INITIAL CLINICAL-ASSESSMENT OF CT-MRI IMAGE FUSION SOFTWARE IN LOCALIZATION OF THE PROSTATE FOR 3D CONFORMAL RADIATION-THERAPY

Purpose: To assess the utility of image fusion software and compare MR T prostate localization with CT localization in patients undergoing 3D conformal radiation therapy of prostate cancer. Materials and Methods : After a phantom study was performed to ensure the accuracy of image fusion procedure, 22 prostate cancer patients had CT and MRI studies b efore the start of radiotherapy. Immobilization casts used during radi ation treatment were also used for both imaging studies. After the cli nical target volume (CTV) (prostate or prostate + seminal vesicles) wa s defined on CT, slices from the MRI study were reconstructed to preci sely match the CT slices by identifying three common bony landmarks on each study. The CTV was separately defined on the matched MRI slices. Data related to the size and location of the prostate were compared b etween CT and MRI. The spatial relationship between the tip of urethro gram cone on CT and prostate apex seen on MRI was also estimated. Resu lts: The phantom study showed the registration discrepancies between C T and MRI smaller than 1.0 mm in any pair in comparison. The patient s tudy showed a mean image registration error of 0.9 (+/-0.6) mm. The av erage prostate volume was 63.0 (+/-25.8) cm(3) and 50.9 (+/-22.9) cm(3 ) determined by CT and MRT, respectively. The difference in prostate l ocation with the two studies usually differed at the base and at the a pex of the prostate. On the transverse MRT, the prostate apex was situ ated 7.1 (+/-4.5) mm dorsal and 15.1 (+/-4.0) mm cephalad to the tip o f urethrogram cone. Conclusions: CT-MRI image fusion study made it pos sible to compare the two modalities directly. MRI localization of the prostate is more accurate than CT, and indicates the distance from con e to apex is 15 mm. CT-MRI image fusion technique provides valuable su pplements to CT technology for more precise targeting of the prostate cancer. (C) 1997 Elsevier Science Inc.