Would you have NODAL RT in 5 fractions?

[SongofFred]

Prostate SBRT in 5 fractions has now been adopted as standard of care for all risk levels of PCa. But doctors are now turning their eyes to nodal radiation (Whole Pelvis RT - WPRT) in 5 fractions as well.

I am having HDR Brachy boost therapy with follow up node radiation starting next week at UCLA. My doctor is offering the nodal radiation to be done in five fractions, as opposed to the standard 25. That would be 5Gy x 5= 25GY, over two weeks.

After researching as much as I could online, I spoke with both top Rad. Onc’s at UCLA. They both do it all the time. One thinks it’s equally curative, and the other thinks it’s more curative than 25 fractions. They think the toxicities are the same as 25, just earlier onset.

There have been a small number of trials I could find online. There does seem to be possibly worse erectile function in some of them, but it’s really hard to deduce because much of the time I’m only allowed to see an abstract which gives very limited data.

As to erectile function, one of the UCLA Drs said it’s hard to state long term ED because many of the men receiving nodal radiation are also going to be on ADT for a long time so post-ADT erectile function can’t be measured accurately.

I asked them what data they used to go ahead and they said they use shared info among other Doc’s at leading institutions, and indeed, many leading institutions are using it regularly including MSK, Sunnybrook, MD Anderson, UT Southwestern, and U. Toronto. This is data I’m not privy to, of course.

So is there a curative benefit and not just a time saving benefit? Could it be more ablative? My understanding is that each dose needs to be at least 8 or 9 Gy to become ablative. Don’t quote me on that, just read that in one paper online, but one of the UCLA Dr’s seemed to confirm that ablation only occurs with high dose SBRT or HDR Brachy to prostate, not the mere 5Gyx5 IMRT to pelvis.

But I’ve also read that PCa cells do respond better to higher doses in fewer fractions even though they’re not ablative (again, just my current understanding).

So here are the pros and cons I can think of so far:

Cons:

- It’s not a standard of care.

- Limited data/trials. (at least from the perspective of the patient)

- I’m not sure if toxicities are equivalent (but that’s only my lack of understanding).

Pros:

- Many high end institutions (listed above) have already adopted it.

- Possibly more curative

- 5 fractions are already being done on many other types of cancer such as rectal.

- Toxicities apparently are the same. (as per UCLA doc’s)

- Five+ years of data (though I’m not privy to it)

At some point I realized I personally don’t have the information I need to decide. I want to be my own advocate, but I can’t be my own doctor. I don’t want to talk myself out of a possibly better therapy just because I couldn’t figure it out myself. At some point one has to trust the expertise the doc’s have gained from a decade of med school vs. my few months of googling.

I asked them if I wasn’t comfortable with five what they would recommend and they both said 15 or 25. Well there’s not that much data on 15 so I guess 25 it is. But then, what if 5 is better. And I’m back to square one.

Any idea how you’d approach this? For some, it not being a standard of care is enough to nope right out. But at what point do you decide to give yourself over to an expertise that exceeds your understanding. Especially if there are many experts in agreement?

Any thoughts or experience is welcome.

Thank you.

(also, there are at least two current trials, HOPE and PRIME, built around the 5Gy x 5 WPRT protocol. If anyone has early insight, that would be quite helpful).

[Tall_Allen]

Follow Amar Kishan's advice. He has a linac (Viewray) that may minimize toxicity.

[Tall_Allen in reply to Tall_Allen]

BTW- they've been treating the pelvic LN area (25 Gy x 5 fx) in a clinical trial at UCLA since 2014.

[Tall_Allen in reply to Tall_Allen]

You may also be interested in these clinical trials at Cedars-Sinai (Zach Zumsteg is lead investigator):

clinicaltrials.gov/study/NC...

clinicaltrials.gov/study/NC...

[SongofFred in reply to Tall_Allen]

Interesting. Do you know the name of the UCLA trial? Neither Dr. mentioned it.

That first Cedars-Sinai trial closely resembles the GUIDANCE trial which is using Darolutamide instead and for a shorter duration. I happen to be following that protocol already.

[SongofFred in reply to SongofFred]

On further thought, this UCLA 5fx x 25Gy trial since 2014 is very important information. It means they’re actively following patients months and years after this protocol and know first-hand the results instead of going by reports of others. If they still have confidence after that, that changes things very much in my mind. Thank you!

(btw, is my understanding right about a higher dose per faction being more curative, even if each dose isn’t high enough to be ablative?)

[GP24]

I had my affected lymph nodes radiated with SBRT. No side effects and the affected lymph nodes were destroyed successfully. You need to combine it with ADT or new lymph nodes will occur soon.

[SongofFred in reply to GP24]

I imagine you got an ablative dose. Too much when doing the whole pelvic region. Yes, definitely on ADT.

[GP24 in reply to SongofFred]

With SBRT you would get a PSMA PET/CT first to locate the affected lymph nodes. Then you will spot radiate just these lymph nodes or add the ones close by to be on the safe side. Therefore you can apply a much higher dose than would be possible with IMRT.

The 5 times 5 Gy will result in 108 Gy BED total when using an α/β ratio of 1.5 for prostate cancer. radiobiology.org/bed1a.asp You will need over 100 Gy BED to destroy the lymph node mets.