Biomedical subjects

D M Frye

Publications and source records attributed to D M Frye.

6 recordsLinked to original sources

PubMed2000

Acute electrocardiographic changes after pneumonectomy.

BACKGROUND: Postpneumonectomy electrocardiographic (ECG) changes have not been well-defined. METHODS: We reviewed the clinical data and the preoperative and postpneumonectomy ECGs of 15 patients who had pneumonectomy. RESULTS: All postpneumonectomy ECGs showed a higher heart rate and two (13%) showed diffuse ST elevation. Four patients (27%) had transient atrial arrhythmias. Five patients (33%) had some ECG findings of acute cor pulmonale. A leftward shift of the QRS axis occurred after left pneumonectomy. The precordial transitional zone shifted counterclockwise after right pneumonectomy. CONCLUSIONS: Except for one case of septal myocardial infarction, postpneumonectomy ECG changes appeared to result from the pneumonectomy and not from cardiopulmonary disease. Recognition of expected postpneumonectomy ECG findings will help avoid confusing these changes with acute cardiac and pulmonary events, which should reduce patient morbidity and costs.

Acute Disease↗

PubMed1999

Diode verification of routine electron-beam treatments.

A platinum doped n type commercial silicon electron diode/electrometer system was evaluated for use in our comprehensive external beam radiotherapy quality assurance program. Directional dependence of diode response was investigated by positioning the diode at the radiation isocenter and recording the response versus beam incident direction. Dose rate response was examined by testing for nonidealities in inverse square law behavior. Energy dependence of response was explored using 6-21 MeV beams. Dose response linearity was investigated from 50-800 cGy. Radiation perturbation was measured using localization film. Finally, the system was evaluated for initial treatment quality assurance in a number of clinical cases (N = 34). The diode response exhibited +/- 5% variation within +/- 20 degrees of the detector's marked "preferred" direction for the 6 MeV beam. Higher energy electron beams exhibited much less directional dependence. Dose rate response was found constant from 178-326 cGy/min (or 96-130 cm SSD). Energy dependence of response was constant within +/- 5.5% from 6-21 MeV. Dose response was linear (r2 = 0.999). Radiation field perturbation was significant at the depth of dose maximum (dmax). The maximum perturbation measured was -12.5% at dmax using the 6 MeV beam. Clinical trials of the system demonstrated that the diodes could be utilized for initial treatment quality assurance. The system proved effective for routine initial treatment electron beam in vivo dosimetry when the directional and energy dependent limitations of the system were respected.

Dose-Response Relationship, Radiation↗

PubMed1996

Age and sex differences in body size and composition during rhesus monkey adulthood.

Body size and composition were measured in forty-one adult Rhesus monkeys (Macaca mulatta) in order to characterize changes that occur during later life for both genders. Data were obtained by traditional somatometric techniques and by dual-energy X-ray absorptiometry. Representative monkeys were chosen within six categories defined by age (Young Adult, 6-9 year-old; Middle Aged, 15-19 year-old; Older Adult, 26-30 year-old), and sex. Body weight and most external measures of body size were greater during middle age and later life than in young adulthood, as were body fat content and lean body mass. Females tended to have a higher percentage body fat than males in all age categories. Lean tissue mass was markedly greater in the two younger groups for both sexes, compared to older adults. Bone mineral content and density were higher in the males than the females, but differences in bone mineralization among age groups did not achieve statistical significance. Such data derived from adult nonhuman primates are useful for defining fundamental biological changes with age in these species, and have value as a comparative model for studies of human aging and age-related morbidity.

Adipose Tissue↗

PubMed1995

Intercomparison of normalized head-scatter factor measurement techniques.

