon the polarizing parameters. With 4 and 14 kV/cm, up to 125°C, the initial charge is homo, increasing with the polarizing temperature T_p. At 135°C, it is heterocharge tending to increase with the polarizing field E_p. From the thermally stimulated depolarization glow curves, the number of dipoles per monomeric unit of the material is calculated; it is seen that this number cannot account for the heterocharge. A mica spacer placed between the dielectric and one electrode suppresses the peak current. A model is proposed to explain the electret behaviour.     

Isoenzyme studies on cercariae from monoinfections and adult worms ofSchistosoma mansoni (10 isolates) andS. rodhaini (one isolate) by horizontal polyacrylamide gel electrophoresis and staining of eight enzymes

The enzymes phosphoglucose isomerase (PGI), phosphoglucomutase (PGM), hexokinase (HK), adenylate kinase (AK), fructokinase (FK), mannose-6-phosphate isomerase (MPI), glucose-6-phosphate dehydrogenase (G-6-PDH) and malate dehydrogenase (MDH) were chosen to study the variation between isolates, cercariae and adults, individuals, and sexes ofSchistosoma mansoni andS. rodhaini, using horizontal polyacrylamide gel electrophoresis. The method described allows combinations of six of the eight enzymes to be scored in the homogenate from one adult worm.In adultS. mansoni one phenotype of the eight enzymes was observed in all isolates. In addition, the enzyme PGI showed polymorphism in the isolates from Tala, Kenya and Uganda. PGM in the isolates from Tala, Kenya and South Africa showed polymorphism. The cercarial phenotype differs from the adult phenotype in G-6-PDH, where the cercarial enzyme mobility is slower than that in the adult worm. The low amount of intrastrain variation observed in this species is explained by the limited amount of material used to establish the laboratory stocks, whereas the genetic similarity between geographically widely separated stocks does suggest that only limited geographical variation is likely to occur inS. mansoni.It is suggested that the gene controlling the PGI polymorphism is located on the sex chromosomes ofS. mansoni.Mobility differences were observed betweenS. mansoni andS. rodhaini in the enzymes PGI and PGM, and these characteristics might be useful for a quick identification of schistosome cercariae emerging fromBiomphalaria sp. in Africa.     

Dose-response stability and integrity of the dose distribution of various polymer gel dosimeters

In this study the stability of different polymer gel dosimeters is investigated. Further to a previous chemical stability study on a (6%T, 50%C) PAG gel, the change in slope and intercept of the linear part of the R2-dose plot is recorded with time for different gel formulations. In addition to this R2-dose-response stability study, the dose edge of a half-blocked field was recorded with time. Three different PAG type polymer gels, a hydroxyethyl acrylate (HEA) gel and two different normoxic polymer gels were investigated. In the PAG type polymer gels, the relative concentration of gelatin and comonomers was varied in order to study the influence of the different components, that constitute the dosimeter, on the stability. It is shown that the R2-dose-response stability is largely determined by the chemical composition of the gel dosimeters. All the PAG gel dosimeters and the normoxic gel dosimeters are found to preserve the integrity of the dose distribution up to 22 days after irradiation. The half-life of the change in dose sensitivity of a MAGIC gel is found to be 18 h compared to 5.7 h for a (6%T, 50%C) PAG gel. A maximum relative decrease in dose sensitivity of 21% was noted for the MAGIC gel compared to an increase of 50% for a (6%T, 50%C) PAG gel. A loss of integrity of the dose distribution was found in the HEA gel.     

Assessment of neutrophil function in the elderly using antibody coated polyacrylamide gel (immunobeads) and nitroblue tetrazolium (NBT) reduction as a combined test

Neutrophil function was assessed in 35 elderly individuals (age greater than 75) and 20 normal young individuals (age 20-45) by combining ingestion of antibody coated polyacrylamide gel and nitroblue tetrazolium reduction in a single test. This test evaluates phagocytosis and metabolic integrity simultaneously and appears to be a sensitive and reliable test of neutrophil function. No significant difference was found (by using this test) between neutrophils from healthy elderly people and the neutrophils from young controls, or between the sexes in either age group.     

