Biopsy protocol stability in a three-dimensional model of prostate cancer:Changes in cancer yield after adjustment of biopsy positions

Objectives. Transrectal ultrasound-guided prostate biopsies are often taken according to a systematic, standardized schedule. The diagnostic stability of this system was evaluated by moving the biopsies in a three-dimensional (3D) model. Methods. A computerized 3D reconstruction was made from each of 75 radical prostatectomy specimens. Simulated core biopsies imitated a standardized 10 -biopsy protocol, including sextant biopsies. In total, 30,000 biopsies wer e generated by moving the standardized biopsies 1, 2, 3, and 4 mm (parallel needle shifts) or 5 degrees, 10 degrees, 15 degrees, and 20 degrees (rotat ion of the needle tip) in a random direction. Results. The diagnosis of the individual biopsy changed from cancer to beni gn or vice versa in 4.9% to 15.7% after 1 to 4-mm parallel needle shifts an d 2.0% to 7.5% after 5 degrees to 20 degrees rotations. The corresponding f igures for the final diagnosis of the 10-biopsy set were 0.8% to 9.6% and 0 .5% to 3.2%. Transition zone biopsies containing cancer changed to benign m ore often than the other biopsies (P <0.001). Parallel needle shifts of 2 m m changed the diagnosis more often than the 15 degrees rotation (9.4% and 5 .9%, respectively, P <0.001), although conveying the same overall needle sh ift. Conclusions. The cancer yield of prostate biopsies is influenced even by sm all changes in needle positions. The transition zone biopsies are most like ly to change from cancer to benign when moved. Changing the insertion point of the needle has a higher impact on cancer yield than rotating the tip. U ROLOGY 54: 862-868, 1999. (C) 1999, Elsevier Science Inc.