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Biomedical subjects

P M DeLuca

Publications and source records attributed to P M DeLuca.

32 records · Page 2Linked to original sources
PubMed1984

The survival of parenchymal hepatocytes irradiated with low and high LET radiation.

We have developed an in vivo clonogenic assay system for parenchymal hepatocytes which has enabled us to investigate the reproductive survival and repair capacity of liver cells exposed to genotoxic agents. In this report we present our results with hepatocytes irradiated 60Co and neutrons. The survival curve for parenchymal hepatocytes enzymatically dispersed 30 min after exposure to 60Co has a D0 value of 2.7 Gy and an extrapolation number insignificantly different from unity. However, when the hepatocytes were allowed to remain in situ for 24 h before being assayed for survival, the extrapolation number significantly increased to 2.3, whereas the D0 value remained unchanged. Therefore, normal parenchymal hepatocytes in G0 are able to repair potentially lethal damage (PLD) after exposure to 60Co and this repair phenomenon is expressed solely as an increase in the n value. In contrast, with hepatocytes exposed to 14.3 MeV neutrons, the survival curve is exponential with a D0 value of 1.7 Gy regardless of whether the cells remained in situ for 30 min or 24 h before the assessment of their reproductive survival. A comparison of the 60Co and neutron survival curves, where 24 h is allowed for PLD repair to occur, demonstrates that the RBE of neutrons for hepatocytes increases with decreasing dose and equals 4.2 at 50 cGy. The radioprotective agent WR-2721 was shown to act as a dose modifying agent with a DMF of 2.1, implying that it may be of potential clinical value as a radiation hepato-protective drug.

Amifostine↗
PubMed1984

Effect of pulsed dose in simultaneous and sequential irradiation of V-79 cells by 14.8-MeV neutrons and 60Co photons.

The effect of irradiating V-79 Chinese hamster cells with a mixture of 40% 14.8-MeV neutrons and 60% 60Co photons with simultaneous or sequential exposures is investigated. Sample doses are obtained by irradiating cells with alternating 3-min pulses of neutrons and photons (in the sequential case) or with mixed neutrons and photons followed by equal beam-off periods to ensure equal total exposure times for sequential and simultaneous irradiations. Differences between the survival results under each beam configuration that are consistent with previous observations with nonpulsed irradiations are observed.

Animals↗
PubMed1984

Kerma factor of carbon for 14.1-MeV neutrons.

Using microdosimetric techniques, a direct measurement was made of the kerma factor of carbon for 14.1-MeV neutrons. Kerma was inferred from charged particle energy depositions measured with a small graphite-walled proportional counter. Measurements with an ionization chamber and a proportional counter, both constructed with A150 plastic walls, as well as induced 24Na activity from the 27Al(n, alpha) reaction, determined the neutron fluence. The resulting carbon kerma factor was 0.178 +/- 0.11 X 10(-8) cGy X cm2 which is lower than published tabulations but in agreement with recent microscopic cross-section measurements.

Carbon↗
PubMed1983

V79 survival following simultaneous or sequential irradiation by 15-MeV neutrons and 60Co photons.

A unique tandem source irradiation facility, composed of an intense d-T neutron source and a 60Co teletherapy unit, was used to investigate biological responses for different neutron/photon configurations. V79 Chinese hamster cells, attached as monolayers in log-phase growth, were irradiated at 37 degrees C by either 14.8-MeV neutrons, 60Co, or a mixture of 40% neutrons and 60% photons in simultaneous or sequential application. Measurements of cell survival indicate an increased effectiveness in cell killing for simultaneously administered neutrons and photons compared to that measured or predicted for sequentially applied beam modalities. An understanding of the magnitude of these interactive effects is important both for calculating accurate effective doses for neutron radiotherapy of deep-seated tumors, for which the photon component is appreciable, and for determination of environmental hazards to people occupationally exposed to mixtures of photons and neutrons.

