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PubMed1976

Some in vivo effects of pi mesons in mice.

The effect of 70 MeV pi mesons was studied to determine the effectivness of such beams aginst normal tissues in vivo. The end points included thymic weight loss, oocyte and bone marrow CFU-S survival and the induction of macroscopid lens opacities. The results indicate that pi mesons are not signifacantly more effective for these end-points than more conventional radiation sources such as 60Co gama rays, 220 kVp X rays, and 14 MeV X rays and electrons. Nor was there any detectable difference in RBE between the peak and plateau regions of the pi meson beam. The significance of these findings is discussed in relation of the the published pi meson RBE values of between 1 therefore 4 and 5 therefore 0.

Animals↗
PubMed1976

Response of HeLa cells to irradiation with pi- mesons.

HeLa cell suspensions were irradiated at various depths of Perspex in a beam of 70 MeV pi- mesons. The dose-rate in the Bragg peak varied between 40 rad hour-1 and 150 rad hour-1. The cells were assayed in vitro for loss of reproductive integrity. The results for irradiation in the peak indicated an RBE of about 2-1 when compared to the response obtained using 60Co gamma-rays at comparable dose-rates. At dose-rates of 100-150 rad hour-1, the RBE peak-to-plateau was about 1-4, while at lower dose-rates, the RBE peak-to-plateau was about 1.

Cell Survival↗
PubMed1976

Recovery in mammalian cells irradiated with a beam of pi--mesons.

HeLa cells have been irradiated in a beam of pi--mesons using fractionated exposures. The response-time curve for cells irradiated in the peak and in the plateau regions showed evidence of recovery. For cells irradiated in the post-peak position recovery was either absent or delayed.

Cell Survival↗
PubMed1977

Some long-term effects of negative pions in mice exposed to partial body irradiation.

The long-term effects of partial body exposure of one-day-old mice given either 60Co gamma rays or negative pions have been studied. Both radiations produced considerable life-shortening; for pions 6.8 +/- 1.5% of life is lost per 100 rad and for gamma rays the value is 5.7 +/- 0.5% per 100 rad. The RBE of pions for ten weeks of life-shortening is about 1.3 compared with 60Co gamma rays, although at lower doses the RBE may be higher reaching about two for six weeks of life shortening. The incidence rate of tumours at any particular age was greater in mice irradiated with pions at the peak and in those given higher doses of gamma rays than in the controls.

Age Factors↗
PubMed1978

Effects of negative pions and neutrons on the growth of Vicia faba bean roots.

Vicia faba bean roots have been irratiated with neutrons of various energies and with negative pi-mesons, and the effect on the ten-day growth of the roots has been determened. The neutron irratiations were made in beams of 400 and 600 MeV maximum energy, as well as with neutrons from a plutonium-beryllium source (mean energy 4.4 MeV) and from a 14 MeV neutron generator. The bean roots have also been irradiated at various points along the depth-dose curve of negative pi-mesons, including the gegion where the pions annihilate on coming to rest. The results show a maximum relative biological effectiveness (RBE) of 3.7 for 50% reduction in ten days growth for stopped negative pions and values up to 3.3 for high-energy neutrons, compared to 5.5 for 14 MeV neutrons. The biological effectiveness of high-energy neutrons and stopped pions shows a more pronounced dependence on dose than does the effect with lower-energy neutrons.

Dose-Response Relationship, Radiation↗
PubMed1979

OER and RBE for negative pion beams of different peak widths.

Experimental data on survival curves for pion because of different peak widths under aerobic and hypoxic conditions are reported. Metabolic depletion of oxygen by the Chinese hamster cells (line V79) was used to obtain hypoxia. The results indicate that the RBE at the beam entrance (plateau) is approximately 1.0. When the Bragg peaks were broadened to widths of 1.3, 7.8, and 10.5 cm (at the 80% dose level), the RBE (50% cell survival) at the peak centres was 1.7, 1.6, and 1.2, respectively. The OER at the entrance was 2.4 compared with about 2.9 for X rays. The OER was independent of the survival level at which it was measured. The OER at the peak centres at widths of 1.3, 7.8, and 10.5 cm was 2.1, 2.4, and 2.2, respectively. These results indicate that, although the RBE at the centre of the 10.5 cm wide peak was significantly lower than at the centres of the 1.3 and 7.8 cm peaks, the OER values are similar for all peak widths used in this study.

Animals↗
PubMed1980

The measurement of effective photon energy and "linearity" in computerized tomography.

