High Risk Prostate - GETUG 18 - Conventional fractionation - Improved OS

[RickyScott]

I am not sure you need fiducials with spaceoar?

---

Members don't see this ad.

 

[evilbooyaa]

What dose do you aim for the SIB?

100+ if in 44Fx to be equivalent EQD2 wise to 95Gy in 35 fractions. It's routinely not covered well due to respect urethra or rectum tolerances. If I can get 50% of the GTV getting that I'm happy.

Well the majority of rad oncs out there are still just treating the whole prostate to 79.4/44 or 70/28 without a focal boost. And we know that works well and is tolerated well. MSK data went to about what I'm doing now.
I don't have spacer available in majority of patients and most of these lesions are posterior. I delineate urethra (as best I can) and constrain a 2mm PRV (with much tighter constraints than yours). Haven't been comfortable doing more than my "gentle" regimen of pushing more dose into the tumor and putting hot spots in it.

Without fiducial markers, I'm not extremely confident in daily soft tissue matching off of cone beam especially with hip implants. I instruct therapists as best I can but it's still all over the place. I may start going to 2 Gy/fx (that's 90 Gy we are talking about a few mm from the rectum!). And we all know the variation in bladder and rectum from sim to daily treatments. What you plan to is not going to be what's delivered. The goal is to get as close as possible, but it's not an exact science in this anatomic region.

This is a medicolegal area I'm not extremely thrilled to wade too deeply into.

FLAME is data of bPFS benefit with isotoxicity. It's hard to argue against beyond just 'I'm uncomfortable with it'. FLAME showed that it worked well and was tolerated well. MSK took whole gland to 86.4, and yeah they said it was OK, but I'm always skeptical that everything at MSKCC does perfectly well with no toxicity on their single institution analyses.

If most lesions are posterior and abutting the rectum, then that's unfortunate and I agree, keep the treatment isotoxic. But I think FLAME showed most lesions were getting like 50% of GTV safely getting that dose. And even that does help.

2mm PRV for urethra very reasonable. What are your urethral constraints in the 44Fx space? You're saying you limit urethra to Rx dose and accept underdosing of central prostate?

FLAME boosting does not require a spacer. Yes, in patients with posterior lesions who get FLAME boost it may help to allow more of the GTV to get better coverage with the boost, but not necessary.

I appreciate the discussion and I don't mean to come off as critical. I'm just saying if you're doing contemporary margins on prostate cancer (5mm) or less, you are in a better position than you think to do FLAME.

You're absolutely right that what is planned is not what's delivered. I frequently export an IDL to the CBCT and instruct therapists to ensure that the rectum is not within that line. It's usually not the whole gland Rx dose but maybe 105% of that (so like 105% of 79.2Gy).

Hip implants can definitely be an issue especially with older CBCTs, especially if bilateral, and if a majority of your patients have b/l hip replacements, then sure, you have a different population than me and maybe FLAME is inappropriate for them. B/L hip implants in a patient with routine constipation issues and inability to empty his rectum despite development of a laxative schedule is not a great candidate for a FLAME boost.

I will say that I am aggressive about max rectal anterior/posterior dimensions at CT sim and for treatment. Ideal < 3cm, and I won't accept sim at > 4cm unless it's at least the second day we've tried the sim. Treatment a bit more flexible, but again, keeping some isodose line out of the rectum.

I am not aware of a medicolegal case in this realm. You have good defense by saying you were following the FLAME regimen, IMO, but I know I won't convince you otherwise of that.

Do you get a fresh MRI if the patient has been on neoadjuvant ADT? The issue I ran into recently was I got a planning MRI after 8 weeks of neoadjuvant ADT, and the lesions were now PIRADS 3 and prostate had shrunk. Couldn’t use the new MRI for GTV delineation bc they were indistinct and couldn’t use the old one either because the gland had shrunk. N=1 but it discouraged me from doing this routinely

I try pretty hard to not do neoadjuvant ADT. Intermediate risk hard no, data shows it is worse. High-risk can be tougher but there's no advantage of nADT (just no detriment) despite what the conclusion of RTOG 9413 tries to say ignoring the K/M curve. There are a number of patients I meet who either do not have a sufficiently delineatable lesion or their highest Gleason score doe snot correlate to where the MRI defined PI-RADS lesion is. Percentage of patients who end up getting a FLAME boost is probably in the 50-66% so good chunk are not good candidates either due to inability to get a MRI (or good quality MRI), inability (for radiology, not for me, I dont' have hubris that I can look at an MRI and define the right thing as Tyler Seibert's recent study showed) to define a PI-RADS 4/5 lesion, and/or lack of concordance between PI-RADS lesion and biopsy result.

To answer your Q, I think getting a repeat MRI after 4 months of ADT is probably worthwhile if they had an otherwise 'boostable' lesion upfront. If you can't see it anymore convincingly, then don't do a boost at all would be my approach.

Sounds like everyone is not aiming for perfection with GTV delineation and just getting the general area. Anyone not doing this with fiducials? I have really good therapists and find that we’re almost always able to get the prostate aligned. It’s the SVs that are more the problem.

Whether I am FLAME boosting or not is not a decision point in whether I use fiducials, or SpaceOAR.

I don't feel like we need fiducials, so we usually don't use them. For high risk PCa I do FLAME and do use SpaceOAR, but no fiducials.

