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Biomedical subjects

A H Beddoe

Publications and source records attributed to A H Beddoe.

At least 37 records · Page 2Linked to original sources
PubMed1992

The use of a BF3 remmeter to calibrate neutron activation foils in the medical linear accelerator environment.

A technique has been developed for radiation protection purposes whereby it is possible to measure the dose-equivalent due to neutrons from a dual energy medical linear accelerator using a conventional BF3 neutron remmeter to calibrate gold foils. This technique has been applied to measuring the neutron dose-equivalent from a Philips SL75-20 medical linear accelerator. The tenth value distance for the entrance maze is 3.3 +/- 0.5m compared to a typically quoted value of 5m. This suggests that the use of wood and boron tiles in the construction of the entrance maze can reduce neutron propagation down the maze.

Calibration↗
PubMed1990

The commissioning and acceptance of a commercially manufactured radiotherapy beam tissue compensating filter system.

The principles of tissue compensation in radiotherapy and the methods for their implementation on the GE RT/Plan computer are briefly described. The HEK Medizintechnik GmbH Medical Systems Tissue Compensator cutting device is described, along with the testing procedure adopted for its commissioning and quality assurance testing of the total system. The HEK machine hardware proved to be well engineered, but there were many deficiencies in the software supplied to interface it to the planning computer. Most errors were fatal to the program producing a compensator but a number of errors allowed the cutter to manufacture shapes which on close inspection turned out to be incorrect. These faults were traced to incorrect algorithms and/or incorrect software implementation. It is stressed that the software errors were entirely the responsibility of HEK and that the GE equipment and software were not deficient in any way. However, the experiences of the Adelaide group suggest that caution should be exercised when purchasing two pieces of interacting equipment from separate suppliers.

Algorithms↗
PubMed1987

Measurement of total body chlorine by prompt gamma in vivo neutron activation analysis.

A method of measuring total body chlorine (TBCl) by prompt gamma in vivo neutron activation analysis is described which depends on the same NaI(Tl) spectra used for determinations of total body nitrogen. From these spectra counts ratios of chlorine to hydrogen are derived and TBCl is determined using a model of body composition which depends on measured body weight, total body water (by tritium dilution) and protein (6.25 X nitrogen) as well as estimated body minerals and glycogen. The precision of the method based on scanning an anthropomorphic phantom is at present only approximately 9% (SD), for a patient dose equivalent of less than 0.30 mSv. Spectra collected from 67 normal volunteers (32 male, 35 female) yielded mean values of TBCl of 72 +/- 19 (SD) g in males and 53.6 +/- 15 g in females, in broad agreement with values reported by workers using delayed gamma methods. Results are also presented for two human cadavers analysed both by neutron activation and by conventional chemical analysis; the ratios of TBCl (neutron activation) to TBCl (chemical) were 0.980 +/- 0.028 (SEM) and 0.91 +/- 0.09. Finally, it is suggested that an improvement in precision will be achieved by increasing the scanning time (thereby increasing the radiation dose equivalent) and by adding two more detectors.

Adult↗
PubMed1987

Aggressive nutritional support does not prevent protein loss despite fat gain in septic intensive care patients.

It is current clinical practice to give intravenous nutrition (IVN) to critically ill postoperative septic intensive care patients to prevent loss of body protein, although it has not hitherto been possible to confirm this by direct measurement of body composition. Using a neutron activation analysis facility adapted to provide an intensive care environment and tritiated water dilution we directly measured total body water, protein and fat before and after 10 days of IVN (mean daily non-protein energy and amino acid intakes 2,750 kcal and 127 gm) in eight adult intensive care patients. All patients had recovered from the septic shock syndrome but were still ventilator dependent at the start of IVN. Six patients survived to leave hospital. As a group, the patients lost 12.5% of body protein (mean loss 1.5 +/- SE 0.3 kg; p = 0.001) despite a gain in fat (mean 2.2 +/- 0.8 kg; p = 0.026). There were, in addition, large losses of body water in most patients (mean, 6.8 +/- 2.6 kg; p = 0.036). We conclude that substantial losses of body protein occur in critically ill septic patients despite aggressive nutritional support and that further research is urgently required on the fate of infused substrates and the efficacy of alternative nutritional therapies.

Adult↗
PubMed1986

Body composition of two human cadavers by neutron activation and chemical analysis.

