Search

The objective of the dynamic radiotherapy project 'Dynarad' within the European Community has been to compare and grade treatment techniques that are currently applied or being developed at the participating institutions. Cervical cancer was selected as the tumour site on the grounds that the involved organs at risk, mainly the rectum and the bladder, are very close to the tumour and partly located inside the internal target volume. In this work, a solid phantom simulating the pelvic anatomy was used by institutions in Belgium, France, Greece, Holland, Italy, Sweden and the United Kingdom. The results were evaluated using both biological and physical criteria. The main purpose of this parallel evaluation is to test the value of biological and physical evaluations in comparing treatment techniques. It is demonstrated that the biological objective functions allow a much higher conformality and a more clinically relevant scoring of the outcome. Often external beam treatment techniques have to be combined with intracavitary therapy to give clinically acceptable results. However, recent developments can reduce or even eliminate this need by delivering more conformal dose distributions using intensity modulated external dose delivery. In these cases the reliability of the patient set-up procedure becomes critical for the effectiveness of the treatment.

The energy dependence of the luminance ratio due to scattered and primary radiation has been determined for four types of X-ray intensifying screens. A water phantom of 30 cm X 30 cm X 20 cm was used as the scattering medium. Ten narrow band X-ray spectra were used as incident radiation: the mean energies of these spectra ranged from 28 to 84 keV. Using the monoenergetic data, results were calculated for broad spectra and compared with measured results for broad spectra. For tube voltages up to 50 kV the calculated results agreed well with the measured results: for higher tube voltages a small difference occurred.

A computer program was developed to calculate both integral absorbed dose in a water phantom and entrance exposure, for the imaging of iodine contrast with x-ray intensifying screens. The effect of filtration of the x-ray beam on integral absorbed dose and entrance exposure was studied for 27 different filter materials and four types of intensifying screens. The dose and exposure were calculated, keeping the image contrast and energy absorption in the screens constant. To check the validity of the calculations, a number of measurements were performed, the results of which agreed well with our calculations. A remarkable result is that dose and exposure reduction can be achieved almost equally well with conventional filters (aluminum and copper) as with a number of K-edge filters. This was found for situations commonly encountered in diagnostic radiology (60-80 kV, 20 cm water). This finding is in contrast to a number of earlier studies, in which K-edge filters were found to be superior to conventional filters.