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Biomedical subjects

F T Kuchnir

Publications and source records attributed to F T Kuchnir.

34 records · Page 2Linked to original sources
PubMed1978

The use of 10B to enhance the tumour dose in fast-neutron therapy.

Incorporation of 10B in tumours treated by fast-neutron therapy would increase the tumour dose via the reaction 10B(n, alpha)7Li which occurs with partially thermalised neutrons. The extent of the dose enhancement was measured for neutron beams with median energies of 2.4, 3.3, 7.0 and 9.0 MeV by two techniques: with a BF3 proportional counter in three beams and activation of 23Na in the fourth. The results obtained with the two techniques are in good agreement. The magnitude of the dose enhancement depends upon the depth, field size and neutron beam energy. The dose enhancement at a depth of 8 cm varied from 0.32% with the lowest-energy beam to 0.07% with the highest-energy beam for each microgram of 10B uptake per gram of tissue. The products of the reaction in 10B would, however, have an RBE about twice that of the fast-neutron dose in the absence of boron. The method may be useful if drugs providing adequate uptake of 10B can be synthesised.

Beryllium↗
PubMed1977

Comparison of two independent methods for determining the neutron/gamma sensitivity of a dosemeter.

Results obtained with two independent methods for measuring the n/gamma sensitivity of non-hydrogenous dosemeters are compared for the neutron beam produced by 8.3 MeV deuterons on beryllium. In one method, a pure neutron field is simulated by taking the difference between measurements made at diffrent angles in a mixed field with an isotropic gamma-ray component. In the second method, the mixed (n+gamma) beam is purified by lead filtration. An assumption in the lead filtration method is that the background radiation is invariant under three different beam conditions. This assumption was found not be be valid in our experimental arrangement; and caused the values obtained for the n/gamma sensitivity to be systematically high. A modification was made in the lead filtration method so that the dosemeter response to background could be determined for each beam condition. Good agreement was obtained between the results of the spectral difference and modified lead filtration methods.

Air↗
PubMed1975

A new method for determining the neutron response function of "neutron insensitive" dosimeters. Method and preliminary determinations.

Charged-particle bombardment of thick beryllium targets produces a neutron yield varying with angle, and an isotropic gamma component. Differences in detector response in such a field are due to neutrons alone. With accurate neutron spectral distributions and measurements of detector response, a computer code can be used to determine the neutron sensitivity of the detector as a function of energy.

Computers↗
PubMedDate not supplied

Neutron spectra.

Explore the source record for details and available documents.

Neutrons↗
PubMedDate not supplied

Neutron spectra from 35 and 46 MeV protons, 16 and 28 MeV deuterons, and 44 MeV 3He ions on thick beryllium.

The energy spectra of neutrons produced by 35 and 46 MeV protons, 16 and 28 MeV deuterons, and 44 MeV 3He ions on thick beryllium were measured at angles of 0 degrees, 15 degrees, and 45 degrees with respect to the incident beams. The spectra were measured by the time-of-flight method for neutrons from the maximum energy down to 1 MeV. Neutron dose rates obtained from the zero-degree spectra by use of available tissue kerma factors agree with TE-TE ionization chamber measurements.

Beryllium↗
PubMedDate not supplied

Neutron dose equivalent next to the target shield of a neutron therapy facility using an LET counter.

The use of a spherical tissue-equivalent proportional counter for measurements of the lineal energy (y) and derivations of the linear energy transfer (LET) for fast neutrons has the advantage of giving distributions of dose and dose equivalent as functions of either LET or y. A measurement next to the target shielding of the neutron therapy facility at the University of Chicago Hospitals and Clinics (UCHC) is described, and the data processing is outlined. The distributions are presented and compared to those from measurements in the neutron beam. The average quality factors are presented.

Energy Transfer↗
PubMedDate not supplied

Determination of the source position for the electron beams from a high-energy linear accelerator.

We have investigated the energy and field-size dependence of the source position of the electron beams from a Varian Clinac-2,500 accelerator. Three independent experimental methods were used: (1) multipinhole camera (MPC), (2) back projection of the full width at half maximum (FWHM), and (3) the inverse square law (ISL). The positions of the virtual and effective sources were calculated using the multiple Coulomb scattering (MCS) formalism. The results obtained from the MPC agree, within the experimental uncertainties, with the calculated values for the virtual source position. Similarly, the results from the FWHM method agree with the calculations with the exception of those for small field sizes at the lower energies. This is consistent with the fact that both kinds of measurements are not very sensitive to scattering in the photon and electron collimators. In contrast, the source position determined by the ISL method shows strong dependence on field size and energy, and does not agree with the values predicted by the MCS formalism. This is due to contamination from electrons scattered in the x ray and electron collimation system. The techniques and results reported here should be generally applicable to other scatter foil linear accelerators.

