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Biomedical subjects

A T Redpath

Publications and source records attributed to A T Redpath.

12 recordsLinked to original sources
PubMed1992

A multidisciplinary approach to improving the quality of tangential chest wall and breast irradiation for carcinoma of the breast.

Physicists, radiotherapists and radiographers have worked together to enhance the quality and accuracy of radiotherapy for tangential irradiation of the chest wall and breast. Each stage of the process has been reassessed and improved. A technique has been developed on the treatment simulator which determines the required beam directions and sizes in a straightforward manner. A computerised tomography facility has also been developed on the simulator and this provides one or more slices for planning through the treatment volume, thus allowing accurate determination of external contour and lung position with the patient in the treatment position. The beam edge entry points and the isocentre position can be seen from radiation opaque markers placed on the skin surface, allowing accurate reproduction of the treatment beam positions as set on the simulator. A photon beam algorithm that corrects for the changes in scatter dose in a 3-dimensional (3-D) inhomogeneous situation has been developed and applied to tangential chest wall irradiation. This has shown large differences (up to 10%) in dose compared to a conventional 2-dimensional algorithm. The changes in dose distribution due to the accurate determination of lung position have also been investigated. A method has been developed of measuring the volume of ipsilateral lung irradiated. Dose-area histograms are used to evaluate the fraction of the lung area irradiated in the central slice, and an estimate of the volume irradiated can be made using a beam's eye radiograph and the simulator CT image.

Algorithms↗
PubMed1992

Stage IB cervical carcinoma: a clinical audit.

All patients with FIGO Stage IB cervical cancer registered with the Department of Clinical Oncology at the Western General Hospital, Edinburgh, during the 6 years from 1979 to 1984 have been reviewed, as part of a continuing programme of clinical audit. Of the 140 patients with Stage IB disease, 68 (49%) were treated by primary surgery of whom 44 (31%) also received adjuvant radiotherapy. Radical radiotherapy was the definitive treatment for 69 patients (49%). Three patients (2%) were not treated with curative intent. The crude 5-year survival rate for all cases was 72% and the cause-specific 5-year survival rate was 78%. Local tumour control at 5 years was 72%. There was no significant difference in outcome between the surgically treated and irradiated groups of patients. Age, histology and nodal status did not influence outcome. Irradiated patients with bulky tumours fared significantly worse than the other patients who received radical radiotherapy. Multivariate analysis of all patients revealed no significant independent prognostic variables. Primary surgery appears to confer no benefit over radical radiotherapy in terms of either survival or local control. Treatment-related late bladder and bowel morbidity was, however, significantly worse in irradiated patients.

Adult↗
PubMed1991

Lung CT density correlates with measurements of airflow limitation and the diffusing capacity.

We studied 80 subjects (63 M, 17 F; 23-82 yrs) and related lung computerized tomography (CT) density with age, height, spirometry, lung volumes, diffusing capacity and arterial blood gas tensions. These subjects demonstrated a wide range of physiological impairment (forced expiratory volume in one second (FEV1) 8-116% predicted; diffusing capacity (Kco) 15-139% predicted; arterial oxygen tension (Pao2) 38-91 mmHg). They ranged from normal subjects to patients with chronic respiratory failure. Lung density was derived from CT density histograms measured as both mean Emergency Medical Information (EMI) number (EMI scale: 0 = water, -500 = air, EMI number of normal lung tissue range approximately -200 to -450) and the lowest 5th percentile EMI number, the latter value being more likely to represent the density of lung parenchyma. Lung CT density correlated most strongly with airflow obstruction (EMI 5th percentile versus FEV1/forced vital capacity (FVC) % predicted, r = 0.73, p less than 0.001) and diffusing capacity (EMI 5th percentile versus Kco, r = 0.77, p less than 0.001). This suggests that reduction in lung density, which reflects loss of the surface area of the distal airspaces, is a major index of respiratory function in patients with smoking related chronic obstructive pulmonary disease (COPD). These data provide no indication of other factors such as small and large airways disease, and loss of elastic recoil, which may contribute to airflow limitation, or disruption of the pulmonary vascular bed which may also affect CT lung density.

Adult↗
PubMed1985

The use of an image processing system in radiotherapy simulation.