Two liquid systems have been developed for the measurement of effective photon energy (Eeff) and "linearity" in computerized tomography (CT). A group of sixteen "keV liquids" enables an Eeff to be rapidly determined, by comparing the CT numbers of the specially formulated organic liquid mixtures with similar data for water. The "linearity" of the CT scanner, relating CT nubers to linear attenuation coefficients, may be investigated using 14 selected organic "linearity liquids". Details of these systems, together with some typical results, are presented.

Elementary Particles↗
PubMed1980

Effective measuring point of ion chambers for photon dosimetry in phantoms.

The effective point of measurement for spherical ionization chambers has been determined for 60Co and 137Cs gamma rays and for 300 kV X rays inside a water phantom. For reasons of comparison, measurements were also performed with a thimble-type Baldwin-Farmer ion chamber. For spherical ion chambers the displacement correction factors were 1-(0.37 +/- 0.04) r. 10(-2) for 60Co gamma rays and 1-(0.22 +/- 0.05) r. 10(-2) for 137 Cs gamma rays, where r is expressed in mm, whereas no displacement was observed for X rays. The differences in displacement obtained for the various types of radiation can be attributed to differences in attenuation and scatter characteristics of the various radiation qualities.

Elementary Particles↗
PubMed1981

Induction of spinal cord paralysis by negative pi-mesons.

As part of our investigations on late non-neoplastic injury induced by negative pi-mesons (pions), a series of studies have been performed using pion beams for the induction of spinal cord paralysis in the Fisher 344 rat. Groups of rats were exposed to 1, 5 or 15 daily doses of peak pions or X rays. Paralysis appeared earlier after treatment with pions than after X rays even in a comparison of groups with similar final incidences. A single dose RBE for spinal cord paralysis of 1.3 was found. The RBE rises to a value of 3.2 if the total dose is given as a series of 15 daily exposures. These RBEs are far larger than we have observed using other late injury end-points, such as tubular degeneration in the kidney or fibrosis and sclerosis in the support structures of the colon for which the single dose RBE is less than 1.2. The biological and/or physical basis for the high sensitivity of the spinal cord to peak pions has not yet been resolved, but these data have suggested caution in exposing the spinal cord to peak pions in our clinical trials.

Animals↗
PubMed1981

Negative pion depth-dose profile examined by means of HeLa cell-survival curves.

HeLa cells were irradiated at liquid nitrogen temperature with negative pions from Nimrod at the Rutherford Laboratory and then assayed for survival of colony-forming ability. Complete dose-response curves were obtained from repeated determinations at 14 different positions along the depth-dose profile and survival curves were fitted to the data by computer programme. A depth-damage profile was thus established in terms of the final slopes of these survival curves. This confirmed the expected RBE value of 1.84 at the ionization peak. Although a value of unity was found in the main plateau region, the "entrance" positions showed significantly higher values.

Cell Survival↗
PubMed1981

Tolerance of the mature human central nervous system to photon irradiation.

Tolerance of mature human brain to photon irradiation is described. Isoeffect curves have been derived for tolerance of large and small volumes of brain, by examination of doses determined empirically and in clinical use. These have been compared with isoeffect curves of thoracic myelitis, optic nerve and chiasm damage, and brain necrosis. The results show that the best-fitting Ellis-type equations, when five fractions per week are used, have low exponents for overall treatment time and high exponents for the number of increments (N), and are similar to published data on rat myelitis. Of the equations used to test the relationship between total dose and number of increments, the power curve was the best fit. Mean values of exponents for N derived for brain and spinal cord tolerance were 0.4 or more. These were similar to values obtained for optic nerve and chiasm damage, though the data are more limited for this complication. Brain necrosis is observed at slightly higher doses probably because of a difference in the end-point observed rather than because of any fundamental difference in tissue response. Evidence is presented to suggest that some repopulation may occur in widely spaced schedules. The use of the Ellis equation derived from connective-tissue data is inappropriate for central nervous system tissue, and its use may lead to a substantial risk of overdosage. A plea is made for adequate documentation of treatment details when human data are reported. The importance of dose per fraction is emphasized.

Adult↗
PubMed1982

The effects of negative pions on spermatogonial survival in the mouse.

A study of the radiation effects of pi-mesons on the testes of the mouse has been carried out using the pion beam at the SRC Rutherford Laboratory. The cell killing effects on type B and intermediate spermatogonia have been assessed and compared with the effects of 20-0 kVp X rays, delivered at the same dose rate. It was found that not only did irradiation of the testes not disturb the kinetics of spermatogenesis, but also the RBE for pions measured in the Bragg peak and on the plateau was not significantly different from unity. The comparison of this result with those of others using other pion beams is discussed.

Animals↗