CONFIRMATION OF TARGET LOCALIZATION AND DOSIMETRY FOR 3D CONFORMAL RADIOTHERAPY TREATMENT PLANNING BY MR-IMAGING OF A FERROUS SULFATE GEL HEAD PHANTOM

A detailed methodology has been developed to verify the three-dimensio nal (3D) radiation dose mapping of conformal therapy radiation treatme nt planning by FeMRI dosimetry. A phantom that consisted of a human sk ull filled with a 1-mM solution of ferrous sulfate and 0.1-N sulfuric acid gelled with 7.5% (by weight) gelatin was employed. With a spheric al target volume in the head phantom, five noncoplanar conformal beams were designed through the use of a 3D treatment planning system devel oped in-house. The phantom was irradiated with a 6-MV linear accelerat or to a total dose of 25 Gy delivered to the periphery of the target v olume. The phantom and a set of calibration vials were scanned simulta neously in a GE 1.5T MR imager with six different multiscan inversion- recovery pulse sequences. The values of T-1 were evaluated on a pixel- by-pixel basis through the use of custom-built software on a UNIX work station and were converted to dose using calibration data. Comparisons of dose distributions between those measured by FeMRI and those calcu lated by 3D treatment planning show good agreement.