PURPOSE: To determine the prostate volumes defined by using MRI and CT scans, as well as the difference between prostate delineation in MRI and CT in three dimensions (3D). A further goal was to use MRI to identify subgroups of @entity1 in whom seminal vesicle irradiation can be avoided. METHODS AND MATERIALS: A total of 294 @entity1 with biopsy-proven @entity263 (MRI stages: T(1), 16 [5%]; T(2), 84 [29%]; T(3), 191 [65%]; T(4), 3 [1%]) underwent pelvic CT and MRI scans before intensity-modulated radiation therapy (IMRT) planning. 3D images were used to compare the prostate volumes defined by superimposed MR and CT images. Prostate volumes were calculated in cm(3). RESULTS: The mean prostate volume defined by MRI (44.3 cm(3) [range, 8.8-182.8 cm(3)]) was 35% smaller than that defined by CT (68.5 cm(3) [range, 15.2-241.3 cm(3)]). The areas of nonagreement were observed predominantly in the most superior and inferior portions of the prostate. The incidence of @entity3 ( @entity3 ) identified by MRI was 63% (n = 182 of 290). The median length of @entity3 was 2.6 cm (range, 1.1-4.7 cm; 62% of the median SV length). The low-risk @entity1 (59%, n = 171 of 290) calculated by applying the Roach and Diaz formula had a @entity3 rate of 57% (n = 97 of 171), the high-risk @entity1 (41%, n = 119 of 290) of 71% (n = 85 of 119). CONCLUSIONS: Compared with MRI, CT scans overestimate prostate volume by 35%. CT-MRI image fusion-based treatment planning allows more accurate prediction of the correct staging and more precise target volume identification in @entity263 @entity1 .

Definition of the CTV prostate in CT and MRI by using CT-MRI image fusion in IMRT planning for XXXX .

@entity1 :: ('9606', 'Species') :: ['patients'] @entity263 :: ('MESH:D011471', 'Disease') :: ['prostate cancer'] @entity3 :: ('MESH:D009362', 'Disease') :: ['SVI', 'seminal vesicle invasion']
@entity263 :: (MESH:D011471,Disease) :: ['prostate cancer']
