I have found the PSA doubling time to be an important parameter to consider when treating postoperative prostate cancer patients with a rising PSA. Many of these patients have a very slowly rising PSA and probably will never be affected by their recurrent disease. I found myself having to go online over and over to get to a PSA doubling time calculator so that I could plug in the latest dates and PSAs for my patients to do the calculation and longed for an easier and quicker solution. The PSA doubling time assumes exponential cell growth and so the raw PSA value is typically converted to a log value before doing the calculation. I started out trying to find a linear regression program written in objective c and after failing to find anything, wrote one myself. I used the linear regression program to calculate the regression of the log(PSA) over time. The doubling time is the log(2)/slope of the calculated regression line. I have checked the regression calculator online comparing the values it gets versus an online version and found the calculations to be accurate. Please use good clinical judgement before depending on the values this program calculates and I would advise checking it's results against an online version initially. If you discover any issues with this program, please feel free to contact me Phillip P. Porch, MD