The microdosimetric study of the dose mean lineal energy shows that radiation quality changes in the contrast-medium-labelled region compared to homogeneous tissue are fairly small and limited to 10%. An attempt to optimize the irradiation scheme is discussed. It is shown that the dose enhancement in tumours can be highly significant (up to about sixfold for realistic 80-120 kVp x-ray spectra and an iodine concentration of 50 mg ml-1) but that dose homogeneity in the tumour depends on photon energy, contrast-medium concentration and type, and irradiation scheme. Two idealized patient treatment plans (head and lung) for irradiation with CT-arc beams were calculated. In this work, we have investigated the dosimetric and microdosimetric characteristics of kV contrast-enhanced radiation therapy (CERT) for different photon energies, contrast-medium concentrations and types (I and Gd). This causes a significant dose enhancement to the tumour by exploiting the high cross sections for the photo-electric effect for kV x-rays.
This picture could change drastically when tumours can be labelled with contrast medium, containing high atomic number elements. Kilovolt x-rays are clearly suboptimal compared to MV photon beams for radiotherapy of deep-seated tumours because of the increased attenuation in tissue, causing a rapid dose fall-off.
0 kommentar(er)
