If you enjoyed this podcast, make sure to subscribe for more weekly education content from ASCO University. We truly value your feedback and suggestions, so please take a minute to leave a review. If you are an oncology professional and interested in contributing to the ASCO University Weekly Podcast, email ascou@asco.org for more information. TRANSCRIPT The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions. Guests on this podcast express their own opinions, experience, and conclusions. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement. Hello and welcome to the ASCO Guidelines Podcast series. My name is Shannon McKernin and today I'm interviewing Dr. Scott Morgan from the Ottawa Hospital and University of Ottawa, lead author on "Hypofractionated Radiation Therapy for Localized Prostate Cancer: an ASTRO, ASCO, and AUA Evidence-Based Guideline.” Thank you so much for being here today, Dr. Morgan. It's my pleasure, Shannon. I'm happy to take part in the podcast and hopefully share the highlights of the guideline with your listeners. So first, can you give us a general overview of what this guideline covers? Yeah. So the guideline covers really hypofractionated external beam radiation therapy, which is a treatment for localized prostate cancer, and for the non-radiation oncology folks in your audience, I think it's important to begin by placing the guideline sort of in its context and going over some of the terminology that we use as radiation oncologists. So external beam radiotherapy, it's a standard treatment-- standard local treatment option for men with localized prostate cancer. It gives outcomes which are really equivalent to those of radical prostatectomy or brachytherapy, which are the other two standard local treatment options. And traditionally, it's given in small daily fractions over several weeks and the usual daily fraction size is 1.8 to 2 Gray per day. And this is called conventional fractionation. And that really translates into a course of about seven and a half to nine weeks of treatment. And so that total dose which is delivered in those daily treatments, five days a week, is about 76 to 80 Gray. And that's what we call conventional or standard fractionation. And there's a theoretical framework in radiation medicine and there's some evidence to accompany that that suggests that prostate cancer is quite sensitive to radiation fraction size. And just to give a brief primer, for any tissue, cancerous or non-cancerous, there's a sensitivity to fraction size and it's characterized by something called the alpha-beta ratio. And for prostate cancer, that's felt to be low compared to most other cancers, the alpha-beta ratio, and indeed, it's thought to be lower than the adjacent dose-limiting normal structure, which is the rectum. And so an implication of that is that hypofractionation, and by that we mean daily fraction size of more than 2 Gray, might improve the therapeutic ratio of radiation therapy in localized prostate cancer. Now the guideline-- and I think it's important to emphasize this-- it draws a distinction between what we call moderate hypofractionation and ultra-hypofractionation. Clearly, fraction size is a continuous variable, so any subdivision that we might make is necessarily a bit arbitrary, but it turns out that at least in clinical practice, there's been really two distinct approaches to hypofractionation that have arisen. And one of these is moderate hypofractionation and that's an approach where the fraction size is modestly higher than 2 Gray per fraction, and in the guideline, it's been defined as a fraction size between 2.4 and 3.4 Gray, whereas ultra-hypofractionation, this is defined in the guideline as a fraction size greater than 5 Gray. And it's also been referred to in the litera