A simple isocenter checking procedure for radiotherapy treatment machines using the optical pointer.

Techniques are described for simple and convenient checks on the position and size of the isocenter of radiotherapy treatment machines by measuring the displacement of the optical pointer on a flat scale on the surface of the treatment couch.

Techniques for intraoral electron treatments.

The use and the positioning of intraoral electron applicators is reviewed. It is concluded that there are clear advantages in the use of a treatment shell that carries a mounting and allows the electron applicator to be firmly held in position, without a bite block.

The computer analysis of interstitial implants in radiotherapy.

The use of computer techniques in the analysis of needle implants in Radiotherapy treatment is assessed from the point of view of the end user. The specification of a routine approach to the analysis is developed so that consistent assessments of implants will be possible to permit the accumulation of dosimetry data for correlation with clinical outcome. The protocol, in summary, consists of the identification of the plane in which the implant lies and of the presentation of dose rate information in the form of standardised isodose contours through three transverse slices at right angles to the "plane of lie". These transverse slices have been selected at the averaged centre of the sources (the "central plane" of Pierquin et al. [14] and at 5 mm distance from the averaged proximal and distal active ends of the sources. The isodose contours chosen for presentation include two "reference dose" contours representing 85 and 127% of the minimum dose rate found in the central plane for prescription calculation purposes and a limited set of standard contours for assessment of homogeneity of dose rate and for comparative purposes. A minimum number of subsidiary display planes may be used to characterise the implant when necessary, a lateral plane commonly proving useful. The position of the chosen sections may with value be shown on the X-ray films. A method of orientating the display with respect to anatomical structures by super-imposing on the isodose display a frame-like projection whose sides relate to anatomical landmarks is demonstrated. The future extension of the analysis to a fully automated approach is discussed.

Radiotherapy treatment planning for patients fitted with prostheses.

The effects of prostheses on radiotherapy treatment planning are discussed. The compositions of commonly used materials are tabulated. Sample plots show the size of perturbations produced by typical absorbers at 8 MV. A technique for estimating the density of a prosthesis in a patient is demonstrated and the effects of prostheses on representative radiotherapy plans are illustrated.

Interstitial radiation therapeutic techniques at Mount Vernon Hospital.

Retrospective analysis of 56 cases of carcinoma on the lateral border of the anterior two thirds of the tongue treated at Mount Vernon Hospital using radium needle implant alone yielded 5-year actuarial survivals of 75.3 per cent in 25 T1N0 cases and 81.8 per cent in 25 T2N0 cases. Five-year actuarial local recurrence of 17.5 per cent was recorded in the T1 group and 35 per cent in the T2 group. Local recurrences were attributed to failure of the implant to encompass extensions of the tumour along the lateral border or into the musculature of the tongue. Five-year actuarial local recurrence of 66.2 per cent was recorded in 18 patients with carcinoma of the breast treated by radium needle implant alone; 4 of these 9 local recurrences occurred at some distance from the treated area and could not be classed as marginal recurrences. A preliminary investigation carried out in 1981 indicated that significant improvements in source distribution, particularly at poorly accessible sites, could be achieved using afterloading techniques. In addition the use of 192Ir as a source could result in improvements in staff protection.

Tumour uptake of thallium-201 chloride.

The uptake of 201Tl-chloride in tumours has recently been investigated in several authors' laboratories. We are reporting studies on the uptake in malignant melanoma in mice. Generally, we confirm the published data qualitatively in finding higher uptake in tumour than in muscles. We confirm the rapid blood clearance and high kidney concentration, but we did not measure the myocardial uptake. We observed the concentrations in kidney muscle and tumour to rise during the first four hours while that in the liver fell from one hour onwards. We did not observe markedly higher uptake in melanin rich tumour than in other tumours.

Performance characteristics of a gamma camera over a wide range of energies.

The problem of choosing which collimator to use for imaging a new isotope has been approached by collecting resolution and sensitivity data for a selected group of isotopes. These have been chosen to be readily available and to have generally a single gamma-ray only. Resolution and sensitivity plots for a low energy collimator and a high energy collimator are presented and their use with several isotopes of interest is discussed. The interpretation of recommedations in the literature on the choice of collimators for newly introduced isotopes would be considerably simpler if data in this format were commonly available.