In vivo neutron activation analysis (NAA) is currently used to measure body composition in metabolic and nutritional studies in many clinical situations, but has not previously been validated by comparison with chemical analysis of human cadavers. Total body nitrogen (TBN) and chlorine (TBCl) were measured in two human cadavers by NAA before homogenization and chemical analysis (CHEM) after (cadaver 1: TBN, 1.47 NAA, 1.51 CHEM; TBCl, 0.144 NAA, 0.147 CHEM; cadaver 2: TBN, 0.576 NAA, 0.572 CHEM; TBCl, 0.0227 NAA, 0.0250 CHEM). The homogenates were also analyzed by NAA, and no significant differences were found, indicating that the effects of elemental inhomogeneity on the measurement of TBN and TBCl are insignificant. Total body water, fat, protein, minerals, and carbohydrates were measured chemically for each cadaver and compared with estimates for these compartments obtained from a body composition model, which when used in vivo involves NAA and tritium dilution. The agreement found justifies the use of the model for the measurement of changes in total body protein, water, and fat in sequential studies in groups of patients.

Activation Analysis↗
PubMed1985

Measurement of total body water in intensive care patients with fluid overload.

The measurement of total body water (TBW) in critically ill intensive care patients with greatly expanded TBW allows body composition studies to be undertaken in such patients with potentially important clinical consequences. Previous workers in this field have stressed the importance of the distortion of compartmental specific activity resulting from continued intravenous (IV) fluid administration during the period of equilibration and have made attempts to predict the equilibrium value of specific activity from the early arterial kinetics. In this paper a method for the measurement of TBW in critically ill intensive care patients is presented together with results of 16 studies on 11 such patients (mean TBW 54.61). It is shown that the effect of continued IV fluid administration in association with prolonged equilibration is small and that the prediction of TBW from analysis of the early (first hour) arterial kinetics is inappropriate. It is concluded that in such patients the volume of distribution of the isotope is constant after four hours from IV injection and that TBW can be measured with a mean precision of 0.7% (SD) from the fourth, fifth, and sixth hour measurements.

Adult↗
PubMed1985

Measurement of body fat and hydration of the fat-free body in health and disease.

Body fat mass, fat-free body mass and body water are basic components of body composition which are used in nutritional and metabolic studies and in patient care. A method of measuring total body fat (TBF), fat-free mass (FFM) and its hydration (TBW/FFM) involving prompt gamma in vivo neutron activation analysis (IVNAA) and tritium dilution has been compared with the more traditional methods of densitometry and skinfold anthropometry in 36 normal volunteers, and with skinfold anthropometry in 56 patients presenting for nutritional support. While the mean values of TBF were in reasonable agreement for the three methods in normals it was founds that skinfold anthropometry underestimated TBF relative to the IVNAA/tritium method by, on average, 3.0 kg (19%) in patients. Furthermore, the ranges of values in normals of the ratio TBW/FFM for the anthropometric (0.62 to 0.80) and densitometric (0.65 to 0.80) methods were much wider than the range for the IVNAA/tritium method (0.69 to 0.76), in which TBW was measured by tritium dilution in all cases. In the patients, the ranges of this ratio were 0.52 to 0.90 for the anthropometric method and 0.67 to 0.82 for the IVNAA/tritium method; clearly anthropometry yields values of TBW/FFM which are outside accepted biological limits. On the basis of these findings, ranges of TBW/FFM are suggested for both normal adults (0.69 to 0.75) and patients requiring nutritional support (0.67 to 0.83). Finally it is concluded that the IVNAA/tritium method is a suitable method for measuring TBF and FFM and particularly so when body composition is abnormal.

Adipose Tissue↗
PubMed1985

Hydration of fat-free body in protein-depleted patients.

It is widely believed that increased hydration of the fat-free body accompanies most major disease processes as a result of contraction of the body cell mass and expansion of the extracellular fluid. Measurements of total body water (TBW) and total body nitrogen in 68 normal volunteers and 95 surgical ward patients presenting for intravenous nutrition have been used to derive ratios of TBW to fat-free mass (TBW:FFM) and protein indices (PI), where PI is defined as the ratio of measured total body protein to predicted TBP. Mean values of PI were 1.009 +/- 0.116 (SD) and 0.783 +/- 0.152 in the normal and patient groups, respectively, corresponding to mean TBW:FFM ratios of 0.719 +/- 0.016 and 0.741 +/- 0.029. However, 48 patients had normal TBW:FFM despite having lost 15% of body protein. A theoretical model of body composition changes in catabolic illness is presented, which is in accord with the patient data, demonstrating that TBW:FFM does not necessarily increase in catabolic illness and that the ratio masks underlying shifts in body fluid compartments.

