SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
The technique of boron neutron capture therapy in the treatment of cerebral gliomas depends upon the selective loading of the tumor with a 10B-enriched compound and subsequent irradiation of the brain with low-energy neutrons. The charged particles produced in the 10B (n,alpha) 7Li reaction have ranges in tissue of less than 10 mum so that the dose distribution closely follows the 10B distribution even to the cellular level. The effectiveness of this therapy procedure is dependent not only on the 10B compound but on the spectral characteristics of the neutron source as well. Hence, an optimization of these characteristics will increase the chances of therapeutic success. Transport calculations using a neutral particle transport code have been made to determine the dose-depth distributions within a simple head phantom for five different incident neutron beams. Comparison of these beams to determine their relative therapeutic efficacy was made by the use of a maximum useable depth criterion. In particular, with presently available compounds, the MIT reactor (MITR) therapy beam (a) is not inferior to a pure thermal neutron beam, (b) would be marginally improved if its gamma-ray contamination were eliminated, (c) is superior to a partially 10B-filtered MITR beam, and (d) produces a maximum useable depth which is strongly dependent upon the tumor-to-blood ratio of 10B concentrations and weakly dependent upon the absolute 10B concentration in tumor. A pure epithermal neutron beam with a mean energy of 37 eV is shown to have close to the optimal characteristics for boron neutron capture therapy. Futhermore, these optimal characteristics can be approximated by a judiciously D2O moderated and 10B-filtered 252Cf neutron source. This tailored 252Cf source would have at least a 1.5 cm greater maximum useable depth than the MITR therapy beam for realistic 10B concentrations. However, at least one gram of 252Cf would be needed to make this a practical therapy source. If the moderated 252Cf source is not 10B filtered, the resultant neutron beam has characteristics similar to those of the MITR beam with no gamma-ray contamination. For usch a beam, 100 mg of 252Cf would produce a flux of 2.4 X 10(8) neutrons/(cm2 sec), which is an intensity suitable for therapy applications.
Human lymphocytes were irradiated in vitro during G0 stage by graded doses of thermal neutrons and of neutrons with mean energy of 0.04; 0.09; 0.35; 0.85 and 14.7 MeV as well as by 60Co gamma-rays. The data were fitted to the linear and linear-quadratic relations. The neutrons of low and intermediate energies showed the linear dependence on the dose, 14.7 MeV neutrons and gamma-rays--a linear-quadratic one, whereas the data obtained with 0.85 MeV neutrons fitted well the both models. Terminal and interstitial deletions produced by both gamma-rays and neutrons showed different dependencies upon the dose. Some qualitative pecularities of aberration spectra were found in the experiments with neutrons as compared with the data on gamma-irradiation: the ratio of exchanges to fragments was greater, and aberrations of chromatid type were produced. The specially designed experiments and calculations showed that the last effect was not connected with induced radioactivity.
Neutron energy spectra and yields produced by the bombardment of thick lithium targets by deuterons and protons have been measured using the time-of-flight method. Measurements were made at angles up to 45 degrees for deuteron energies of 8, 12 and 15 MeV and a proton energy of 15 MeV. The average neutron energy of the (d, n) reactions is shown to vary approximately as 0.44Ed. The (p, n) reaction has En = 4.7 MeV. The tissue penetration of neutron therapy beams is dependent on their average neutron energy and thus the low average neutron energy for these reactions appears to preclude their use for practical neutron therapy at these incident particle energies.
In this report is specified which accuracies must now be achieved in the determination of dose components for neutron therapy of tumors and for evaluation of RBE's after neutron irradiations of various organs from mammals or men. After these introductory remarks the reasons are summarized why the errors in ionimetric measurements of neutron doses are considerably higher than those of gamma-doses. In detail the concept and the errors of the Rossendorf neutron dosimeter system are represented. The latter consists of two spherical homogeneous ionization chambers, each of which is connected to a commercial dosimeter. The results of an intercomparison between our neutron dosimeter and that of DR. Bewley (MRC Cyclotron Unit, Hammersmith Hospital London) carried out at the Rossendorf neutron therapy facility are reported.
