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Biomedical subjects

D K Bewley

Publications and source records attributed to D K Bewley.

At least 19 recordsLinked to original sources
PubMed1989

Changes in biological effectiveness of the neutron beam at Clatterbridge (62 MeV p on Be) measured with cells in vitro.

Chinese hamster V79 cells have been used to assess changes in RBE of the p(62)Be neutron beam at the Clatterbridge Hospital with depth in a phantom and with use of a hydrogenous filter. The cells were exposed at depths of 2 and 12 cm and at a depth of 2 cm with a hydrogenous filter. Two groups of experimenters each conducted two experiments. The ratios of relative biological effectiveness (RBE) at a depth of 12 cm to that at 2 cm were found by the two groups to be 0.99 +/- 0.04 and 0.96 +/- 0.02 (standard errors). The effect of a polythene filter 4.5 cm thick was measured at a depth of 2 cm and the ratio of RBE with and without the filter was found by both groups to be 0.99 +/- 0.02. All the experiments suggest that there may be small effects of beam hardening by depth and filtration but these results are in marked contrast with those obtained using an in vivo system.

Animals↗
PubMed1988

Anthropomorphic models for checking the calibration of whole-body counters and activation analysis systems.

Three models of the human body have been made for checking the calibration of whole-body counters and activation analysis systems. Their weights are 41, 67 and 110 kg. Each contains simplified forms of lungs, bones, thyroid, kidneys and liver and has a chemical composition similar to that of the ICRP standard man. In addition traces of toxic elements such as Cd and Hg have been included in various organs. The composition of the manikins has been measured at four centres where activation analysis in vivo has been carried out. The potassium contents have been measured at three other centres. Differences between measured and actual contents have often been much larger than quoted uncertainties of the measurements, 20-50% for Na, Cl and P. For K, differences did not exceed 17% but are still often greater than the expected uncertainty. The greatest errors usually occurred with the smallest manikin.

Activation Analysis↗
PubMed1988

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.

Calibration↗
PubMed1988

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

We have measured the biological equivalence of the Clatterbridge neutron therapy beam [p(62)-Be] and the Hammersmith neutron therapy beam [d(16)-Be] using the mouse intestinal crypt assay. The ratio (NDR) of Clatterbridge neutron (n + gamma) dose relative to Hammersmith neutron dose (n + gamma) was found to be 1.2-1.13 over a dose/fraction range of 1.8-9 Gy at 2 cm deep in a Perspex phantom. It is shown that the effectiveness of the Clatterbridge beam was reduced with penetration into the phantom because of hardening of the beam to a maximum reduction of 11% at 12 cm deep in the phantom. The hardening of the beam with depth of penetration will need to be taken into account by clinicians in assessing the tumour dose and tissue tolerance. Relative biological effectiveness values for the Clatterbridge and Hammersmith neutron beams were also measured. All neutron doses for both Hammersmith and Clatterbridge beams are total doses (n + gamma) which comply with the European protocol for neutron dosimetry and include the gamma-ray component of dose.

Animals↗
PubMed1987

A comparison of clinical and laboratory data on neutron therapy for locally advanced tumors.

Experimental results suggest advantages for neutrons where cells are hypoxic, in tumors which are slowly growing and also in a relative sparing of bone damage. The neutrons available at Hammersmith were of 7.5 MeV energy and produced a poorly penetrating beam, unsuitable for treating tumors in the pelvis and abdomen. Patients with locally advanced tumors in superficial sites were therefore selected to assess the effects of neutrons on normal and malignant tissues. One hundred and eight-nine patients had between them 191 locally advanced (T4 N0-3) tumors in the oral cavity, paranasal sinuses, salivary glands, and breast. Neutron therapy resulted in complete regression in 84% of which 13% subsequently recurred. Median survival for the whole group was 32 months. Twenty-eight other patients had advanced tumors of the head and neck which were recurrent after X ray therapy and other treatments; 82% of these completely regressed for more than 1 year. Complications appeared in 27% of patients not previously treated and in 46% who had already undergone X ray therapy. Seventy-four per cent of complications started in the skin. With neutrons of this energy there is minimal sparing of the skin and uneven distribution of dose resulting in "hot" spots. These affected skin, subcutis, and muscle. The high rates of control in these large tumors, the low incidence of bone necrosis, and the repair of some bones eroded by tumor correlate well with the experimental data. There was rapid regression of the tumor and close correlation between early and late effects on skin and subcutis. These two observations may relate to the fractionation, total dose, and overall time of treatment of 1560 cGy neutron dose given in 12 fractions over 28 days.