Normalized head-scatter factors were measured with cylindrical beam coaxial miniphantoms and high purity graphite buildup caps for 4-, 6-, 10-, and 24-MV photon beams at field sizes from 4 x 4 to 40 x 40 cm2. The normalized head-scatter factors determined by the two methods matched well for 4- and 6-MV photon beams. The miniphantom technique produced normalized head-scatter factors 1.5% and 4.8% lower than the buildup caps for the 10- and 24-MV beams for large field sizes, respectively. At small field sizes, the miniphantom technique produced larger normalized head-scatter factors than the buildup caps. Measurements made with an electromagnet indicate that a significant portion of the ionization measured in the buildup cap at 24 MV arises from contamination electrons. Measurements made with the miniphantom and magnet found no contamination electron contribution. The miniphantom technique may exclude such contamination electrons, potentially leading to inaccuracies in tissue-maximum ratios and phantom scatter factors, as well as inaccuracies in monitor unit calculations.

Humans↗

PubMed1995

Dosimetric characterization of radiosurgical beams with a diamond detector.

Dosimetric characteristics of small diameter 6 MV photon beams for a commercial radiosurgery system have been measured in a solid water phantom with a new diamond detector and compared with measurements using a p-type Si photon diode, small volume cylindrical and parallel plate ionization chambers, and radiographic films. Tissue maximum ratios (TMR) and total scatter factors (S c.p) were measured with the three ionometric (diamond, diode, ion chamber) detectors for 12 circular beams ranging in diameter from 12.5 to 40 mm. The TMR values obtained with the three ionometric detectors agreed well (+/- 1%) for all cone sizes and depths investigated when the displacement of the sensitive volume of the detector from its front surface is taken into account. The S c.p factors obtained with the ionometric detectors also agreed well (+/- 1.2%) for field sizes greater than 20 mm in diameter. For smaller field sizes, the cylindrical and parallel plate chambers measure a smaller S c.p factor, as a result of the steep dose gradients across their sensitive volumes. Cross-beam profiles acquired with the diamond detector agree well with the measurements with the diode detector and radiographic film. A distortion in the measured profiles in terms of broadened penumbra is observed with a small volume cylindrical ionization chamber.

Biophysical Phenomena↗

PubMedDate not supplied

Temperature-dependent versus constant-rate blood perfusion modelling in ferromagnetic thermoseed hyperthermia: results with a model of the human prostate.

Finite-element solutions to the Pennes bioheat equation are obtained with a model of a tumour-containing, human prostate and surrounding normal tissues. Simulations of ferromagnetic hyperthermia treatments are conducted on the tissue model in which the prostate is implanted with an irregularly spaced array of thermoseeds. Several combinations of thermoseed temperatures with different Curie points are investigated. Non-uniform, constant-rate blood perfusion models are studied and compared with temperature-dependent descriptions of blood perfusion. Blood perfusions in the temperature-dependent models initially increase with tissue temperature and then decrease at higher temperatures. Simulations with temperature-dependent versus constant-rate blood perfusion models reveal significant differences in temperature distributions in and surrounding the tumour-containing prostate. Results from the simulations include differences (between temperature-dependent and constant-rate models) in (1) the percentage of normal tissue volume and tumour volume at temperatures > 42 degrees C, and (2) temperature descriptors in the tumour (subscript t) and normal (subscript n) tissues including Tmax.t, Tmin.t and Tmax.n. Isotherms and grey-scale contours in the tumour and surrounding normal tissues are presented for four simulations that model a combination of high-temperature thermoseeds. Several simulations show that Tmin.t is between 1.7 and 2.6 degrees C higher and Tmax.n is between 2.1 and 3.3 degrees C higher with a temperature-dependent versus a comparable constant-rate blood perfusion model. The same simulations reveal that the percentages of tumour volume at temperatures > 42 degrees C are between 0 and 68% higher with the temperature-dependent versus the constant-rate perfusion model over all seed combinations studied. In summary, a numerical method is presented which makes it possible to investigate temperature-dependent, continuous functions of blood perfusion in simulations of hyperthermia treatments. Simulations with this numerical method reveal that the use of constant-rate instead of temperature-dependent blood perfusion models can be a conservative approach in treatment planning of ferromagnetic hyperthermia.

Body Temperature Regulation↗