SBRT for High Risk PC: Not quite as... - Prostate Cancer N...

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SBRT for High Risk PC

Tall_Allen profile image

Not quite as effective as Brachy Boost Therapy, but less toxic and more convenient.

prostatecancer.news/2021/01...

Edit 1/26/21 - I heard a rumor that Canada may be starting a randomized clinical trial this year called ASCENDE-SBRT. ASCENDE-RT was the trial that proved that brachy boost therapy was vastly superior to EBRT-only in high and intermediate risk men, although urinary toxicity was also higher:

prostatecancer.news/2017/03...

I think the new trial would randomize men to either:

(A) Brachy boost therapy: ADT+46 Gy/28 fractions of whole-pelvic IMRT + 115 Gy of I125 seeds in the prostate, or

(B) SBRT only: ADT+ 25 Gy/5 fractions of whole pelvic SBRT +additional 15 Gy/5 fractions to the prostate

Of course, it will be many years before we have any results.

32 Replies

As I said, IMRT is still a better therapy than SBRT for high risk patients. Despite the NCCN guideline that SBRT is a "reasonable" SOC. There is still a lot to be said for English sangfroid!

Tall_Allen profile image
Tall_Allen in reply to dexy1234

I'm not sure how you came to that unwarranted conclusion.

dexy1234 profile image
dexy1234 in reply to Tall_Allen

Stats, dear boy, stats....

Tall_Allen profile image
Tall_Allen in reply to dexy1234

I think I understand what you're misinterpreting. It helps me to get feedback that someone can read that article and draw the completely opposite conclusion. I can see that I made the erroneous assumption that the reader will understand that brachy boost therapy is the established SOC, having proven itself superior in ASCENDE-RT and several other randomized clinical trials.

In the ASCENDE-RT RCT (which randomized intermediate and high-risk patients to LDR brachy boost therapy (BBT) or EBRT only), bRFS was similar at 5 years but the "stats" deteriorated much more rapidly for EBRT:

5 year bRFS: EBRT=84% vs BBT=89%

9 year bRFS: EBRT=62% vs BBT=83%

(The stats are all proportionately lower for high-risk patients only, of course - Fig. 2c)

In statistical language, we say that the Kaplan-Meier curves began separating at around 5 years in favor of BBT.

I included stats on EBRT-only knowing its effectiveness wears off much more rapidly than higher dose therapies. The hope is that other higher BED therapies (like SBRT) have more of a sustained effect while having lower toxicity. IMRT is only a good idea for high -risk if one's life expectancy is less than 10 years.

It is also possible that you ignored my warning that the stats are only loosely comparable. They come from different trials with different men in each group. But even within each trial, there is variance. In the ASCENDE-RT RCT, for example, the 95% confidence interval is ± 6%. That is why the EBRT and the BBT outcomes are the same at 5 years (but vastly different later). The 95% confidence interval for the SBRT trials is much wider because it is the average of 8 different trials, each with slightly dissimilar patient characteristics and treatment parameters.

Sorry for the confusion. I will consider rewrites, so that others won't misunderstand the way you did.

Interesting comparison of the different radiation therapies. Even though SBRT lacks long term follow up it anyway could be the preferred RT. I don't understand why you included the riskcalc for surgery+SRT in the table. In a hypothetical randomized trial, not all men i the surgery group would need SRT so the bRFS for the full surgery group would be different (better) so another bRFS should be used to compare surgery, or do I misread the purpose of table?

Tall_Allen profile image
Tall_Allen in reply to Gemlin_

Most high-risk men are told by a urologist that RP + adjuvant RT is a good option. This is what D'Amico proposed. He argued that simply comparing surgery to brachy boost therapy (BBT) (the Gold Standard) is unfair. After all, he argued, BBT includes external beam radiation, hormone therapy, in addition to the intense prostate therapy. If surgery also included external beam radiation and hormone therapy, wouldn't the results be the same? He called this strategy "Max RP," and did a retrospective study, comparing it to BBT, which he called "MaxRT." You can read about it here:

prostatecancer.news/2018/11...

If one looks at Kishan's retrospective data limited to those who had MaxRP, 5-year prostate cancer-specific survival was twice as high when BBT was used. It seems that the heavier dose of radiation may be more curative, possibly because it doesn't leave cancer cells behind, as surgery might.

