Hypofractionated Radiation Therapy for Localized Prostate Cancer Guideline

An interview with Dr. Scott Morgan from the Ottawa Hospital and University of Ottawa on "Hypofractionated Radiation Therapy for Localized Prostate Cancer: an ASTRO, ASCO, and AUA Evidence-Based Guideline." This guideline provides recommendations on hypofractionated external beam radiation therapy for localized prostate cancer.

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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 literature as extreme hypofractionation or Stereotactic Body Radiation Therapy, SBRT, or SABR, Stereotactic Ablative Radiation Therapy.

But in any case, we are talking here about, with ultra-hypofractionation, with radical courses of treatment that are often delivered over as few as five fractions, often on an alternate day approach over two or two and a half weeks. And so the guideline really was largely motivated by the publication of a number of randomized trials, including four large-scale trials in the past two years that have compared conventionally fractioned radiation therapy and moderately hypofractionated radiation therapy. So that is really what stimulated the guideline, which was the evidence concerning moderately hypofractionated radiation therapy.

But at the same time, there has been an increasing use in routine clinical practice that's been observed of ultra-hypofractionated radiotherapy, so the decision was made to make recommendations on it as well. So ASTRO, American Society for Radiation Oncology, in collaboration with ASCO and the AUA, convened a panel of radiation oncologists, medical physicists, urologists, radiation oncology resident, patient representative, and a systematic review of the literature was conducted and their recommendations have been made on the basis of this systematic review. So the aim was to provide recommendations on use of both moderate hypofractionation and ultra-hypofractionation, in particular with reference to oncologic outcomes, toxicity, and quality of life. So we didn't directly consider health economic endpoints, though clearly the very nature of hypofractionation is such that there are potential advantages in terms of cost and convenience for patients.

And what are the key recommendations of this guideline?

We separated the key recommendations into three main groups and the first set of recommendations pertains to moderate hypofractionation, and these are generally based on the highest-quality evidence. So they could be viewed as the strongest recommendations in the guideline. And the second set of recommendations concern ultra-hypofractionation. They're somewhat less strong given they're based on somewhat weaker evidence. And then the third set of recommendations relate to some of the technical aspects of the planning and delivery of hypofractionated radiation therapy.

So, dealing with the moderate hypofractionation recommendations first, arguably the most important recommendation of the guideline is that the panel has recommended that in patients with localized prostate cancer who are candidates for external beam radiation therapy, moderate hypofractionation should be offered. And this is graded as a strong recommendation. It's based on high-quality evidence and it applies to patients across all risk groups.

So it applies to patients with low-risk prostate cancer who require active treatment or who have declined active surveillance and it also applies to patients with intermediate-risk or high-risk localized prostate cancer. And why really does it apply to all these groups? It's essentially because these groups are well-represented in the trials of moderate hypofractionation. And the trials have shown that moderate hypofractionation really gives similar outcomes in terms of efficacy to conventional fractionation.

Now one caveat I guess that I should say is that the trials generally only looked at radiation therapy to the prostate rather than radiation therapy to the prostate as well as the pelvic lymph nodes. So the panel's recommendations regarding moderate hypofractionation don't apply to the scenario where the clinician has decided to include the pelvic lymph nodes in the radiation therapy volume. The panel also made recommendations with respect to toxicity and quality of life, and specifically, they did recommend that men should be counseled about a small increased risk of acute gastrointestinal toxicity, typically rectal toxicity, with moderately hypofractionated radiation therapy. And they should also be counseled that moderately hypofractionated radiation therapy has a similar risk of late GI toxicity and also has a similar risk of both acute and late GU toxicity compared to conventional fractionation. The only difference was seen in acute GI toxicity.

And I think it's probably worth dwelling on this a little bit more. Probably the most granular data on acute GI toxicity comes from the CHHiP trial. This was a trial from the UK. It was far and away the largest randomized trial of moderate hypofractionation versus conventional fractionation.

And they followed the amplitude of GI toxicity very carefully over the short and long term and what they did found was that in the early weeks, there was greater peak acute GI toxicity with moderate hypofractionation, but this difference had really disappeared by about 18 weeks after the start of radiotherapy. So within a few months, there was no difference, and afterwards, there was no consistent difference in long-term GU or GI toxicity across these trials. Now I guess I should mention that, at the current time, that the median follow-up of most of these trials is between five and six years, so arguably, the last word hasn't been written.

The panel also offered conditional recommendations on particular moderate hypofractionation regimens. There were multiple different regimens that were evaluated but most were not compared head-to-head. And the panel preferred two particular regimens-- 60 Gray and 20 fractions over four weeks or 70 Gray and 28 fractions over five and a half weeks, as these were the two regimens that were evaluated in the largest populations. And of these two, likely the strongest evidence supports 60 Gray and 20 fractions, given it was used in two different trials and it was used across all risk groups and with or without concomitant hormonal therapy. So those were the recommendations regarding moderate hypofractionation.