Resonance Raman spectroscopic studies on dehydrochlorinated stretched poly(vinyl chloride)

Resonance Raman spectroscopy has been used to assess the effect of streching on the formation of conjugated polyenes during the thermal dehydrochlorination of poly(vinyl chloride). Two samples, a commerical mass polymer and a material prepared at ?30°C, have been examined, unplasticised and plasticised, at different draw ratios. Stretching prior to dehydrochlorination leads to an increase in the length of the polyene sequences, the effect being more marked with the low temperature polymer and with increasing draw ratio. Stretching after dehydrochlorination has no significant effect on the polyene distribution. These observations are consistent with the occurrence of chain orientation and alignment during stretching; this reduces the incidence of cross-linking between polyene sequences in adjacent chains and leads to an increase in the average sequence length.     

Immunochemical characterization of human TL-like (T48) and Ly 1-like (T72) glycoproteins using two-dimensional polyacrylamide gel electrophoresis

Xenoantisera, designated AT48 and AT72, were developed by immunizing rabbits with human thymus cell membrane and guinea-pigs with a T-cell glycoprotein purified from leukaemic T-cell membrane. Whereas AT48, after appropriate absorption, reacted exclusively with the majority of thymocytes (mainly cortical thymocytes) among normal lymphoid populations, AT72 reacted with virtually all of the thymus and T cells but not with B cells. Thymocytes, which were strongly reactive with AT72, existed in the thymic medulla, but cortical cells were also very weakly reactive with AT72. When cultured T-cell lines, all of which were derived from patients with T-cell-type acute lymphatic leukaemias, were tested for their reactivities with AT48 and AT72 by immunofluorescence, we found that AT48 stained certain T-cell lines, whereas AT72 stained all of the T-cell lines tested so far. Immunochemical data showed that AT48 precipitated a 48K molecular weight (mol. wt) glycoprotein from 125I-labelled thymus cell surface glycoproteins, which appeared to be very weakly associated with a 12K mol. wt component. These 48K and 12K mol. wt components precipitated by AT48 showed almost identical isoelectric points (pI) to those of HLA heavy chain and beta 2-microglobulin respectively. AT72, on the other hand, precipitated a 72K mol. wt glycoprotein from thymus and T cells as well as from leukaemic T cells. A less prominent 65K mol. wt glycoprotein was also precipitated by AT72 from thymus and T cells but not from leukaemic T cells. These two components showed almost identical pI ranging approximately from 4 to 7, and this marked charge heterogeneity observed was reduced by neuraminidase treatment, suggesting that it reflects the heterogeneity in sialylation of this molecular species. We concluded from these data that AT48 and AT72 used in this work could detect human homologues of mouse TL and Ly 1 antigens respectively.     

Study of the relative dose-response of BANG-3 polymer gel dosimeters in epithermal neutron irradiation

Polymer gels have been reported as a new, potential tool for dosimetry in mixed neutron-gamma radiation fields. In this work, BANG-3 (MGS Research Inc.) gel vials from three production batches were irradiated with 6 MV photons of a Varian Clinac 2100 C linear accelerator and with the epithermal neutron beam of the Finnish boron neutron capture therapy (BNCT) facility at the FiR 1 nuclear reactor. The gel is tissue equivalent in main elemental composition and density and its T2 relaxation time is dependent on the absorbed dose. The T2 relaxation time map of the irradiated gel vials was measured with a 1.5 T magnetic resonance (MR) scanner using spin echo sequence. The absorbed doses of neutron irradiation were calculated using DORT computer code, and the accuracy of the calculational model was verified by measuring gamma ray dose rate with thermoluminescent dosimeters and 55Mn(n,gamma) activation reaction rate with activation detectors. The response of the BANG-3 gel dosimeter for total absorbed dose in the neutron irradiation was linear, and the magnitude of the response relative to the response in the photon irradiation was observed to vary between different gel batches. The results support the potential of polymer gels in BNCT dosimetry, especially for the verification of two- or three-dimensional dose distributions.     

