Han and Stoianovici: Making biopsies more accurate with a new Prostate Coordinate System.
Doctors performing a needle biopsy of the prostate do the best they can, but they’re the first to tell patients that it’s not perfect. Although these biopsies are guided by transrectal ultrasound, they’re still "freehand." This means that "the cores are often clustered, they miss regions, and they do not precisely follow the intended template," says Dan Stoianovici, Ph.D., Director of the Urology Robotics Program. "Biopsy targeting errors are on the order of 9 millimeters – too high to reliably find a clinically significant tumor in the prostate."
"There are many reasons why
needle biopsies miss cancer,
including errors in execution –
aiming for one part of the prostate
but not hitting it."
Director of the Urology Robotics Program. "Biopsy targeting errors are on the order of 9 millimeters – too high to reliably find a clinically significant tumor in the prostate." There are many reasons why needle biopsies miss cancer, including errors in execution – aiming for one part of the prostate but not hitting it – and problems with the imaging. But Stoianovici believes that one big problem is the lack of a good map – a "general, commonly accepted system to define a prostate location precisely and accurately." Instead, biopsy samples are usually taken from regions of the prostate, "but these are not assigned relative to the prostate, and they are different from one session to another and across imaging modalities and procedures."
In an effort to produce more accurate biopsies, Stoianovici, with urologist Misop Han, M.D., and postdoctoral fellow Doyoung Chang, Ph.D., has developed a Prostate Coordinate System (PCS), a frame of reference that could be assigned to the prostate of each patient, "with little variability among physicians, over time, and independent of the imaging used." Such a system could be a breakthrough in prostate navigation; imagine the difference to an ocean voyager of sailing to a particular latitude and longitude point instead of using geographic landmarks to find the way.
In a recent study, three urologists and three engineers were trained to use the PCS software and asked to assign the coordinates five times for three patients. The average time it took to assign the coordinate points was just over five minutes, and the results showed that "the PCS can be consistently assigned to the prostate in 3D transrectal ultrasound imaging," says Stoianovici. Further studies are necessary to confirm that the PCS can be consistently assigned using other forms of imaging, such as MRI. This work was supported by the Patrick C. Walsh Prostate Cancer Research Fund.