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Medical Forum / Diseases and Disorders / Prostate Cancer / December 2005Doubling time
Friends, Is there some kind of formula that is used to determine one's PSA doubling time? Warren, peace Warren it got the following information from Leonard Evens, who's a frequent poster here. Mark If the doubling constant stays fixed, then the formula would be as follows. Suppose you have PSA values P1 and P2 taken at times t1 and t2. The doubling time would be T = (t2 - t1) log(2)/log(P2/P1) Suppose for example that you had two readings of 2.5 and 3.5 four months apart. Then t2 - t1 would be 4 months and the formula would give T = 4 log(2)/log(3.5/2.5) ~ 8.24 months In practice however, it is a bit more complicated. There are always some measurement errors. If you have more than two measurements, you would have to use a least squares procedure to determine the best line fit to log(P) as a function of time t and proceed from there. You could also use the above formula for different pairs of PSA values at different times and then take the average of the values you obtained. That would probably be close enough. In addition, the PSA doubling time could be changing with time, and that would complicated things even more. > Friends, > [quoted text clipped - 3 lines] > Warren, > peace On Christmas Eve, Warren inquired: > Is there some kind of formula that is used to determine one's PSA > doubling time? Well, a kinda scary response has been posted by MAJ. I don't think it's all that complicated, and requires little but basic arithmetic skill. Here's the definition of PSADT from the website of the Prostate Cancer Research Institute: "PSA doubling time (PSADT): the calculation of the time it takes for the PSA value to double based on at least three values separated by at least three months each; before diagnosis, a PSADT of less than 10 years may be an indication of the presence of PC." And from "What Every Doctor Who Treats Male Patients Should Know," a May 2005 paper by Strum and Pogliano that all of us should copy and give to our primary care physicians. "PSA velocity (PSAV) and PSA doubling time (PSADT) are important markers that can indicate the existence of prostate cancer. Blood sampling for PSA determinations, done at least three months apart, and by the same laboratory using the same testing procedure, are necessary to establish PSAV and PSADT. The validity of such determinations is increased if such testing involves at least three determinations over an 18-month span of time. However, a progressive and serial increase in PSA values should raise concern that prostate cancer is present and that a greater degree of vigilance is mandatory. • A PSAV that exceeds 0.75 ng/ml/yr is associated with a higher probability of PC.8 • A PSADT of less than 12 years is associated with a higher probability of PC." Here is the link to the article: http://www.prostate-cancer.org/education/preclin/StrumPogliano_EveryDocShouldKno w.html Regards, Steve J "The thing is to expect nothing in particular, but be aware of the lack of enforceable guarantees or enforceable contracts with nature/god/entropy as to the condition or durability of our bodies." -- Brian Brunner, PCa survivor, December 12, 2005 on The Prostate Problems Mailing List Thank you, Brian, for your insight. > On Christmas Eve, Warren inquired: > [quoted text clipped - 5 lines] > I don't think it's all that complicated, and requires little but basic > arithmetic skill. I'm afraid it is exactly as complicated---or simple, depending on your perspective---as MAJ described. Anyone with a scientific calculator with a log key can use the formula he gave for two measurements. For three or more measurements it is more complicated. As he says, if the PSA is following the model, then you could use a least squares line for log P, but most lay people wouldn't know what that means and wouldn't have the tools to do it. An alternative would be to use the formula with different pairs of values and estimate the doubling time for each such pair. Then you could compare the values you got. If they showed very different values, then that would indicate the model probably didn't apply. If they showed similar but different values, that could give you some estimate of the approximate doubling time. It is important to remember in all this, as my urologist likes to say, it isn't rocket science. Gross differences in doubling times can mean something, but relatively small differences are probably meaningless. Your doctor should have software tools