title: Dosimetric and microdosimetric study of contrast-enhanced radiotherapy with kilovolt x-rays.
abstract: 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. This picture could change drastically when tumours can be labelled with contrast medium, containing high atomic number elements. This causes a significant dose enhancement to the tumour by exploiting the high cross sections for the photo-electric effect for kV x-rays. 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). Two idealized patient treatment plans (head and lung) for irradiation with CT-arc beams were calculated. 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. An attempt to optimize the irradiation scheme is discussed. 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%. It is concluded that kV-CERT is a promising radiotherapy technique, provided contrast medium can be delivered reliably to tumours.
authors: Medical Physics Department, McGill University Health Centre, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Québec, H3G 1A4, Canada. fverhaegen@medphys.mcgill.ca
authors: Frank
authors: F
authors: Verhaegen
authors: Brigitte
authors: B
authors: Reniers
authors: François
authors: F
authors: Deblois
authors: Slobodan
authors: S
authors: Devic
authors: Jan
authors: J
authors: Seuntjens
authors: Dimitre
authors: D
authors: Hristov
mesh_terms: D001822:Body Burden; D003198:Computer Simulation; D003287:Contrast Media / Q000627:therapeutic use*; D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness; D016896:Treatment Outcome; D014964:X-Ray Therapy / Q000379:methods*
chemical_list: D003287:Contrast Media