Methods of assessing the uniformity of thermal and fast neutron fluence in relation to total body in vivo neutron activation analysis are described. Results are presented for 14 MeV neutrons emitted by sealed tube generators housed in a massive concrete shield, representing a substantial source of neutrons degraded in energy. Optimisation of conditions for patient irradiations is discussed and it is shown that acceptable uniformity of fluence can be achieved with little or no premoderation of the incident neutrons.
A novel method is proposed of accurately measuring fast neutron doses of interest in radiotherapy. The technique, which utilizes calculated neutron fluence-to-kerma conversion factors, is based upon the combination of measurements with calibrated neptunium-237 and uranium-238 pulse fission chambers to obtain a response which matches the variation of kerma with neutron energy. The theoretical performance of a practical instrument has been assessed for a variety of neutron spectra to evaluate the spectrum dependence of the dosemeter. The overall systematic uncertainty using this absolute method of determining the neutron dose under charged particle equilibrium conditions is comparable to that encountered with ionization chamber techniques.
Human lymphocytes were irradiated in vitro during Go stage by graded doses of thermal neutrons and neutrons having an average energy of 0.04; 0.09; 0.35; 0.85 and 14,7 MeV as well as by 60Co gamma rays, and RBE of neutrons relative to gamma-rays was calculated for the frequency of total and different types of aberrations. It was found that the RBE has the most value at the low doses and decreases when the exposition dose increases. 0.35 MeV neutrons have the maximum RBE in comparison with neutrons having other energies. When comparing the RBE values calculated for different types of chromosome aberrations, it was found out that dicentrics and dicentrics plus centric rings had more RBE than acentric aberrations (pair fragments and minutes).
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.
Mice were whole-body-irradiated with 5 fractions of roentgen rays in 5 days, 5 fractions of cyclotron neutrons in 5 days, or with mixed neutron-photon fractionated radiation, in the sequence n-n-x-x-x or n-x-x-x-n. The LD50/4 day values were determined. Roentgen rays and neutrons interact in the additive manner in the mixed fractionation schemes: effective dose per fraction is as predicted from the roentgen ray-only and neutron-only experiments. This essentially agrees with HENDRY et coll. (1976). However, no trend was found towards a less-than -additive effect which was observed by those authors and has also been suggested in skin response to mixed schemes (NELSON et coll. 1975).
Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques and the dose distribution was measured using a 1/2 in. spherical "tissue-equivalent" proportional counter filled with "tissue-equivalent" gas.
Zero-degree neutron energy spectra for the p(41)-Be and d(49)-Be reactions were measured by time-of-flight for neutrons with energies above 1.9 and 1.4 MeV, respectively. Spectral changes resulting from the addition of copper, aluminum, and polyethylene filters to unfiltered beams were determined. Integral yields, average energies, filter material attenuation coefficients, and kerma fractions were computed for these spectra. Calculated spectra for neutron beams filtered by various thicknesses of polyethylene compared favorably with experimental results
In this report the physical and technical bases for the realization of neutron therapy in the GDR are summarized. As neutron source a thick beryllium target which is bombarded by 13.5 MeV deuterons from the Rossendorf cyclotron is used. Dose components are measured by paired homogeneous spherical ionization chambers of polythene and graphite. The arrangement of the whole irradiation plant is resumed.
The threshold foil technique has been used to investigate the behaviour in tissue of the spectra of neutron beams produced by the bombardment of thick Be targets with 13-0 and 20-5 MeV deuterons. The results indicate a gradual "softening" with depth in tissue of the spectrum generated by 20-5 MeV deutrons which contrasts with a gradual hardening as reported by other authors. This is discussed in terms of the significance of field size and the methods used for data collection and analysis.
Barley seeds were irradiated in the active zone of the reactor at 500 watt, at favourable flux of fast neutrons in the dose interval of 823--2144 rad. Seeds after irradiation were "cooled" for 48 hours, then germinated, and the length of shoots of the seven days old seedings was measured. The value of the half lethal dose is 1130 rad, estimated from the growth curve. There is a well-defined relation of chlorophyll content (calculated for fresh weight unit) to the dose used. It was concluded from the phenotype of the leaves that the decrease of chlorophyll content was due first of all to the presence of chlorophyll-less cells and cell lines and not to the decrease of chlorophyll content of the individual cells. Irradiation yielded genetically defected cells.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.