Characterizing the range of simulated prostate abnormalities palpable by digital rectal examination.

BACKGROUND Although the digital rectal exam (DRE) is a common method of screening for prostate cancer and other abnormalities, the limits of ability to perform this hands-on exam are unknown. Perceptible limits are a function of the size, depth, and hardness of abnormalities within a given prostate stiffness. METHODS To better understand the perceptible limits of the DRE, we conducted a psychophysical study with 18 participants using a custom-built apparatus to simulate prostate tissue and abnormalities of varying size, depth, and hardness. Utilizing a modified version of the psychophysical method of constant stimuli, we uncovered thresholds of absolute detection and variance in ability between examiners. RESULTS Within silicone-elastomers that mimic normal prostate tissue (21kPa), abnormalities of 4mm diameter (20mm(3) volume) and greater were consistently detectable (above 75% of the time) but only at a depth of 5mm. Abnormalities located in simulated tissue of greater stiffness (82kPa) had to be twice that volume (5mm diameter, 40mm(3) volume) to be detectable at the same rate. CONCLUSIONS This study finds that the size and depth of abnormalities most influence detectability, while the relative stiffness between abnormalities and substrate also affects detectability for some size/depth combinations. While limits identified here are obtained for idealized substrates, this work is useful for informing the development of training and allowing clinicians to set expectations on performance.