A rotate–translate CT scanner providing cross‐sectional data suitable for planning the dosimetry of radiotherapy treatment

Abstract

An isotope scanner (J and P Engineering Multipoise scanner, Mk. III) was converted to provide a simple transmission CT [computed tmogratomography] scanning device, using a 137Cs .gamma.-ray source. The performance of the scanning was evaluated by imaging a variety of phantoms and an anesthetized rabbit. The relationship between the measured linear attenuation coefficient and the known electron density was linear, for a range of materials with densities between those of bone and air. For reconstructed pixels of size 5 .times. 5 mm2 the percentage standard deviation of linear attenuation coefficient is typically 2.4% for bone and 3.6% for muscle. The spatial resolution of the device was measured and the performance of the scanner with the maximum design source strength was predicted. In the reconstruction of a cross section of the rabbit and of a human thorax phantom, air-muscle, lung-muscle, and muscle-bone interfaces are clearly visible. From experience gained with this scanner the role of simple CT scanning devices in radiotherapy treatment planning is considered. The resolution in linear attenuation coefficient and the spatial resolution available from the scanner are considered sufficient for radiotherapy treatment planning.