For intermediate- or low-risk PCa, I lay out allllllll the fractionation schedules available and talk about how giving more dose per treatment does indeed increase urinary toxicity. Most patients choose SBRT despite knowing the data.

Recent data showed PSMA PET might be better than MRI for boost target delineation, so I may switch to that.

Link to bolded? Would be interesting. We currently use a hybrid approach of MRI and PET but just PET would be certainly easier... MRI would still be necessary for accurate urethral delineation however.

 

[evilbooyaa]

I am not sure you need fiducials with spaceoar?

With Vue, probably not. We still do SpaceOAR + Fiducials for SBRT but for patients w/ other fractionation schemes that request SpaceOAR (I don't feel it's necessary w/ CF or MHF regimens), if it's VUE I don't bother with fiducials.

 

[OTN]

100+ if in 44Fx to be equivalent EQD2 wise to 95Gy in 35 fractions. It's routinely not covered well due to respect urethra or rectum tolerances. If I can get 50% of the GTV getting that I'm happy.

FLAME is data of bPFS benefit with isotoxicity. It's hard to argue against beyond just 'I'm uncomfortable with it'. FLAME showed that it worked well and was tolerated well. MSK took whole gland to 86.4, and yeah they said it was OK, but I'm always skeptical that everything at MSKCC does perfectly well with no toxicity on their single institution analyses.

If most lesions are posterior and abutting the rectum, then that's unfortunate and I agree, keep the treatment isotoxic. But I think FLAME showed most lesions were getting like 50% of GTV safely getting that dose. And even that does help.

2mm PRV for urethra very reasonable. What are your urethral constraints in the 44Fx space? You're saying you limit urethra to Rx dose and accept underdosing of central prostate?

FLAME boosting does not require a spacer. Yes, in patients with posterior lesions who get FLAME boost it may help to allow more of the GTV to get better coverage with the boost, but not necessary.

I appreciate the discussion and I don't mean to come off as critical. I'm just saying if you're doing contemporary margins on prostate cancer (5mm) or less, you are in a better position than you think to do FLAME.

You're absolutely right that what is planned is not what's delivered. I frequently export an IDL to the CBCT and instruct therapists to ensure that the rectum is not within that line. It's usually not the whole gland Rx dose but maybe 105% of that (so like 105% of 79.2Gy).

Hip implants can definitely be an issue especially with older CBCTs, especially if bilateral, and if a majority of your patients have b/l hip replacements, then sure, you have a different population than me and maybe FLAME is inappropriate for them. B/L hip implants in a patient with routine constipation issues and inability to empty his rectum despite development of a laxative schedule is not a great candidate for a FLAME boost.

I will say that I am aggressive about max rectal anterior/posterior dimensions at CT sim and for treatment. Ideal < 3cm, and I won't accept sim at > 4cm unless it's at least the second day we've tried the sim. Treatment a bit more flexible, but again, keeping some isodose line out of the rectum.

I am not aware of a medicolegal case in this realm. You have good defense by saying you were following the FLAME regimen, IMO, but I know I won't convince you otherwise of that.



I try pretty hard to not do neoadjuvant ADT. Intermediate risk hard no, data shows it is worse. High-risk can be tougher but there's no advantage of nADT (just no detriment) despite what the conclusion of RTOG 9413 tries to say ignoring the K/M curve. There are a number of patients I meet who either do not have a sufficiently delineatable lesion or their highest Gleason score doe snot correlate to where the MRI defined PI-RADS lesion is. Percentage of patients who end up getting a FLAME boost is probably in the 50-66% so good chunk are not good candidates either due to inability to get a MRI (or good quality MRI), inability (for radiology, not for me, I dont' have hubris that I can look at an MRI and define the right thing as Tyler Seibert's recent study showed) to define a PI-RADS 4/5 lesion, and/or lack of concordance between PI-RADS lesion and biopsy result.

To answer your Q, I think getting a repeat MRI after 4 months of ADT is probably worthwhile if they had an otherwise 'boostable' lesion upfront. If you can't see it anymore convincingly, then don't do a boost at all would be my approach.


Whether I am FLAME boosting or not is not a decision point in whether I use fiducials, or SpaceOAR.


Link to bolded? Would be interesting. We currently use a hybrid approach of MRI and PET but just PET would be certainly easier... MRI would still be necessary for accurate urethral delineation however.

Let me see if I can find the study. Just came across it in the last day or two so hopefully will be able to find it.

My rationale for placing a SpaceOAR for FLAME was that if I truly believe the boost dose is helpful, I want to try to get good coverage to the boost volume as possible, and the boost dose does indeed cross my level of comfort for rectal dosing.

 

[HolySmokes]

https://www.thegreenjournal.com/article/S0167-8140(23)09377-5/fulltext

 

[ramsesthenice]

https://www.thegreenjournal.com/article/S0167-8140(23)09377-5/fulltext

Thanks for sharing. I am honestly a bit surprised be the results. There are so many variables, but in my personal experience, I feel like I see a lot of folks with fairly indistinct lesions in the prostate gland on PYL scans. I would have expected MRI to be better. Fortunately, I excel at taking bad guesses and making myself look smart . Here is good evidence we are not quite as good at defining the gross lesions as we think. My quadrant approach may have a rationale basis