Breast Neoplasms↗
PubMed1987

Fast neutrons in the treatment of locally advanced breast cancer.

The clinical investigation of fast neutrons at Hammersmith Hospital included 17 patients who between them had 20 T4 breast cancers. The majority of these tumours were ulcerated and all were painful. Ten had recurred after multiple other therapies. Complete local regression was achieved in all but one (95%) and no tumour recurred. Symptoms were relieved in all cases. Median survival was 26 months. Three patients developed small areas of skin necrosis following trauma of previous radiation. All the neutron treated breasts became fibrosed, but this was painless. Neutron treatment needed only 12 attendances over 28 days, in contrast to the best results from photon therapy which required 6-7 weeks followed by implant of radioactive wire and/or surgical excision. One patient who had bilateral tumours received neutrons to the left breast and X-ray therapy (photons) to the right. The photon treated tumour did not completely regress and recurred. The neutron treated one completely regressed and did not recur. Neutrons were also more effective than tamoxifen which causes complete regression in only about 30% of cases. It is suggested that neutron therapy is indicated for locally advanced tumours which do not respond to hormones. Since metastases were a common cause of death, there remains a need for an effective adjuvant treatment, acceptable to elderly patients.

Adult↗
PubMed1986

Prospects for the application of fast neutrons in cancer therapy. Radiobiological bases and survey of the clinical data.

The rationale for introducing fast neutrons in therapy initially was a reduction in the Oxygen Enhancement Ratio (OER). The recent radiobiological developments indicate that, more generally, fast neutrons tend to reduce the difference in radiosensitivity between cell lines, or related to the degree of oxygenation (Oxygen Gain Factor), the position of the cells in the mitotic cycle (Kinetics Gain Factor), etc. The reduction of the differences in radiosensitivity brings a benefit for certain types of tumours (normally resistant to photons), but a disadvantage for other types of tumours (those which can currently be controlled by photon treatment). A review of the available clinical data is presented. The tumour types or sites for which a benefit has been observed are discussed: locally advanced tumours of the salivary glands, paranasal sinuses, some tumours of the head and neck area with metastatic lymph nodes, slowly growing, well differentiated soft tissue sarcomas, inoperable/recurrent melanomas, locally extended (C, D1) prostatic adenocarcinomas. Selection of the patients suitable for neutron therapy remains the main problem. Collaboration between neutron therapy centres is essential to accelerate the acquisition of sufficient clinical data needed in order to improve patient selection, as well as the optimum modality of application of fast neutrons.

Energy Transfer↗
PubMed1985

The 8 MeV linear accelerator at the MRC Cyclotron Unit, Hammersmith Hospital, London.

This machine was the first linear accelerator designed for medical use and the first to be installed in a hospital. The first patient was treated in 1953 and the last in 1969. During this period the machine was used for research during the evenings and latterly it was available for research all day long. It was switched off for the last time in February 1984. In addition to the X-ray beam, electrons were used for treatment and for research, where the high dose rate and large field size were particularly useful. An account is given of some of the highlights of the clinical and research programmes.

Animals↗
PubMed1984

New neutron sources for radiotherapy.

All existing neutron sources suffer from disadvantages which would not be tolerated in modern megavoltage X-ray equipment. Experimental work with 30-60 MeV protons on beryllium and other elements has shown how these difficulties can to a large extent be overcome. Angular distributions and kerma rates as a function of proton energy are presented for various targets. Thin targets are found to be a better method than filtration for improving the penetration of the beam. A 237Np fission counter and a GM counter have been used to decompose stray radiation into its neutron and gamma-ray components. A model of a treatment head was found to attenuate the neutron component to less than 1% of its value in the useful beam.

Beryllium↗
PubMed1982

Practical problems in neutron dosimetry.

The first problem discussed is the best phantom material. It is argued that tissue composition has a greater effect on dose distributions from photons than on those from neutrons. As water is normally used for photons, it should be satisfactory for neutrons, but checks are needed with high-energy neutron beams. Another serious problem is that of kerma ratios for neutrons above 20 MeV where highly discordant values have been calculated by several authors. Finally some suggestions are made about measurement of the gamma-ray component in beams of high-energy neutrons.

Europe↗