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Magic alpha number likely higher in prostate cancer tissue

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Int J Radiat Oncol Biol Phys. 2010 Jun 15. [Epub ahead of print]

Deriving Prostate Alpha-Beta Ratio Using Carefully Matched Groups, Long Follow-Up and the Phoenix Definition of Biochemical Failure.

Shaffer R, Pickles T, Lee R, Moiseenko V.

Department of Radiation Oncology, British Columbia Cancer Agency, Vancouver, Canada; Department of Clinical Oncology, Imperial College London National Health Service Trust, London, United Kingdom.


PURPOSE: Prior studies have derived low values of alpha-beta ratio (alpha/beta) for prostate cancer of approximately 1-2 Gy. These studies used poorly matched groups, differing definitions of biochemical failure, and insufficient follow-up. METHODS AND MATERIALS: National Comprehensive Cancer Network low- or low-intermediate risk prostate cancer patients, treated with external beam radiotherapy or permanent prostate brachytherapy, were matched for prostate-specific antigen, Gleason score, T-stage, percentage of positive cores, androgen deprivation therapy, and era, yielding 118 patient pairs. The Phoenix definition of biochemical failure was used. The best-fitting value for alpha/beta was found for up to 90-month follow-up using maximum likelihood analysis, and the 95% confidence interval using the profile likelihood method. Linear quadratic formalism was applied with the radiobiological parameters of relative biological effectiveness = 1.0, potential doubling time = 45 days, and repair half-time = 1 hour. Bootstrap analysis was performed to estimate uncertainties in outcomes, and hence in alpha/beta. Sensitivity analysis was performed by varying the values of the radiobiological parameters to extreme values.

RESULTS: The value of alpha/beta best fitting the outcomes data was >30 Gy, with lower 95% confidence limit of 5.2 Gy. This was confirmed on bootstrap analysis. Varying parameters to extreme values still yielded best-fit alpha/beta of >30 Gy, although the lower 95% confidence interval limit was reduced to 0.6 Gy.

CONCLUSIONS: Using carefully matched groups, long follow-up, the Phoenix definition of biochemical failure, and well-established statistical methods, the best estimate of alpha/beta for low and low-tier intermediate-risk prostate cancer is likely to be higher than that of normal tissues, although a low value cannot be excluded. Copyright © 2010 Elsevier Inc. All rights reserved.

{jm: if alpha/beta for prostate cancer is 30 Gy, my HDR-ERBT is equivalent to 68 Gy}

PMID: 20558012 Forum: Other prostate cancer topics including radiation Title: Magic alpha/beta number likely higher in prostate cancer tissue

This extract can be found on http://PubMed.com, and is in the public domain.

On PubMed.com there will be a link to the full paper (often $30, sometimes free).

Any highlighting (except the title) is not by the author, but by Jim Marshall.

Jim is not a doctor.

This page was found on the Advanced Prostate Cancer Community for Australian men at http://advancedprost...lia.ipbhost.com.

The link is hard to remember.

An easier way to find it is to go to JimJimJimJim.com and click on Prostate.

That's the word Jim four times, no spaces, followed by .com.

If you need other help - to perhaps find someone to talk to or a local support group:

Click on the Contact Jim button at http://JimJimJimJim.com.

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