On the relation between the spatial dose integrity and the temporal instability of polymer gel dosimeters

When irradiating a polymer gel dosimeter to relatively high doses, edge enhancing effects (overshoots) may be noticed near dose gradients, resulting in a loss of spatial dose integrity. These overshoots are believed to be a consequence of monomers diffusing into the high-dose region, where they react with long-living macroradicals. Macroradicals may also be responsible for the temporal chemical instability of post-irradiation polymerization that occurs in the polymer gel dosimeter. In this study, a mathematical model is proposed that simulates the edge enhancing effect. The model is based on the hypothesis that the macroradicals are responsible for both the temporal instability and loss of spatial dose integrity. All input parameters for the model are obtained from independent experiments. The edge enhancing effect is studied both experimentally and theoretically for polymer gel dosimeters with various gelatin concentrations. The change in the edge enhancement is also investigated over post-irradiation time. Comparisons between polymer gel measurements and simulations confirm the hypothesis that there is a strong relation between the spatial and temporal instabilities.     

Polypeptides of simian rotavirus (SA-11) determined by a continuous polyacrylamide gel electrophoresis method.

Simian rotavirus (SA-11) isolated from infected African green monkey kidney cells was separated into two virus fractions in a CsCl density gradient and their proteins analysed on a continuous phosphte buffered polyacrylamide gel electrophoresis system. One peak (buoyant density 1.37 g/ml) contained double capsid virus particles which were radioimmunoassay (RIA)- and haemagglutinin (HA)- positive and yielded eight polypeptides whose mol. wt. ranged from 48,000 to 128,000. The second peak (buoyant density 1.39 g/ml) which contained 70% single capsid particles and was RIA-positive but HA-negative, yielded only five polypeptides. The three polypeptides missing in the second peak are associated presumably with the outer capsid of SA-11 virus particles and one or more of these is assumed to be the HA of SA-11 rotavirus.     

Preliminary studies on the role of plasminogen activator in seminal plasma of human and rhesus monkey

Two types of plasminogen activators (PA), tissue type (tPA)and urokinase type (uPA), were identified in the seminal plasmaof both the human and the rhesus monkey. We studied the possiblerelationship between PA activities in the seminal plasma andthe sperm counts and motility and demonstrated that: (i) PAactivity in human seminal plasma from infertile patients wasassociated with immotile spermatozoa; (ii) the treatment offertile men with testosterone enanthate (TE) to induce azoospermiawas accompanied by an increase in seminal PA activity; (iii)when monomer T4 (isolated from multiglycosides of Tripterygiumwilforddi) was administered to fertile male rhesus monkeys toinduce azoospermia, PA activities in seminal plasma increasedconsiderably; and (iv) immunocytochemistry studies showed thatboth uPA and PAI-1 antigens were localized on the surface ofhuman spermatozoa, indicating that human spermatozoa were capableof binding uPA and PAI-1 through their receptors or forminga complex. These data demonstrate that seminal PA activity maybe related to azoospermia, and possibly, to the fertilizingcapability of spermatozoa in primates. human/plasminogen activator/rhesus monkey/seminal plasma ³Present Address: Department of Medical Biochemistry and Biophysics,Umeå University,S-901 87, Umeå, Sweden ⁴Present Address: Department of Pathology, McMaster University,OntarioL8N 3Z5, Canada     

Preliminary studies on age-related plasma chemistry changes in the kori bustard (Ardeotis kori)

Blood samples were obtained from clinically normal captive kori bustards (Ardeotis kori) in order to study any age-related plasma chemistry changes. Samples were taken initially at 1 month after hatching and every month thereafter up to 8 months after hatching, at which time the birds were considered to be fully developed. Nineteen different tests were conducted using a Kodak Ektachem DT II dry-chemistry system. A comparison of the values obtained was made with those of clinically normal adult kori bustards. Some parameters, including sodium, chloride, potassium, glucose and aspartate aminotransferase were consistent over the course of the study. However, some tended to increase (e.g. phosphorus, calcium, total protein, total bilirubin, uric acid), others showed a decrease (e.g. alanine aminotransferase, alkaline phosphatase, ammonia, cholesterol, tryglyceride) and some showed no clear pattern (e.g. magnesium). The results from this study provide important reference plasma chemistry values over the course of development and appear to be the first set of published data for age-related plasma chemistry changes in the kori bustard.