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Biopsy protocol stability in a three-dimensional model of prostate cancer: changes in cancer yield after adjustment
L Egevad1, H Frimmel, S Mattson
1Department of Pathology, Centre of Image Analysis, Uppsala University, Sweden.
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 were 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(rotation of the needle tip) in a random direction.
Results:
The diagnosis of the individual biopsy changed from cancer to benign or vice versa in 4.9% to 1 5.7% after 1 to 4-mm parallel needle shifts and 2.0% to 7.5% after 5 degrees to 20 degrees rotations. The corresponding figures 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 more often than the other biopsies (P <0.001). Parallel needle shifts of 2 mm 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 shift.
Conclusions:
The cancer yield of prostate biopsies is influenced even by small changes in needle positions. The transition zone biopsies are most likely 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.