available to indicate a doubling time if he is going to use it in diagnosis. But it would only be one tool and more likely than not, just a glance at the figures would give him enough information, together with the other data, to help draw a conclusion. Here's the definition of PSADT from the website of the > Prostate Cancer Research Institute: > > "PSA doubling time (PSADT): the calculation of the time it takes for the > PSA value to double based on at least three values separated by at least > three months each; before diagnosis, a PSADT of less than 10 years may > be an indication of the presence of PC." This is a definition, but it doesn't tell you how to find the doubling time from values if the ratio of the values during the time interval is not a doubling. > And from "What Every Doctor Who Treats Male Patients Should Know," a May > 2005 paper by Strum and Pogliano that all of us should copy and give to [quoted text clipped - 29 lines] > Problems Mailing List > Thank you, Brian, for your insight. Geez, guys ... just Google up a PSA doubling time calculator, plug in your PSA values and dates, and hit ENTER. Viola! If you can read this, you can do it. ;-) I.P. Yea! That's exactly what I need I.P. :) Thanks to all for the replies. From a man who doesn't know his arithmetic. Warren, peace > Geez, guys ... just Google up a PSA doubling time > calculator, plug in your PSA values and dates, and hit > ENTER. Viola! If you can read this, you can do it. ;-) > > I.P. > Geez, guys ... just Google up a PSA doubling time calculator, plug in your > PSA values and dates, and hit ENTER. Viola! If you can read this, you can > do it. ;-) > > I.P. Thanks for the common English answer... (I am NOT a math geek; when I see logs, I flush!) >>Geez, guys ... just Google up a PSA doubling time calculator, plug in your >>PSA values and dates, and hit ENTER. Viola! If you can read this, you can [quoted text clipped - 5 lines] > > (I am NOT a math geek; when I see logs, I flush!) I hope you found a doubling time calculator. There is a decent one at the Sloan-Kettering web site: www.mskcc.org/mskcc/html/10088.cfm As I noted previously, it is not wise for a layman to try to make too much of information of this kind without consulting a medical expert. That would be true even for the "math geeks". In using a calculator, make sure you include only values during the period in which your PSA was increasing, and don't try to read too much into the answer. By the way, "geek" is not a term of admiration. I believe it refers to a circus side show performer who does wild things like biting the heads off chickens. It has in recent years come just to mean a scientifically or technically inclined person, but I think it still has some negative connotations, particularly among us old-timers. There seems to be an implicit suggestion that there is something odd about people who do understand logarithms. Perhaps you should be thankful that there are some "geeks" out there who can invent such ideas for your benefit. ;-) > By the way, "geek" is not a term of admiration. ...then... > It has in recent years come just to mean a > scientifically or technically inclined person, ... if those aren't contradictions, you *might* be a luddite! > but I think it still has > some negative connotations, particularly among us old-timers. My Age: 13 with 37 years experience. I think you're thinking nerd, dork, or jerk. Geek is a positive term. I am a geek, not a math geek. Savvy? There are 10 kinds of people in this world: those who understand binary, and those who don't. Here is information about the Sloan-Kettering online calculator. It is possible that it applies to other PSA doubling-time calculators.: Who Can Use This Tool? \\\ For Those Who Have Not Been Treated The tool is designed to be used by patients who have had a biopsy of the prostate confirming the presence of cancer. The biopsy must have had a Gleason grade assigned to it. The patient must also have had a PSA blood test performed, either prior to or not within 10 days following the biopsy, and not after the start of hormonal therapy if hormones have been started. The patient must also have been assigned a clinical stage using either the 1992 or 1997 clinical staging systems. The tool can also be used by patients who are considering hormone refractory therapy. The tool cannot be used for patients whose prostate cancer is believed to have spread to other parts of the body, such as bones or lymph nodes. \\\ For Patients Who Have Been or Are Receiving Treatment The tool can be used by patients