Animals↗
PubMedDate not supplied

Characteristics of A-150 plastic-equivalent gas in A-150 plastic ionization chambers for p(66)Be(49) neutrons.

The evaluation of a gas mixture having an atomic composition similar to that of A-150 tissue-equivalent (TE) plastic has been extended to a high-energy neutron therapy beam. "A-150" gas, air, and methane-based TE gas were each flowed through A-150 plastic-walled ion chambers of different sizes and irradiated with p(66)Be(49) neutrons. A tentative value for W(A-150) of 27.3 +/- 0.5 JC-1 was derived for this beam. The W value of the A-150 gas mixture is compared to those of methane-based TE gas and of air for the p(66)Be(49) neutron beam as well as to corresponding values found in similar experiments using 14.8-MeV monoenergetic neutrons.

Beryllium↗
PubMedDate not supplied

Performance characteristics of A 150 plastic-equivalent gases in A 150 plastic proportional counters for 14.8-MeV neutrons.

Two recently developed A 150 plastic-equivalent gas mixtures have been tested for suitability in proportional counter applications. Methane- and propane-based "tissue-equivalent" gases were also included for comparison purposes. Event-size weighted dose distributions were measured in a 14.8-MeV neutron beam. Resolution was found to be independent of gas mixture. Moreover the gains of the two A 150 mixtures were the same, and comparable to that of the methane-based gas mixture. The ionization yield per event size was also independent of the hydrogenous gas mixture employed. Neutron doses determined with the proportional counter were in reasonable agreement with those obtained from an ionization chamber.

Fast Neutrons↗
PubMedDate not supplied

Measurement of dose distributions of linear energy transfer in matter irradiated by fast neutrons.

A detector has been developed and used to measure dose distributions versus linear energy transfer to thin gas targets in spherical geometry from fast neutron irradiation of tissue-equivalent plastic and carbon. The detector is a hemispherical proportional counter with a Cs(T1) scintillator at the center of the hemisphere. The coincidence of the proportional counter signals constrain the measurements to charged particles traversing the radius of the hemisphere. The charged particle energy deposition distributions are directly measured for a known pathlength. The A-150 kerma factor was measured at a neutron energy of 14.8 MeV and is in agreement with tabulated values. The carbon kerma factor measurements are less than the tabulated value at 14.8 MeV. The alpha-particle production in carbon was measured for neutron energies from 14.1 to 14.8 MeV and is compared with existing data.

Energy Transfer↗
PubMedDate not supplied

A prototype beam delivery system for the proton medical accelerator at Loma Linda.

A variable energy proton accelerator was commissioned at Fermi National Accelerator Laboratory for use in cancer treatment at the Loma Linda University Medical Center. The advantages of precise dose localization by proton therapy, while sparing nearby healthy tissue, are well documented [R. R. Wilson, Radiology 47, 487 (1946); M. Wagner, Med. Phys. 9, 749 (1982); M. Goitein and F. Chen, Med. Phys. 10, 831 (1983)]. One of the components of the proton therapy facility is a beam delivery system capable of delivering precise dose distributions to the target volume in the patient. To this end, a prototype beam delivery system was tested during the accelerator's commissioning period. The beam delivery system consisted of a beam spreading device to produce a large, uniform field, a range modulator to generate a spread out Bragg peak (SOBP), and various beam detectors to measure intensity, beam centering, and dose distributions. The beam delivery system provided a uniform proton dose distribution in a cylindrical volume of 20-cm-diam area and 9-cm depth. The dose variations throughout the target volume were found to be less than +/- 5%. Modifications in the range modulator should reduce this considerably. The central axis dose rate in the region of the SOBP was found to be 0.4 cGy/spill with an incident beam intensity of 6.7 x 10(9) protons/spill. With an accelerator repetition rate of 30 spills/min and expected intensity of 2.5 x 10(10) protons/spill for patient treatment, this system can provide 50 cGy/min for a 20-cm-diam field and 9-cm range modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