So moving to ultra-hypofractionation, again, this is talking about fraction size of at least 5 Gray, typically a course of as few as five fractions over perhaps two or two and a half weeks. I think it's important to say that, at the time we were preparing this guideline, there were no published efficacy or toxicity data from randomized trials comparing ultra-hypofractionation and conventional fractionation. So the strengths of the recommendations made by the panel is correspondingly lower than was the case for moderate hypofractionation.

But having said that, there are several prospective non-randomized studies that have been published and have documented safe delivery of ultra-hypofractionation for appropriately-selected patients and pretty good biochemical control and low toxicities have been observed in these studies. But again, relatively few have follow-up beyond five years.

So what the panel recommended was that in men with low-risk prostate cancer-- and the bulk of the data to date for ultra-hypofractionation has been in this group-- panel conditionally recommended that in those who decline active surveillance and choose active treatment with radiation therapy, that ultra-hypofractionation may be offered as an alternative to conventional fractionation. Again, this is a conditional recommendation.

In men with intermediate-risk prostate cancer, the panel has conditionally recommended that ultra-hypofractionation may be offered as an alternative to conventional fractionation but it's strongly recommended in this group that these patients be treated as a part of a clinical trial-- and there are several clinical trials ongoing-- or as part of the multi-institutional registry. And then finally, in patients with high-risk localized prostate cancer, there was really insufficient comparative evidence for the panel to suggest offering this outside of a clinical trial or outside of a registry.

Regarding particular regimens, that the panel again made a conditional recommendation that a schedule of 35 Gray to 36.25 Gray and five fractions delivered to the planning target volume could be offered and that it recommended against consecutive daily treatments for this schedule. So I think it's again important to note that compared to moderate hypofractionation, the ultra-hypofractionation literature is really substantially less mature and it is evolving rapidly. And therefore, a short-term update of this guideline to address new data pertaining specifically to ultra-hypofractionation is likely going to be necessary.

And then I mentioned there was a third set of recommendations and these pertain to the technical aspects of planning and delivering radiation therapy. And these probably are not of core interest to your audience, but briefly, the guideline recommends that in the planning of hypofractionated radiotherapy, that normal tissue constraints and target volumes derive from published reference standards the use and that image guidance and intensity modulation at one form or another are recommended in delivering hypofractionated radiotherapy.

Great. Thank you for the overview of those guideline recommendations. So why is this guideline so important and how will it change practice?

Yeah. I guess the first point to make is that the guideline potentially can inform the care of a very large number of patients. Across North America, about 200,000 patients a year are diagnosed with prostate cancer and its far and away that the most prevalent non-dermatologic cancer in men and it's the third-leading cause of cancer death in men, at least in North America. So the vast majority of those 200,000 men are diagnosed with localized disease at the time of presentation and therefore they're potentially treatable with radiation therapy and therefore the guideline is relevant to these patients.

Prior to the publication of the trials that motivated this guideline, the overwhelming majority of these men who chose external beam radiotherapy as their primary treatment have been treated with conventionally fractionated therapy. In other words, seven and a half to nine weeks of treatment. And already, since the publication of these trials-- the trials of moderate hypofractionation-- we're talking really about moderate hypofractionation because I think that is where the guideline will have its impact, at least in the short term. In the jurisdiction where I practice in Canada, practice has already substantially changed in light of these trials, and I think a large majority of patients with localized prostate cancer choosing external beam radiation therapy are now typically being treated with a moderately hypofractionated approach, typically a four-week schedule. So it will be interesting to see if a similar change is occurring or will occur over time in the United States, particularly informed or potentially informed in part by this guideline.

And then finally, with respect to ultra-hypofractionation, I think again I have to note that this is a very dynamic space in terms of evidence and there are a number of large-scale trials looking at ultra-hypofractionation and comparing it to either conventional fractionation or moderate hypofractionation that are in progress or near to reporting. And so again, an update of the guideline in the short-term as data emerges from these studies will likely be important and it may ultimately influence practice as well on a large scale.

And finally, how will these guideline recommendations affect patients?

So I think in the short term, that the recommendation that has the potential to impact patients in the greatest way is the recommendation regarding moderate hypofractionation. And the guideline really recommends that this is a management approach that substantially reduces the treatment burden without compromising treatment efficacy and without increasing the risk of long-term side effects. So in my view, the move to moderately hypofractionated radiation therapy is a win for patients with localized prostate cancer who choose radiation therapy as their primary treatment modality.

And so moderate hypofractionation really represents about a halving of the overall treatment time in some patients. And those who live, for example, in rural or remote areas and who need to travel considerable distance to have their treatment, a halving of treatment time is significant. But I think even more generally, halving of treatment time is significant for patients regardless of where they live. And clearly there are also benefits potentially in terms of cost and also benefits in terms of for the health care system but those really weren't specifically studied in the guideline.

Great. Thank you so much for your time today, Dr. Morgan, and thank you for your work on this important guideline.

My pleasure, Shannon, and thank you for having me.

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