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Re: Hypoxic Prostate/Muscle Po2 Ratio Predicts for Outcome in Patients With Localized Prostate Cancer: Long-Term Results. Aruna Turaka, et al. International Journal of Radiation Oncology * Biology * Physics. Volume 82, Issue 3, Pages e433-e439, 1 March 2012 Dear readers, As I have a long-standing interest in near real-time physiologic monitoring of prostate cancer radiotherapy response, I read this article with both interest and reservation. Partly it was because of my disappointing personal experience with Eppendorf Po2 measurement. First off, the name microelectrode is a misnomer in this age when micro usually means measurement in microns. I have several comments for the authors: 1. The measurements of the prostate Po2 were performed when the patients were under general anesthesia, would the authors think that may cause some or most of the hypoxia in the prostate? Did the muscles have a ‘steal’ increase in blood flow? 2. Furthermore, most of the brachytherapy dose will be delivered during the first two months after the brachytherapy, why did the authors think that measurements done under general anesthesia on one day was representative of the prostate oxygenation status? 3. I think that the tissue oxygen tension sampling using the Eppendorf needle is very limited. The associated bleeding itself may cause problems for the measurement. How did the authors localize where the samples were taken? 4. For these reasons, I have been advocating an non-invasive optical tomography to monitor prostate and prostate cancer treatment response (1, 2). This method will allow for repeated measurements without anesthesia of the entire prostate and prostate cancer with good visualization. What do the authors think about this idea?

Reference: 1. The need and prospect of individualized external beam radiotherapy dose escalation beyond 80 gy to treat prostate cancer: in regard to Eade et al. (Int J. Radiat. Oncol. Biol. Phys. 2007;68:682-689). Cheung MR. Int J Radiat Oncol Biol Phys. 2008 Feb 1;70(2):645. 2. Using a priori structural information from magnetic resonance imaging to investigate the feasibility of prostate diffuse optical tomography and spectroscopy: a simulation study. Li C, Liengsawangwong R, Choi H, Cheung R. Med Phys. 2007 Jan;34(1):266-74.