who have received prostatectomy to treat the prostate cancer within the past 6 months. This tool is not for patients who have received hormonal therapy or radiation therapy either prior to or following surgery. This tool is also not for the patient who had surgery longer than 6 months ago. > [Geek] has in recent years come just to mean a scientifically or > technically inclined person, but I think it still has some negative > connotations, particularly among us old-timers. There seems to be an > implicit suggestion that there is something odd about people who do > understand logarithms. Perhaps you should be thankful that there are some > "geeks" out there who can invent such ideas for your benefit. ;-) Sadly (from an American's perspective), we are a rapidly shrinking breed in this country. I.P. >> [Geek] has in recent years come just to mean a scientifically or >> technically inclined person, but I think it still has some negative [quoted text clipped - 7 lines] > > I.P. Well, I must say that I'm affectionately considered the extended family's computer geek -- from the D.C. area to San Fran, Oklahoma, Albuquerque, Arizona, Michigan and points between. Sorry to not fit the stereotype 'cuz I golf, travel, read, socialize, fish, hunt, etc. Used to hike but that's temporarily difficult but I see light at the end of the tunnel. Just finished my latest geekie thing. Fixed my visiting daughter's Dell laptop that refused to boot beyond the sign-in screen. Turned out to be a poor job of installing heat sink grease on the CPU. Burned up 6 hours but enjoyed the challenge. She was ready to spend $700 on a new one. Cheers! > Sorry to not fit the stereotype 'cuz I golf, travel, read, socialize, > fish, hunt, etc. Used to hike but that's temporarily difficult but I see > light at the end of the tunnel. To me, geeks are technophiles, even if they're also jocks. Many, maybe most, of my friend, and the vast majority of my coworkers, have always been geeks. But many, maybe most, have also been athletes, some very serious ones. The smartest engineer I ever knew was also a Navy fighter jock with two tours in Viet Nam. The biggest, strongest, best athlete I hang with now is also the smartest engineer I know these days. The only stereotype I would pin to a "geek" is an education in the physical sciences (e.g., physics, engineering, math); the rest of his/her makeup is highly variable. I see nothing derogatory about that term. Now NERDS, to me, are a subset of geeks, geeks who couldn't find their way around an oval track or off a basketball court, figure out which end of a hammer to use. And, hey, if they're happy, so what if they wear Star Trek Jockey shorts and don't date until they're 25. After all, wasn't Bill Gates the ultimate nerd before he grew up to become the ultimate geek? I.P. >> Sorry to not fit the stereotype 'cuz I golf, travel, read, socialize, >> fish, hunt, etc. Used to hike but that's temporarily difficult but I [quoted text clipped - 17 lines] > > I.P. NERDS: We used to joke that we kept our computer nerds in the back room; opened the door and threw them a piece of raw meat once a day. They were happy to work with their computers 24 hours a day but needed food and water to survive and little else : ) Don > Well, I must say that I'm affectionately considered the extended family's > computer geek -- from the D.C. area to San Fran, Oklahoma, Albuquerque, [quoted text clipped - 3 lines] > fish, hunt, etc. Used to hike but that's temporarily difficult but I see > light at the end of the tunnel. Personal computers burst upon this world during 1980 and they were such an immediate success that there were not enough geeks to take care of them all. People who golf, travel, read, socialize, fish, hunt, etc., filled the void. I bought a TRS-80 from Radio Shack when their Model 3 was just released. Later I upgraded to a 286 and then, by 1992, a 486. My company had not kept up, putting all its money in CTOS (1984 technology). After several reports (read lamentations) regarding my ability to do more at home than at work, during 1994, I was taken out of operations and told, "if you don't like it, fix it." So, forming our first IT group, I chose a mediocre operations supervisor to be my #2 man. I chose him because I knew there was nothing inside the box he couldn't figure out. I went to a seminar in networking. And between the two of us (and a lot of money), we designed and installed 17 local area networks in 4 years. ... and suddenly I was a geek! It's taken me several years to live it down.  