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Biomedical subjects

J N Bradbury

Publications and source records attributed to J N Bradbury.

8 recordsLinked to original sources
PubMed1985

Dosimetry comparison and characterisation of an Al K ultrasoft x-ray beam from an MRC cold-cathode source.

Ultrasoft x-rays of 0.3-5 keV have provided a unique tool for the investigation of intracellular mechanisms of radiation action in biological organisms, including mammalian cells. However, their use presents unique practical problems in dosimetry and experimental design. Detailed interpretation of the biological results requires reliable dosimetry and well characterised monoenergetic beams. This paper presents a comparison between two fundamentally different dosimetric techniques, namely the ionisation current in an extrapolation chamber and photon counts in a proportional counter. Agreement within 7% was obtained when these two methods were applied to an Al K x-ray beam (1.5 keV) from an MRC cold-cathode transmission target discharge tube as previously used in many biological experiments. Photographic film was calibrated as a relative dosimetric technique and used for investigation of the intensity uniformity of the radiation field. These techniques provide a comprehensive characterisation of the beam in the position of the biological cells, including photon flux (or absorbed dose rate), spectral purity (showing much less than 1% bremsstrahlung relative to characteristic Al x-rays) and uniformity over the irradiation area (within about 5% for mammalian cell irradiations).

Cell Survival↗
PubMed1983

A lyoluminescent tissue-equivalent dosemeter for pion therapy beams.

The light emitted when pion irradiated glucose is dissolved in luminol solution has been found to be proportional to the pion beam depth dose distribution in water as determined by a TE ionisation chamber. The lyoluminescence of glucose overlaps very closely with the response profile of the ionisation chamber to the 170 MeV/c pi--mesons giving a Bragg peak to plateau ratio of 3:1. In comparison, the thermoluminescence response of LiF (TLD-700) to pions has been found to deviate significantly from this ratio. The close tissue equivalence of glucose, non-toxicity and its excellent lyoluminescent retention properties are important advantages over currently used dosemeters in clinical pion therapy, especially when direct in vivo measurements are considered. Pion doses ranging between 0.5 Gy (50 rad) and 30 Gy (3000 rad) were measured with an accuracy +/- 5% and reproducibility 3-5%.

Elementary Particles↗
PubMed1978

Dose outside the treatment volume for irradiation with negative pions.

Irradiation of humans with negative pions requires a knowledge of the absorbed dose and radiation quality outside the primary pion beam. In conjunction with early clinical trials at LAMPF, experimental data have been obtained with microdosimetric techniques and multiwire proportional counters. Theoretical calculations have been made for the neutron contribution to the dose and are consistent with these data. Measurements were made with in 40 cm x 51 cm x 76 cm water phantom for a negative pion beam of initial momentum of 170 MeV/c, deltap = +/- 3MeV/c. The absorbed dose outside the treatment volume is the result of: (1) neutrons and photons from the pion interactions,(2) treatment room background and (3) peripheral muons, electrons and pions in the primary beam. The first two components are nearly isotropic and are congruent to 0.02% of the peak dose at a distance of 24 cm from the treatment volume; the third component is anisotropic and varies from 0.01 to 0.1% of the peak dose. Collimation of the bean increases the dose outside the treatment volume typically by 50%.

Elementary Particles↗
PubMed1978

Pion radiotherapy: studies with nuclear emulsions.

Nuclear emulsions were used to provide information on (1) the pion star distribution for a therapy beam; (2) star production as a function of pion energy and residual range in nuclear emulsion; (3) the distribution of nuclear framgent ranges in emulsion; and (4) the neutron energy spectrum and fluence produced by negative pion capture in tissue, during treatment of a patient. This last item is important for determining the whole-body dose delivered to a patient undergoing pion radiotherapy.

Elementary Particles↗
PubMed1977

Current status of clinical pion radiotherapy.

An RBE for acute skin reaction to peak pions, for a specific fractionation scheme, has been established at 1.40-1.44. The time of development of acute skin reactions varied in 2 patients with 30 metastatic skin nodules treated with doses varying from 1,175 to 1,951 peak pions and 2,350 to 3,901 rads of 100 kVp x rays. The reactions reached their peak approximately one week apart at all dose levels with both forms of radiation. No untoward effects have been seen in epidermis or subcutaneous tissues as late as 169 days after the start of treatment. All nodules disappeared and have not returned 169 days after treatment. There is a strong suggestion that the response of thick tumors is sensitive to the proportion of high LET radiation deposited at various levels in the tumor.

Dose-Response Relationship, Radiation↗
PubMed1976

Initial comparative response to peak pions and x-rays of normal skin and underlying tissue surrounding superficial metastatic nodules.

Given the limitations of available material and methods for measuring skin response, the relative biological effectivenss (RBE) for the development and healing of skin reaction to pions in this experiment is 1.43. This is based on data obtained from a patient with malignant melanoma, in whom multiple skin nodules and the surrounding normal skin were randomized into three dose levels for pions and x-rays. The RBE for skin reaction was obtained while the skin tumor nodules appeared to regress at least as rapidly with pion therapy as with x-rays. Without benefit of adequate observation of time required for nodule regrowth, any estimate of tumor RBE is speculative.

Dose-Response Relationship, Radiation↗