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At least 163 records · Page 9Linked to original sources
PubMed1989

Biological effectiveness of neutrons and pi-mesons in gut, bone, and transplantable tumours.

At the Munich RENT-facility a screening project was performed to define the biological characteristics of a fission neutron beam envisaged for radiotherapy. The quantitative endpoints used were jejunal crypt survival, late rectal stenosis in rats, osseous healing in traumatized rat femur and regrowth delay of murine transplantable tumours. The results obtained in normal tissues (with the possible exception of bone) demonstrate a high RBE, in accordance with the well documented dependence of RBE on neutron energy. The RBE-values measured in tumours after single dose treatment endorsed the high effectiveness, although--as has been the case with other beams--they gave no conclusive evidence of a therapeutic advantage. Nevertheless, the specific beam characteristics, i.e. a high RBE at the surface and a fast decline of the biologically effective depth dose suggest possible advantages of the RENT beam when applied in the treatment of selected superficial tumours.

Animals↗
PubMed1994

The response of Chinese hamster V79-379A cells exposed to negative pi-mesons: evidence that increased radioresistance is dependent on linear energy transfer.

Chinese hamster V79-379A cells exhibit low-dose hypersensitivity to 250 kVp X rays followed by an increased radioresistant response over the dose range 0.5-1 Gy. This phenomenon is not seen with neutrons (Marples and Joiner, Radiat. Res. 133, 41-51, 1993). It was therefore postulated the induction of radioresistance might develop as a response to a cellular event(s) which predominates after low- and not high-LET radiation. To test this hypothesis, we measured the survival response of V79-379A cells exposed to pions. Clonogenic survival was assessed for cells irradiated in the Bragg peak (35 keV/microns) and plateau region (10-20 keV/microns) of the beam, using an automated microscope (DMIPS cell analyzer). As expected, peak pions were found to be more effective per unit of dose at killing cells than plateau pions. The survival curve for cells irradiated in the plateau of the pion beam was found to incorporate a region of low-dose hypersensitivity and increased radioresistance, the effective D0 was dose-dependent, ranging from 3.5-5. This was not seen with peak pions, where the effective D0 was, on average, constant reflecting a single-exponential survival curve. Fitting the data with an induced repair model indicates that the phenomenon of increased radioresistance is almost certainly dependent on LET.

Animals↗
PubMed1979

Pre-clinical studies of the negative pi-meson beam at TRIUMF.

The pi- flux from the biomedical channel at TRIUMF increases with increasing channel momentum, while the contaminating electron flux decreases. Since the electrons appear to result from conversion of the high energy gamma-rays produced by pi0 decay in the production target, the electron contamination can be reduced further by target configurations which minimize gamma conversion. The attenuation of pi- beams by in-flight interactions was found to decrease from an initial value of 1.67 +/- 0.02% per g/cm2 at zero depth to 1.48 +/- 0.02% per g/cm2 near the stopping peak. The inactivation of cultured CHO cells by an extended-peak pi- dose distribution has been measured using the gel technique. The survival data have been fitted by a model which characterizes the physical quality of the dose profile by means of measured star densities. This model provides a convenient method of analysis for large sets of survival data and may be useful for prediction of the biological effect of new pi- dose distributions. The RBE value for 50% survival measured at the centre of a 7 cm extended peak was found to be approximately 1.4, in reasonable agreement with recent values obtained at LAMPF and SIN.

Animals↗
PubMed1979

Effect of negative pi mesons on vascular permeability of brain in neonatal rats.

Neonatal rats and their radiation-induced cerebral petechial hemorrhages were used as an experimental system for evaluating the effects of negative pions on healthy tissue and especially on the microvasculature. Dose response curves for peak and plateau pions (dose range 150--250 rad and 100--400 rad, respectively) were obtained and compared with those of 200 kV X-rays of corresponding dose rates. The RBE of the peak pions was 1.1, that of the plateau pions 0.6 resulting in a peak/plateau ratio of 1.8. Implications were made as to the importance of this favorable peak/plateau relationship since the response of the capillary endothelium to pion-irradiation might be one of the limiting factors in radiotherapy.

Animals↗
PubMed1980

The induction of chromosome aberrations in human lymphocytes by negative phi-mesons under conditions of anoxia and oxygenation.

After a dose of 3.0 Gy in the peak position of the pion depth-dose curve, the ratios between observed chromosome aberration yields under conditions of oxygenation and of anoxia were obtained for lymphocytes exposed at 3 depths in a plastic phantom. These ratios were 3.7, 1.9 and 1.3 in the plateau, peak and post-peak positions, respectively, suggesting a corresponding decrease in the oxygen enhancement ratio.

Aerobiosis↗
PubMedDate not supplied

Basic and applied research at the TRIUMF meson factory.

The TRIUMF 520 MeV H- cyclotron produces intense beams of protons, pions and muons supporting basic research in nuclear, particle and solid-state physics, nuclear chemistry and biomedicine, and applied research in electromagnetic breeding of nuclear fuel, proton radiography, radioisotope production and cancer treatment.

Animals↗