SignaturePSA 16 10/17/2000 @ 46 Biopsy 11/01/2000 G7 (3+4), T2c RRP 12/15/2000 G7 (3+4), T3cN0M0 Neg margins PSA .1 .1 .1 .27 .37 .75 EBRT 05-07/2002 @ 47 PSA .34 .22 .15 .21 .32 Lupron 07/03 (1 mo) 8/03 (4 mo), 12/03, 4/04, 09/04, 01/05, 5/05, 10/05 PSA .07 .05 .06 .05 .08 Non Illegitimi Carborundum > I bought a TRS-80 from Radio Shack when their Model 3 was just released. > Later I upgraded to a 286 and then, by 1992, a 486. My company had not [quoted text clipped - 7 lines] > designed and installed 17 local area networks in 4 years. ... and suddenly > I was a geek! Very similar experience! Ordered one of the first TRS80s in December '79. All of 4K RAM and a cassette drive. By the early 70s, I had already established our first IT group in facilities management at a Big Ten University. It violated University policy so we had to keep a low profile. No IT titles for anybody; Engineers, Technical Analysts, Accountants but everybody was really an IT expert. Department was called "Cost and Procedures" since nobody would associate that with IT. The Ad Building knew what we were doing but we had cornered University IT into agreeing to let us run with it since there was no way they could deliver on our objectives. When I retired in 1999 we had a 250+ work station network; and University-wide CAD systems, telecommunications, broadband, centralized environmental control and more than I can list under our control. The good old days : ) Hail to the geeks! One can even download to one's PDA by going to the "Request Downloadable Software" link at http://www.mskcc.org/mskcc/html/5794.cfm. Then you can amaze your friends.... > >>Geez, guys ... just Google up a PSA doubling time calculator, plug in your > >>PSA values and dates, and hit ENTER. Viola! If you can read this, you can [quoted text clipped - 26 lines] > that there are some "geeks" out there who can invent such ideas for your > benefit. ;-) Warren, It is rather simple. Buy semi-log paper. To plot the curve you will need the PSA results (need at least 3 measurements to ensure that indeed your growth is exponential by producing a straight line) and the period of time elapsed between PSA results. Not rocket science. All I am proposing is to use a standard curve-fit methodto at least 3 (preferably more) consecutive PSA values to determine (a) that the growth is exponential, and hence represents cancer; and (b) as good a value as possible for the doubling time. Semi-log paper will have exponential grading on the vertical axis (in this case the PSA axis) and the horizontal axis has a linear grading (in this case time elapsed). The formulas given will provide a doubling time between two measurements (if those points happen to be on a true straight line when more measurements are obtained and plotted later. If not, your DT calculation could be potentially innacurate. The beauty of a plot is that you can visibly see your doubling time without complicated mathematical formulas or the need of log tables or calculators with log functions. If you have Excel in your puter you can plot your PSA there and obtain a semi-log printout. Frank > Warren, > It is rather simple. Buy semi-log paper. Thanks. I've plotted my three readings after Lupron and they form a flattening parabolic arc. Looks like a thrown baseball just about to start falling. >>Warren, >>It is rather simple. Buy semi-log paper. > > Thanks. I've plotted my three readings after Lupron and they form a > flattening parabolic arc. Looks like a thrown baseball just > about to start falling. If it looks like that, then it is not obeying the exponential growth rule. If so, then the concept of doubling time doesn't make sense. Alternately, you could say the doubling time is changing. If the PSA stays constant, the doubling time is infinite. If the PSA starts dropping, then you would be interested not in the doubling time, but in the time it takes to drop to half its value, which could be interpeted as a negative doubling time. For that reason I reiterate my previous advice. Don't try using any of the calculators. Rather ask your doctor to interpret the meaning of the figures. > Don't try using any of the calculators. Rathe > ask your doctor to interpret the meaning of the figures. My PCP didn't even recognize a waving red flag PSA. I'm certain he's never heard of doubling time. I.P. If you are on Lupron, depending on how androgen dependent is your tumor volume and how fast/slow these cancer cells are killed, your PSA will vary and not respond exponentially, hence your parabolic curve |
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