D. K. Bewley

The Effect of Oxygen on Impairment of the Proliferative Capacity of Human Cells in Culture by Ionizing Radiations of Different LET

SummaryOxygen-enhancement ratios (OER) have been determined for the inhibition of clone-formation by cultured cells of human origin irradiated with α-particles and deuterons of different energies, fast neutrons and 250 kvp x-rays. The results of experiments with mono-energetic charged particles, whereby narrow distributions of linear energy transfer (LET) are obtained, show that the OER decreases with increasing LET from about 2·6 at a LET∞ of 5·6 kev/μ of unit density tissue to a value of 2·05 at 61 kev/μ, followed by a more rapid decrease to 1·0 at 165 kev/μ. With fast neutrons, produced by bombarding Be with 16 mev deuterons, an OER of 1·6 was obtained and with 250 kvp x-rays the OER was 2·7.The relation between the relative biological effectiveness (RBE), the OER and the LET is discussed.

The response of pig skin to fractionated treatments with fast neutrons and X rays

Abstract The skin of pigs has been used to study the effect of fractionated irradiation with fast neutrons of mean energy 6 MeV. Six, nine and 15 fractions have been used over a period of three weeks, and two fractions divided by short intervals of time up to 24 hours. The effects of fractionated treatments with X rays are also summarised. The RBE of the neutron beam rises steadily from 2·3 for a single dose to 3·6 for 15 fractions. Observations up to five years after treatment have failed to show any sign of increased late reactions after neutrons. There is less recovery during a fractionated course of treatment with fast neutrons than with X rays, the relative amount of recovery being 0·6. Very little recovery was observed during the first seven hours after treatment with neutrons. Reactions occurring after fractionated treatments with X rays show that the number of fractions is more important than the time over which the treatment is extended, up to 28 days, but that prolongation is nevertheless a sign...

EXPERIMENTS WITH FRACTIONATED X-IRRADIATION OF THE SKIN OF PIGS. II. FRACTIONATION UP TO FIVE DAYS.

Fifteen fields on one pig were irradiated with 1, 2, 2, 3 and 5 fractions in 1, 5, 2, 3 and 5 days respectively. Skin reactions were recorded up to 80 or 100 days, so that the doses which produced equal reactions could be assessed. Three degrees of damage were analysed for early, medium and late reactions. As an example, the doses to produce one level of reaction over 30–85 days were respectively 2,050, 2,560–2,750, 2,750, 3,360 and 4,060 rads for the fractions listed above. The corresponding values of “DQ” = (Dn — D1)/(n —; 1) were high, 500–700 rads. The values of (Dn − D1)/(n − 1) became smaller with larger numbers of fractions. Two pigs were irradiated to investigate the “reciprocal vicinity” effect. It was found to be small for the field arrangements used, but the sensitivity of pig skin increased in the dorso-ventral direction and corrections were sometimes necessary. Two pigs were irradiated with pairs of equal doses separated by 0 to 24 hours. A recovery pattern was observed similar to that found ...

The Effect of Fractionation on Four Day Survival of Mice after Whole-body Neutron Irradiation

The proportion of animals surviving four days after whole body neutron irradiation is not altered by giving the radiation in two fractions separated by four to six hours. This result is compared with previously reported data after 250 kV X irradiation when it was found that a dose higher by 400–600 rads was necessary to produce the same killing effect if the radiation was given in two fractions rather than a single dose. This results in a larger RBE (250 kV/neutron) for the fractioned radiation than for single-dose irradiation and any increase in the number of fractions would increase the RBE further. These results may be relevant to the use of neutrons for therapy.

The Clatterbridge high-energy neutron therapy facility: specification and performance

A new high-energy neutron therapy facility has been installed at the Douglas Cyclotron Centre, Clatterbridge Hospital, Merseyside, in order to extend the clinical trials of fast neutrons initiated by the Medical Research Council. The neutron beam is produced by bombarding a beryllium target with 62 MeV protons. The target is isocentrically mounted with the potential for 360 degrees rotation and has a fully variable collimator. This gives a range of rectilinear field sizes from 5 cm x 5 cm to 30 cm x 30 cm. Basic neutron beam data including output, field flatness, penumbra and depth-dose data have been measured. For a 10 cm x 10 cm field, the 50% depth dose occurs at 16.2 cm in water and the output is 1.63 cGy microA-1 min-1 at the depth of dose maximum. The effectiveness of the target shielding and the neutron-induced radioactivity in the treatment head have also been measured. It is concluded that the equipment meets both the design specifications and also fully satisfies criticisms of earlier neutron therapy equipment. A full radiation survey of the centre was also carried out and it was found that radiation levels are low and present no significant hazard to staff.

LET as a Determinant of Bacterial Radiosensitivity, and Its Modification by Anoxia and Glycerol

Changes in radiosensitivity and in the radioprotection afforded by anoxia, glycerol, and other compounds have been studied as a function of LET in Shigella flexneri Y6R. The radiations used were 5-MeV electrons, 250-kVp X-rays, neutrons of mean energy 6 MeV, and beams of deuterons and helium nuclei in the range 60 to 800 MeV

Changes in relative biological effectiveness with depth of the Clatterbridge neutron therapy beam.

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PHYSICAL ASPECTS OF THE DEUTERON AND HELIUM NUCLEI BEAMS FROM THE M.R.C. CYCLOTRON.

. The bacteria were irradiated in suspension or on cellophane carriers. With the latter, an anomalously high value of oxygen enhancement ratio (o.e.r.) was observed for X-rays, this value being higher also than for bacteria irradiated in suspension. Except for this, o.e.r. decreased with increasing LET. Protection ratios were the same for neutrons and radiations of low LET on suspensions, and, with the latter, the ratios were lower than when cellophane carriers were used. While the aerobic protection ratio was lower for helium ions at 800 MeV

A comparison for use in radiotherapy of neutron beams generated with 16 and 42 MeV deuterons on beryllium

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Effects of Dose-rate on the Radiation Response of Rat Skin

than for other radiations, there was little change up to 500 meV