A method for 3D imaging of absorbed dose in 3D radiotherapy

M. CARRARA G. GAMBARINI S. GAY L. PIROLA AND M. VALENTE*,?

Milano, Italia

Jornada; Annual Report Congress University of Milan; 2005

One of the major necessities that appear with the continuum development of conformal radiotherapies is a corresponding improvement of dosimetry techniques. A method has been set up for prompt imaging of absorbed dose in tissue-equivalent phantoms, with the possibility of 3D reconstruction of the spatial dose distribution, with millimetric resolution. The phantoms, acting by themselves as continuous dosimeters, are obtained by incorporating a chemical dosimeter into a tissue-equivalent gel matrix. The chemical dosimeter is a ferrous sulphate solution (which is the main component of the standard Fricke dosimeter) in which ionizing radiation produces oxidation of ferrous ions Fe2+ into ferric ions Fe3+. Initially, the imaging of Fricke-infused gel was performed by means of magnetic resonance analyzers, owing to the different reduction of the relaxation times of hydrogen nuclei caused by ferrous and ferric ions. Afterwards, the metal ion indicator xylenol orange (XO) was added to the dosimeter composition. The complex that XO forms with ferric ions causes visible-light absorption, centred at about 585 nm, in amount linearly correlated to the absorbed dose. A suitable imaging technique was then developed, based on the analysis of visible light transmittance through gel layers. The spatial distribution of absorbed dose is obtained from optical absorbance images, detected by means of a CCD camera provided with suitable filter around 585 nm [1]. Wide software was properly developed using the Matlab® program [2], able to carry out all the manipulations necessary to get the interactive rendering of 3D dose distribution, starting from a set of acquired dosimeters? images. In order to check the reliability of the method, phantom exposures in standard configurations were performed and the dose profiles extracted from images were compared with the results obtained by means of conventional dosimeters, such as ionisation chambers [3], and with Monte Carlo calculations. Fricke-infused gel was performed by means of magnetic resonance analyzers, owing to the different reduction of the relaxation times of hydrogen nuclei caused by ferrous and ferric ions. Afterwards, the metal ion indicator xylenol orange (XO) was added to the dosimeter composition. The complex that XO forms with ferric ions causes visible-light absorption, centred at about 585 nm, in amount linearly correlated to the absorbed dose. A suitable imaging technique was then developed, based on the analysis of visible light transmittance through gel layers. The spatial distribution of absorbed dose is obtained from optical absorbance images, detected by means of a CCD camera provided with suitable filter around 585 nm [1]. Wide software was properly developed using the Matlab® program [2], able to carry out all the manipulations necessary to get the interactive rendering of 3D dose distribution, starting from a set of acquired dosimeters? images. In order to check the reliability of the method, phantom exposures in standard configurations were performed and the dose profiles extracted from images were compared with the results obtained by means of conventional dosimeters, such as ionisation chambers [3], and with Monte Carlo calculations. 2+ into ferric ions Fe3+. Initially, the imaging of Fricke-infused gel was performed by means of magnetic resonance analyzers, owing to the different reduction of the relaxation times of hydrogen nuclei caused by ferrous and ferric ions. Afterwards, the metal ion indicator xylenol orange (XO) was added to the dosimeter composition. The complex that XO forms with ferric ions causes visible-light absorption, centred at about 585 nm, in amount linearly correlated to the absorbed dose. A suitable imaging technique was then developed, based on the analysis of visible light transmittance through gel layers. The spatial distribution of absorbed dose is obtained from optical absorbance images, detected by means of a CCD camera provided with suitable filter around 585 nm [1]. Wide software was properly developed using the Matlab® program [2], able to carry out all the manipulations necessary to get the interactive rendering of 3D dose distribution, starting from a set of acquired dosimeters? images. In order to check the reliability of the method, phantom exposures in standard configurations were performed and the dose profiles extracted from images were compared with the results obtained by means of conventional dosimeters, such as ionisation chambers [3], and with Monte Carlo calculations.