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F T Kuchnir

Publications and source records attributed to F T Kuchnir.

At least 19 recordsLinked to original sources
PubMed1992

A dosimetric study comparing three-, four-, and six- field plans for treatment of carcinoma of the prostate.

We present a three-dimensional dosimetric analysis of 3-, 4-, and 6-field plans using 24 MV photon beams for treatment of carcinoma of the prostate. We compare isodose distributions on a transverse plane through the center of the target as well as differential and integral dose volume histograms for the target and critical structures, respectively. An extensive study on a representative case led to the development of a technique where two complementary 3-field daily plans deliver the same daily target dose as the standard 4-field box while affording sparing of the bladder and rectum similar to that achieved with a 6-field plan. This technique was shown to yield the same results on a sample of four additional patients representing a range of target and patient sizes. We conclude that the combined two-day, 3-field method for treatment of the prostate may be a better choice than the standard 4-field box or the 6-field daily plan for dose escalation studies.

Humans↗
PubMed1991

3-D treatment planning and dose delivery verification integrating a variety of state-of-the-art techniques: a case report.

A patient previously treated with radiation for base-of-tongue cancer presented with recurrent disease seven years later. The spinal cord had received tolerance dose. Using state-of-the-art treatment planning techniques, including beam's-eye-view and volumetrics, dose-volume histograms, split field technique, mixed energies, and beam intensity modulation (with a compensator), we achieved uniform dose coverage of the target in 3-D. This was verified in vivo with thermoluminescence dosimeters positioned in the esophagus by means of a nasogastric tube that ran centrally through the target volume. The various techniques applied will be presented with a discussion of the rationale used in each step of plan optimization and verification.

Image Processing, Computer-Assisted↗
PubMed1990

Computer-aided construction and quantitative evaluation of missing-tissue compensators.

We have implemented a system for the design and construction of missing-tissue compensators for Radiation Therapy. The patient topography is obtained by Moire' photography. The thickness of lead required to compensate for a given amount of missing tissue was determined experimentally for three photo-beam energies and a combination of field sizes and geometries. With the aid of a computer, tissue deficit information is converted to isolead-thickness lines. These are used as input to a computer-controlled milling machine to fabricate the compensator. The effectiveness of compensation was evaluated in phantom and in vivo. This work describes the initial effort required to implement a program for compensation of tissue deficit at the patient's surface. It also introduces tools for assessing quantitatively the degree of dose uniformity which can be achieved using compensators in clinical applications.

Humans↗
PubMed1989

Beam's-eye-view aided treatment planning for a nasopharyngeal lesion: a case report.

We report on the application of CT-based multilevel treatment planning to achieve complete and uniform dose distribution over the entire target while sparing critical structures. Treatment strategy and parameters are chosen on the slice containing the isocenter. Target coverage and organ sparing is achieved on all other slices by independently adjusting the asymmetric field width at each level, stimulating the effects of custom blocks. The optimized field borders are back projected using beam's eye views (BEV) from each treatment angle. The BEV printouts are used to assist the physician in the delineation of field blocking on the simulation films.

Humans↗
PubMed1989

Effect of lung-density correction in treatment planning for tangential-fields breast irradiation: a case report.

We report on the effect of lung-density correction on dose distribution in a transverse slice containing the isocenter for tangential-fields breast irradiation. In this case study we analyzed the target coverage as well as hot spots for four types of treatment plans: Plan 1 assumes uniform unit density throughout, Plan 2 utilizes all the treatment parameters of Plan 1, but takes into account the lower lung density. Plan 3 is generated by optimizing the dose distribution in the presence of the lower lung density, and Plan 4 is an improvement on Plan 3 by using custom instead of standard wedges. Our analysis shows that consideration of the lower lung density is important for optimal treatment planning for the breast and that specially designed wedges can improve the dose distribution.

Breast Neoplasms↗
PubMed1979

Energy dependence of the neutron sensitivity of C--CO2, Mg--Ar and TE--TE ionisation chambers.

The neutron sensitivity relative to 60Co of commercially available C--CO2, Mg--Ar and TE--TE ionisation chambers was measured as a function of energy from 1 to 44 MeV. The sensitivity function was obtained by the method of Kuchnir, Vyborny and Skaggs from differences in measurements made at two angles in mixed fields having an isotropic gamma-ray component. Such fields were produced by bombardment of a thick beryllium target with 16 and 28 MeV deuterons, 44 MeV 3He-ions and 35 and 46 MeV protons. The results show that the relative neutron sensitivity of the C--CO2 and Mg--Ar chambers increases continuously with energy, whereas that of the TE--TE chamber is relatively constant.

Argon↗
PubMed1978

Dosimetric properties of neutron beams from the D--D reaction in the energy range from 6.8 to 11.1 MeV.

The tissue kerma in air, the tissue dose at maximum build-up, the relative depth dose on the central axis and the dose build-up characteristics were measured for neutrons produced by 6.8, 8.9 and 11.1 MeV deuterons on deuterium. The neutron beams were produced by a variable-energy cyclotron with a fully stopping deuterium gas target 20 cm long. Measurements were made in a 11.1cm x 11.1 cm field 126 cm from the target entrance window. The dose rate was found to increase rapidly with energy from 0.07 rad min-1 microamperemeter-1 at 6.8MeV to 0.35 rad min-1 muA-1 at 11.1 MeV. The entrance dose is about 50% of the dose maximum for each bombarding energy. The depth of the 95% dose level in the build-up region increased from 50 mg cm-2 at 6.8 MeV to 90 mg cm-2 at 11.1 MeV. The penetration was independent of the bombarding energy in the region investigated. Attenuation of the total dose to 50% of the maximum occurred at 10.2 +/- 0.1 g cm-2 for all three bombarding energies. The dose at the maximum is typically 14% higher than the tissue kerma in air.

Atmosphere↗
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

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↗