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Biomedical subjects

P C Williams

Publications and source records attributed to P C Williams.

8 recordsLinked to original sources
PubMed1992

A dosimetric intercomparison of megavoltage photon beams in UK radiotherapy centres.

A dosimetry intercomparison has been carried out for all 64 radiotherapy centres in the UK. Doses were measured with an ionization chamber in an epoxy resin water-substitute phantom of relatively simple geometry. Reference-point measurements were made for all MV photon beams. For 61 Co-60 beams, a mean ratio of measured-to-stated dose of 1.002 was observed with a standard deviation of 0.014, whilst for 100 MV x-ray beams, the corresponding figures were 1.003 and 0.015. 97% of beams lay within a +/- 3% deviation. One measurement was instrumental in discovering a large discrepancy. Doses were also investigated in two planned three-field distributions at one beam quality in each centre. One of these was in a homogeneous phantom, whilst the second included a lung-equivalent insert. Doses were measured at the central point and at four other points in the high dose volume. In both situations, the mean ratio of measured-to-calculated doses for all points was 1.008, with standard deviations of 0.027 and 0.035 for the uniform and non-uniform phantoms, respectively. Discrepancies over 5% were followed up. The work must be viewed in the context of other international intercomparisons and is an essential part of wider radiotherapy audit processes.

Humans↗
PubMed1992

Computer-assisted generation of multi-leaf collimator settings for conformation therapy.

Techniques for the automatic set up of the individual leaf positions of a Philips multi-leaf collimator system to cover a defined target volume are described. Tumour outline data for multi-field treatments may be obtained from one of two techniques, either from simulator images or from cross-sectional computed tomography (CT) slices. In the first technique, simulator images are digitized directly from image intensifier video signals or from conventional film radiographs using a CCD camera. Corrections for image distortion are carried out before reformatting the digitized images to a common data structure. Target outlines are subsequently traced interactively on the digital image to create an outline file. In the second technique, target volumes are defined on several individual CT slices and these are then used to obtain projected graphical views from any desired angle. In both techniques, a scaled graphical representation of leaf positions is then displayed and set relative to the outer edge of the target outline. Both techniques allow interactive repositioning of single leaves when required, or the operator can specify a margin around the projected target volume. Leaf prescription data files are created and are transferred via a Decnet-OSI-Opennet network link to an Intel microcomputer, which is used to drive the device itself. Examples of both techniques are given.

Humans↗
PubMed1979

Evaluation of the efficacy and safety of guanabenz versus clonidine.

The antihypertensive efficacy and safety of guanabenz were evaluated against clonidine in two groups of 18 patients with uncomplicated essential hypertension. Both compounds reduced systolic and diastolic blood pressure at the doses used, whether pressures were measured in the supine or standing positions. Side-effects, such as dry mouth and drowsiness, were similar in both groups of patients. No postural hypotension occurred.

Adult↗
PubMed1979

Aldactone and acebutolol in treatment of hypertension.

Twenty-one essential hypertensives were randomly treated with Aldactone, acebutolol or a combination of the two drugs. Statistically significant falls in systolic and diastolic pressures were demonstrated during treatment with Aldactone 100 mg daily, also when acebutolol and Aldactone 200 mg daily were administered. When the combination of Aldactone and acebutolol was given, diastolic pressures were lowered to a greater degree than seen with individual treatments.

Acebutolol↗
PubMed1979

Whole body electron therapy in mycosis fungoides--a successful translational technique achieved by modification of an established linear accelerator.

A translational technique, adapting an established MEL SL75/10 linear accelerator, which gives a satisfactory physical and clinical 3 MeV whole-body electron treatment in mycosis fungoides is described. Tolerance of the patients proved excellent and 16 out of 21 achieved satisfactory remission of the disease. In spite of delivering significant skin doses it was possible to re-treat two relapsing patients without complications and with clinical success.

Adult↗
PubMed1978

Treatment of hypertension with single daily doses of acebutolol.

The efficacy of single daily doses of acebutolol, alone or combined with chlorexolone, was investigated in a group of 20 ambulant patients with uncomplicated hypertension of mild-to-moderate severity. severity. Patients were seen at fort-nightly intervals when doses were adjusted. Blood pressure was measured in all instances at 2 and 8 hours after medication, and after it had stabilized, at 26 hours after the last dose. The results indicate that a single dose of acebutolol alone produces significant lowering of supine and erect blood pressures for 24 hours (P less than 0,005). Combining chlorexolone with acebutolol does not improve the hypotensive effect of the beta-blocker significantly, but makes a smaller dose effective.

Acebutolol↗