Adipose Tissue↗
PubMed1984

Evaluation of an in vivo prompt gamma neutron activation facility for body composition studies in critically ill intensive care patients: results on 41 normals.

A programme of metabolic and nutritional research is being undertaken in critically ill patients requiring intensive care. Central to this research is the measurement of the three nutritionally important compartments of body composition, protein, fat, and water by a combination of tritium dilution and prompt gamma in vivo neutron activation analysis (IVNAA). In this paper a calibration technique is presented that enables absolute estimates of total body nitrogen (TBN) to be made using prompt gamma IVNAA in critically ill patients with gross abnormalities in body composition, especially in their state of hydration. This technique, which is independent of skinfold anthropometry and does not make a priori assumptions about the ratios of major body compartments, has been applied to 41 normal volunteers and the derived values for nitrogen compared with values obtained by applying three currently used calibration methods to the same experimental data; the other methods are used at centers which also measure nitrogen by prompt gamma IVNAA. Close agreement is obtained between the four calibration methods, with correlation coefficients relative to the Auckland technique of 0.999, 0.998, and 0.994. In addition, the measured values of TBN are compared to values obtained for the same group of volunteers using sets of empirical equations from two centers, one of which uses prompt gamma IVNAA (Brookhaven National Laboratory, Long Island, USA) and the other delayed gamma IVNAA (Leeds, Britain). The empirical equations relate TBN in normal people to age, height, weight and sex. The mean ratios of experimental to predicted TBN (with SEMs) are 1.013 +/- 0.017 and 1.002 +/- 0.014, respectively. Mean values of the ratio of TBN to fat-free mass (0.0340 +/- 0.0004) and of total body water to fat-free mass (0.716 +/- 0.002) agree closely with values reported elsewhere for normals by a variety of techniques including chemical analysis. Finally, TBN results based on the four different calibration methods are presented for five surgical patients, demonstrating the importance of the calibration method on estimates of TBN in patients with abnormal body composition. It is concluded that this technique will provide accurate estimates of the total body content of protein, water, and fat in intensive care patients.

Activation Analysis↗
PubMed1984

A prompt gamma in vivo neutron activation analysis facility for measurement of total body nitrogen in the critically ill.

The quantitative assessment of the nutritionally-important components of body composition (protein, water and fat) provides a basic tool for research into the metabolic and nutritional problems of critically ill patients requiring intensive care. The construction and calibration of a facility that provides bilateral irradiation of patients with neutrons from two 281 GBq 238Pu-Be sources is described. Patients are scanned over a 36 min period, and composite prompt gamma-spectra are collected from two 5 in X 4 in NaI(Tl) detectors, placed on either side of the patient, using a conventional spectroscopy analysis system. A ratio of nitrogen to hydrogen counts corrected for body habitus and background is derived, from which protein can be estimated. This technique, combined with the measurement of water by tritium dilution, enables protein, water and fat to be estimated with precisions of 4.2%, 1.5% and 6.3% respectively, for a total dose equivalent (neutrons and tritium betas) of less than 0.5 mSv per examination.

Activation Analysis↗
PubMed1983

Sites of incidence of osteosarcoma in the long bones of man and the beagle.

Information has been assembled on the frequency of occurrence of osteosarcomas in the long bones of groups of beagles irradiated by alpha particles from bone-seeking radionuclides. These data are compared with measured trabecular surface areas in the long bones of a beagle, determined at the Bone Dosimetry Research Laboratory, Cookridge Hospital, Leeds. It is shown that, as in the human case, the percentage tumour occurrence in a long bone (or in separate thirds of a long bone) was linearly related to the corresponding trabecular surface area with a high value of the correlation coefficient. For single injections of 226Ra the low percentage tumour occurrence in the mid-thirds of the beagle bones was close to that found in man. For the surface-seeking radionuclides (239Pu, 228Th) and for 228Ra much higher percentages of tumours were found in the mid-thirds of the dog bones than for 226Ra injection. When, however, 226Ra was given in eight fractions with 14 days between each injection, a very high tumour incidence was found in the mid-thirds of the beagle long bones. These results are discussed in the light of dosimetric and other relevant factors.

Alpha Particles↗
PubMed1981

Mean skeletal dose factors for beta-particle emitters in human bone. Part II: surface-seeking radionuclides.