Electrons↗
PubMedDate not supplied

Correlation of microdosimetric measurements with relative biological effectiveness from clinical experience for two neutron therapy beams.

Microdosimetric measurements were made for the neutron therapy beams at the University of Chicago and at the Cleveland Clinic with the same geometry and phantom material using the same tissue-equivalent spherical proportional counter and standard techniques. The energy deposition spectra (dose distributions in lineal energy) are compared for these beams and for their scattered components (direct beam blocked). The model of dual radiation action (DRA) of Kellerer and Rossi is employed to interpret these data in terms of biological effectiveness over this limited range of radiation qualities. The site-diameter parameter of the DRA theory is determined for the Cleveland beam by setting the biological effectiveness (relative to 60Co gamma radiation) equal to the relative biological effectiveness value deduced from radiobiology experiments and clinical experience. The resulting value of this site-diameter parameter is then used to predict the biological effectiveness of the Chicago beam. The prediction agrees with the value deduced from radiobiology and clinical experience. The biological effectiveness of the scattered components of both beams is also estimated using the model.

Humans↗
PubMedDate not supplied

Characteristic parameters of 6-22 MeV electron beams from a 25-MeV linear accelerator.

Depth-ionization measurements were performed using a thin wall parallel plate chamber in water at nominal electron energies of 6, 9, 12, 15, 18, and 22 MeV for the standard available square field sizes. The characteristic parameters of the central axis depth-dose distributions were derived and compared to corresponding values for other accelerators. Vacuum packed therapy-verification films were used in water to obtain isodose distributions in a plane containing the central axis of the beam. The uniformity index and penumbra of the beams were measured from isodose distributions obtained in planes perpendicular to the beam central axis, at depths of 1/2R85 in water.

Electrons↗
PubMedDate not supplied

Dosimetry of Sr-90 ophthalmic applicators.

Sr-90 ophthalmic applicators are commonly used for the treatment of superficial eye disorders. Although a variety of dosimetric devices such as film, thermoluminescent dosimeters (TLD's), ion chambers, and radiochromic foils have been used to measure the peak dose at the applicator surface, there is no internationally agreed upon calibration procedure. Recently, large discrepancies among calibrations of the same applicator at three institutions have been reported. Here we describe a technique to obtain the peak dose rate at the applicator surface using LiF TLD's. The technique can be used for the calibration of flat as well as curved surface applicators. Results for two flat and three concave applicators are presented. Our measurement of the surface dose rate for one of the flat applicators is compared with those obtained by four other institutions, each using different dosimetric devices.

Calibration↗
PubMedDate not supplied

Measurement of the replacement correction factor for parallel-plate chambers in electron fields.

When parallel-plate chambers are used for dosimetry in electron fields, the AAPM dosimetry protocol recommends a value of 1.0 for the replacement correction factor, P(repl),pp,E, until further data become available. Here, P(repl),pp,E for five commercially available parallel-plate chambers was measured as a function of electron energy from a nominal value of 5.5 to 22 MeV by comparison with a cylindrical chamber whose P(repl),cyl,E was obtained from data in the protocol. Since this method is based on the concept of a constant value for Ngas,pp, the energy and modality dependence of Ngap,pp is also investigated for these chambers for Co-60, 4-, 6-, 24-MV photons and for 22-MeV electrons. It is found that for three of the chambers P(repl),pp,E is independent of energy, consistent with unity within one or two standard deviations (s.d.). For the fourth chamber P(repl),pp,E is similarly consistent with one above 10 MeV, but decreases at lower energies, while for the fifth one it shows a systematic drop with decreasing energy.

Calibration↗
PubMedDate not supplied

Experimental determination of fluence perturbation factors for five parallel-plate ionization chambers.

The calibration of parallel-plate chambers for absolute dosimetry is an unsettled matter. The medical physics community has not yet agreed on a practical method of obtaining Ngas, although several researchers are working on this problem. If the photon and electron fluence perturbation factors, KwallKcomp, were known for chambers of standard construction with full buildup provision, then an in-air Co-60 calibration could be applied to these, as is done with cylindrical chambers. We have obtained such correction factors for five commercially available chambers based on measurements in air and in homogeneous phantoms relative to matched cylindrical chambers of known dosimetric parameters. For three of the chambers (Markus, Holt and Exradin) we find that KwallKcomp = 1.000 +/- 0.008, in excellent agreement with available results from Monte Carlo calculations. The values for the other two chambers (NACP and Capintec) are different than 1. Our results are compared to recently published values, both calculated and measured.

Calibration↗