In Kishan's full data set, comparing 10-year prostate cancer-specific survival of BBT to surgery, PCSM was nonetheless twice as poor for RP as for BBT. In the full data set, 43% of the RP patients had adjuvant or salvage radiation. The RP patients were also younger and had more favorable disease characteristics than the BBT patients.

prostatecancer.news/2018/03...

So for the purposes of my table, I wanted to show biochemical recurrence rates at 5 years after "MaxRP." That nomogram is the largest of its kind and incorporates the experience of 2,460 patients treated with salvage radiation at 10 major institutions. 244 had a Gleason score of 8, and 390 received adjuvant ADT. It is the largest data source of "MaxRP" that I could find. I limited the high-risk characteristics to Gleason 8, put in zero PSA (adjuvant radiation), and no adverse pathology - I wanted to see the best possible results. At 5 years, the bRFS was pretty good - 78%. But by 10 years, it had slipped to 70%. (Compared to 83% at 9 years for BBT in the high-risk cohort treated with BBT in the ASCENDE-RT RCT)

Gemlin_ profile image
Gemlin_ in reply to Tall_Allen

Thanks for the explanation!

I am scheduled soon for EBRT(vmat)+HDR BBT at end of Feb. and have resisted starting ADT but have learned through research (much provided by you Tall _Allen) that my chances are much better with a year of ADT suggested by RO. I am 4+3 (stats in bio), and asked him about SBRT, which they do perform in Calgary but he has said that in my case that it would not be as effective. He would like me to start ADT asap and postpone treatment for another 2-3 months before beginning. ADT side effects don't sound too enticing, but feel as though it is my best chance. Unfortunately in Canada we dont get the choices available to you all south of the border. Am I still getting a good treatment with minimal long term effects, or should I push harder for SBRT. BTW, my first post here and sure appreciate your expert opinions and data...

Just to add to last post, HDR scheduled for end of Feb., with 15 sessions of EBRT to begin the middle of March. Hoping expertise level for procedures is high, no stats available for program. I am getting cold feet, wondering if I have made the right decision or if I should jump ship to the surgery bandwagon. This sure is a hard decision...

Tall_Allen profile image
Tall_Allen in reply to soabguy

I am a big fan of brachy boost therapy (BBT) for unfavorable risk PC. In fact, Canada is a leader in it - the ASCENDE-RT trial was Canadian. While BBT has been done since the mid-1980s, SBRT for high risk is the new kid on the block (although it has been used for unfavorable intermediate risk for quite a while). The opportunity for SBRT is to be as effective while having a lower risk of side effects. The Kishan study only reports results out to 4 years, which is when BBT really starts to show its stuff. Does SBRT have sustained oncological effectiveness (like BBT), or will results peter out over the next few years (like IMRT)? We can't answer that yet.

On the adjuvant ADT part of the treatment, a major randomized clinical trial found that 18 months is better than 6 months:

prostatecancer.news/2020/04...

Perhaps 12 months may be enough for your GS 4+3, but there is no data. Maybe, if you can get a Decipher test run on your prostate biopsy tissue, that can provide some assurance.

soabguy profile image
soabguy in reply to Tall_Allen

Good info, I have asked about geonomic testing such as Decipher but unfortunately it is not covered by Alberta Health Care at this time although my RO thought it wouldn't be long before it would be. Not sure what the cost is, perhaps I could pay on my own to have it done. I will inquire. What would be your opinion of the 15 sessions of VMAT after the HDR - is that going to help with the outcome, could SBRT replace it, or is it somewhat useless or overtreatment? Perhaps it is used to treat the area outside the prostate?

Tall_Allen profile image
Tall_Allen in reply to soabguy

I think Decipher costs about $4000.

Yes, the external beam part of the therapy treats an area outside of the prostate.

It would also be a good idea to check for metastases with a PSMA PET. There is a clinical trial at Royal University Hospitalin Saskatoon, Saskatchewan, if you can get into that one:

clinicaltrials.gov/ct2/show...

soabguy profile image
soabguy in reply to Tall_Allen

I would assume the possibility of metastases would be due to my GS 4+3, and that the CT whole body scan and 3TMRI are not as accurate as PSMA PET?