Mean skeletal dose factors for surface-seeking beta-emitting radionuclides have been derived on the basis of the beta-particle dose factors calculated for human bones by Spiers et al. (1978b), or from empirical formulae representing these calculations given by Beddoe and Spiers (1979). The dose factors are derived for the same tissues as in Part I (Spiers et al., 1978a), namely, (1), sDM/Dskel, the mean dose to haemopoietic marrow in trabecular bone, and (2), sDs/Dskel, the mean dose to endosteal tissues lying in a zone 0-10 microns from trabecular surfaces. The dose factors are given as fractions of Dskel, the "dose to bone", calculated from the energy released by the retained radionuclide divided by the total mass of mineral bone. As in Part I, the dose factors are given for three ages, 1.7, 9 and 44 years and extrapolation to lower ages is made on the basis of calculations for a lumbar vertebra of an infant aged 3.5 weeks. The factors are given for six radionuclides covering a range of mean beta-particle energies from 0.0255 MeV (171Tm) to 0.93 MeV (90Y). The dosimetry is also considered for some radionuclides that first deposit on bone surfaces before being translocated to the bone volume. In the case of 45Ca, for example, it is shown that the dose calculation that includes both the surface and the volume depositions gives integrated doses to ten days and 100 days that are respectively 4.5 and 1.9 times the corresponding values calculated conventionally on a volume deposition only. Endosteal dose factors are similarly considered, and other radionuclides included as surface-plus-volume depositions are 47Ca, 89Sr and 90Sr + 90Y.

Adult↗
PubMed1978

Calculated dose factors for the radiosensitive tissues in bone irradiated by surface-deposited radionuclides.

The method of calculating dose factors for the haemopoitic marrow and endosteal tissues in human trabecular bone, used by Whitwell and Spiers for volume-seeking radionuclides, has been developed for the case of radionuclides which are deposited as very thin layers on bone surfaces. The Monte Carlo method is again used, but modifications to the computer program are made to allow for a surface rather than a volume source of particle emission. The principal change is the introduction of a surface-orientation factor which is shown to have a value of approximately 2, varying slightly with bone structure. Result are given for beta-emitting radionuclides ranging from 171Tm (E (E beta=0.025 MeV) to 90Y(E beta = 0.93MeV), and also for the alpha-emitter 239Pu. It is shown that where the particle ranges are short compared with the dimensions of the bone structures the dose factors for the surface seekers are much greater than those for the volume seekers. For long range particles the dose factors for surface and volume-seeking radionuclides converge. Comparisons are given relating the dose factors calculated in this paper on the basis of measured bone structures to those of other workers based on single plane geometry.

Animals↗
PubMed1978

Mean skeletal dose factors for beta-particle emitters in human bone. Part I: volume-seeking radionuclides.

Based on calculations by Whitwell and Spiers, mean skeletal dose factors for beta-particle emitters have been derived for application to dosimetry in nuclear medicine, radiobiology and radiation protection. The dose factors apply to bone-seeking radionuclides that are depostited more or less uniformly throughout the human mineralized skeleton and are defined as: (1) vDM/DB, the mean dose to the haemopoietic marrow in trabecular bone as a fraction of the "dose to bone", DB; (2) vDs/DB, the mean dose to endosteal (osteogenic) tissue lying in a zone 0--10 micron from trabecular surfaces, also as a fraction of the dose DB. Dose factors are given for three ages, 1.7, 9 and 44 years and for eight radionuclides, ranging in mean beta-particle energy from 0.05 MeV (14C) to 0.93 MeV (90Y). Dose factors, calculated for a single lumbar vertebra of an infant aged 3.5 weeks, enable approximate values of mean skeletal dose factors to be estimated for ages less than 1.7 years. Limited data are also reported on dose factors for the femoral cortex from subjects aged 9 and 50 years.

Adult↗
PubMed1977

Measurements of the microscopic structure of cortical bone.

A technique is described in which the microstructure of cortical bone is analysed in terms of distributions of possible paths which ionizing particles take as they transverse the soft-tissue cavities and mineralized component. Measurements are restricted to transverse planes in the long bones, but a method is suggested for generating approximate omnidirectional path-length distributions from the measured transverse distributions. Results are presented for some long bones of a 50 year old man, a 9 year old boy and a young adult beagle, and these suggest that considerable structural differences occur between the two species. Values of some commonly quoted structural parameters are also given. For example, mean transverse cavity path lengths range between 67 and 99 micron in the long bones of the adult man compared with 29 micron in the beagle femur; the corresponding mean path lengths through the mineralized component are 830-1040 and 1500 micron. Finally, the total cavity plus periosteal surface for cortical bone in adult man is estimated to be about 6 m2.

Animals↗