The computer analysis of interstitial implants in radiotherapy

Abstract

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.