Image quality produced in radiotherapy simulation is often so poor in certain anatomical sites (e.g. the pelvis) that it can adversely affect clinical judgement with regard to treatment set-up. In treatment planning both the field arrangement and the availability of accurate anatomical information are important, and should ideally be provided at the time of simulation by methods based on the principle of computerised tomography. In this work an image processing system has been used as a link between the video output from the simulator and the treatment planning computer in order to implement a CT facility on the simulator, as well as allowing real-time image enhancement to be investigated as a method of improving picture quality. This approach also enables a new method of simulation to be considered which reduces patient dose and prolongs the useful working life of the X-ray tube.

Humans↗
PubMed1977

Radiation osteitis following irradiation for breast cancer.

Radiographs of the shoulder girdle were examined in 180 women who attended the breast follow-up clinic at the Department of Radiotherapy, Edinburgh. These comprised 52 controls who had been treated by radical mastectomy alone and 128 patients who had received post-operative X-ray therapy. The significance of osteoporosis as a sequel to irradiation is doubtful as it occurred in a substantial proportion of the control cases. Osteitis of severe degree occurred in 13.3% of patients who had been irradiated and was present in a mild form in a further 8.6%. The development of severe osteitis requires an NSD of 1650 rets or more. Estimates of the frequency of radiation osteitis are of no value unless detailed information is also provided about the techniques and quality of radiation.

Aged↗
PubMed1977

A comprehensive radiotherapy planning system implemented in Fortran on a small interactive computer.

A suite of Fortran programs for carrying out the various dose computational aspects of radiotherapy has been developed on an enhanced RAD8 computing system. The hardward configuration of the computer is described and the main features of the programs in the suite are discussed. The include: (a) beam data input systems for use with linear accelerators and cobalt units; (b) static and rotational teletherapy planning, with computer optimization in the static planning; (c) irregular field calculations with isodose visualization; (d) interstitial calculations including routines which will reconstruct a radium needle implant in three dimensions in addition to presenting the isodose distribution in any desired plane. The problems of implementing the programs on another computer system are discussed.

Computers↗
PubMed1977

The reconstruction and dose-rate calculation of radium needle implants.

A comprehensive computer program has been developed for carrying out the various tasks associated with radium needle implants. Data input for the program are obtained by digitizing an orthogonal pair of radiographs with an analogue tracing system. Corresponding needles in the two radiographs are automatically located, and the implant may be rotated to any desired position in three dimensional space, at the same time presenting a view of the rotation on a storage oscilloscope. Automatic determination of the mean plane of a planar implant is possible, and the dose-rate distribution may be calculated in any specified plane. A Paterson--Parker exposure rate calculation may be performed with a biological dose and treatment time correction incorporated. The program is written in Fortran and runs on a small interactive computer system.

Computers↗
PubMed1976

A new technique for radiotherapy planning using quadratic programming.

Previous attempts at optimization of radiotherapy planning are described and criticized, and consideration of these attempts has resulted in the development of a new technique using quadratic programming. Uniformity of tumour dose is selected as the most important feature of any plan, and this is achieved by minimizing the variance of the dose to preselected points within the tumour. The dose to vulnerable regions can be constrained not to exceed a given percentage of the mean tumour dose. Optimization of field weight and field type is possible. The operation of the system is described and some typical results are given.

Humans↗
PubMed1975

A set of fortran subroutines for optimizing radiotherapy plans.

Quadratic Programming techniques have been applied to the optimization of radiation field weighting in Radiotherapy planning. Wedge selection has also been included by means of an exhaustive search. The radiation dose at any point in the patient may be constrained to be less than a stated percentage of the tumour dose. The routines have been successfully interfaced into a small computer interactive planning system, but they could represent an even more powerful tool in batch and time sharing systems. Minimum operator intervention is required in their use.

Computers↗
PubMed1975

Rapid depth dose determination by a computer-controlled dosimetry system.

A comprehensive depth dose measuring system controlled by a small computer has been designed to enable full depth dose information for a linear accelerator to be obtained within one day. An ionization microchamber is moved rapidly under computer control in a horizontal plane to preselected points within a water phantom by two stepping motors to a spatial resolution of 0-025 mm. The ionization current pulses are converted to DC voltages by an interface providing complete charge integration and yet having a rapid response to drastic changes in dose level. These are fed to the computer for analysis and subsequent conversion to depth dose data. The chamber path follows a preselected fan-shaped grid after automatic determination of the X-ray beam central axis. The combination of rapid chamber motion with halts for charge integration and computer sampling has resulted in fast data acquisition independent of measurement response times. This information, which is stored on disc, can be directly read by a treatment planning program. The overall accuracy of measurement lies within 0-5% of the true depth dose at any point. Central axis and transverse profiles can be assessed at the time of measurement through visualization on the computer storage oscilloscope.

Computers↗