Tall_Allen profile image
Tall_Allen in reply to soabguy

Right. Pattern 4 can metastasize. It's not likely at your PSA, but the new PSMA PET scans are very sensitive. They can pick up cancer in lymph nodes even when the LNs are not enlarged (which is how CT scans find them). I hope that eventually it will be standard practice to give a PSMA PET scan to all unfavorable risk men.

Thank you Allen!!!

I asked my MO at Johns Hopkins about brachy boost several months ago after reading several comments where you said it was superior to IMRT (what I received in early 2020). He said it was not.

I’m not claiming it, but that is what he told me.

Tall_Allen profile image
Tall_Allen in reply to London441

Johns Hopkins has a surprisingly poor radiation oncology department. They are great at surgery and medical oncology, but it is the last place I'd go for radiation. In our era of highly specialized medicine, urologists and MO usually know diddlysquat about radiation oncology ( but that doesn't stop them from having an opinion.) Try Sean Collins at Georgetown instead.

London441 profile image
London441 in reply to Tall_Allen

I didn’t get my radiation there. However yes the MO there did express that opinion. Perhaps my best treatment options would have been split between different institutions. I never considered it. I picked a hospital known as a center of excellence that’s close to where I live.

I suppose I could have just consulted you when this all began, had I been gifted enough to know of you. You certainly have a depth of knowledge and some strong opinions.

Tall_Allen profile image
Tall_Allen in reply to London441

It's never a good idea to focus on regrets about what you should have done. It's always better to focus on the present moment. That's true that even many of the top institutions lack depth in some area or another. It's always a good idea to get references for specific doctors.

London441 profile image
London441 in reply to Tall_Allen

I don’t have any regrets, and won’t regardless of what happens.

If I end up having to go down the dark road (chronic disease phase) of further non-curative treatment options, like a gunslinger with a unknown number of bullets remaining-having no idea how long any one of them or a combination will keep the bandits at bay, until the bitter end, then I’ll do it one step at a time, making the most of what remains the whole way..

I am living and have lived a rich life. Present moment living I’m good at.

This crazy, insatiable super intelligent collection of diseases known as Pca....I had no idea what I was up against. And apparently no consensus among even the best experts on how to treat it.

Thank you for not reacting to my personal attack on you, for which I apologize.

treedown profile image
treedown in reply to London441

I wish I had been on this forum from day 1 but alas I was not. But it has done wonders for feeling I have a handle on what may come.

in reply to treedown

I'm with you and I already know what's coming next month....the bill for this month.

I added a rumor about a new Canadian RCT (above)

Tall.... Have you ever heard of SBRT involving an MRI before EACH and every one of the 5 individual treatments? I man on another site i belong to says that was how his SBRT was administered . Sounds like his docs were maximizing income, or is this a common method of SBRT I just havent heard of? Thanks.

Tall_Allen profile image
Tall_Allen in reply to kayak212

I have not heard about using an MRI only once at the beginning of each treatment. Viewray and Elekta now make linacs that use MR imaging continuously throughout each treatment (instead of fiducials).

The man who told me he got an MRI before each treatment said he was treated at MSKCC. Maybe what you DESCRIBE is what he was referring to because he said the purpose after each treatment was to deal with the possible movement of the PROSTATE between sessions.

treedown profile image
treedown in reply to kayak212

I got a low level CT scan before each of my treatments.

Yes, I'm aware that MSKCC has one of those fancy new linacs.

Tall..Well I am starting my SBRT treatments tomorrow at Emory. Already worrying about the side effects,especially FATIGUE. My PCP recently ran a blood test at my request because I have continued to feel tired even on my non workout days. He said the results showed I have what he called CHRONIC Disease Anemia which isn't the kind you cure with Iron pills etc but is instead due to my other CHRONIC health problems. I advised my RO of the findings but it won't stop my SBRT from proceeding. Hoping for the best. Can't thank you enough for all of your help and candid advice over the past several years. Not happy to come off of As and start treatment at 81,but my family and wife are so on we go!

Tall_Allen profile image
Tall_Allen in reply to kayak212

Fatigue is almost unknown as a side effect of SBRT. It increases with # of treatments.

That is a relief to hear. Those damned books they give you to read about radiation therapy , PCa etc before you start are alarming.

They cover their asses. It's like reading the detailed prescription info for any drug. Here's what you can reasonably expect:

prostatecancer.news/2018/10...

I think you'll find the treatments themselves are a big nothing. Be sure to exercise and take ED meds.

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