Use of Microboost

[TheWallnerus]

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Do I think everyone getting a microboost (or SBRT) needs a spacer. Again, nope. Look at their anatomy and honestly ask yourself how at risk a patient really is for significant rectal injury. If it’s average or low, a spacer probably won’t do anything.

Has it been shown that in those with infaust rectal DVHs that a spacer improves rectal toxicity outcomes? That is to say a study where those with iffy or bad rectal DVHs went on to treatment w/ best optimized planning after initial sim versus getting spacer'd and re-simm'd and re-planned. (Of course LOGICALLY this should result in decreased rectal toxicity, but again the DVH doesn't seem to predict who gets spacer benefit based on the literature, and microboost is isotoxic, etc.)

Is that your approach with spacer... spacer decision only after initial sim and plan? "Look at their anatomy and honestly ask yourself how at risk a patient really is for significant rectal injury." Eyeballing/going with your gut alone is not enough, right? Need DVH?

 

[Barcelona PSG]

I have used both gel and balloon (Bioprotect) spacers in select cases and have moved to Bioprotect exclusively given its favorable risk profile. Still i do it only for pts on chronic anticoagulation, IBS, Crohn's or UC and in patients with prior pelvic radiation if feasible.

 

[TheWallnerus]

We would have never had a clinical benefit to IMRT in prostate if balloons/spacers etc had existed prior to IMRT

Thank god IMRT existed first or we might have never had IMRT

 

[drowsy12]

Yeah I’m not sure what wallnerus is on re this

 

[TheWallnerus]

Yeah I’m not sure what wallnerus is on re this

I’m saying if you’re a spacer user, why use it selectively. Perhaps there is no explanation and is more vibe based or get a tingly feeling or something. The DVH metrics from spacer studies don’t necessarily predict who benefits, and the microboost data (maybe even the SBRT data etc) suggests increased dose is not detectably harmful. Rectal toxicity can be a stochastic phenomenon; ergo, to get the most benefit from spacers, one would need to use it whenever irradiating. If spacers had ~zero complication risk and ~zero patient complaints, I’d use them on every XRT patient.

 

[WildRivers]

Yeah I’m not sure what wallnerus is on re this

Seriously I don’t understand the logic or what is being said. We know he’s anti-spacer. And there is some (a lot?) level of sarcasm. But I truly don’t get it. I know the Wallnerus, he is a smart fella. It’s appears to be some Andy Kauffman - esque style bit, that’s my best guess.

yet, I get pulled in

He says if you’re going to use, use on all, because of the study, but I know him pretty well. He doesnt believe that dose is the best dose for toxicity, so he would not use it. He is very good at Dosimetry and so would have a high dose constraint for rectum, but this study doesn’t have that. He uses tight margins for prostate - tighter than my own practice. He doesn’t take into account all the other studies with modern treatment that show lower toxicity.

Yet, all of that is ignored because focusing on the fact that the study was positive for all comers. We are not allowed to be skeptical of that - we have to believe that even in our practices where we perhaps different doses, tighter constraints, different margins - that none of this matters at all and that if we ever consider spacers, we are wrong to consider any of these other factors and instead act as automatons. Even though he himself has used ingenuity and his intellect to modify the way he treats and improve outcomes, in this one specific case he feels you cannot tweak or modify.

Andy K would be proud! And instead of laughing, he would give you his best and most neutral “that’s funny”.

 

[TheWallnerus]

he is a smart fella.

As smart as I am I can’t predict toxicity with 100% accuracy; no one can, although DVHs improve the ability to do so. But I can predict that a spacer would decrease rectal toxicity risk every time (properly) placed. Rectal spacer decreasing rectal toxicity is almost tautological.

focusing on the fact that the study was positive for all comers

Not “focusing.” But by their nature positive studies are positive for all comers (in that study).

The “number needed to space” applies to the population… not to an identifiable individual beforehand. We generally cannot say with confidence this is the man who would have developed rectal toxicity without a spacer, so he should get one, while safely excluding another man as someone who would derive no benefit.

If that first phIII spaceoar study had been negative spacers likely wouldn’t even exist right now (would have never gotten insurance coverage… and that coverage is for all comers).

I am way more automaton than artiste. When there’s a positive trial establishing a standard of care and I can easily implement it in practice, I check my brain at the door and become a cook following a recipe. I think that’s the right thing to do versus trying to predict the future. There are some stage III NSCLC eg that I really wanna dose escalate to 70 Gy or higher. I don’t.

We know he’s anti-spacer

No just perhaps irrationally malpractice averse and would get really stressed out over a significant spacer complication. Not using spacers has been really drama free. But if spacing was ~risk free…

 

[FletchersGarb]

I'm not a big spacer believer, but unplanned analysis of GU-005 (55% got spacer) showed bowel AE benefits - do what you want with this info.

https://jamanetwork.com/journals/jama/fullarticle/2852845

 

[evilbooyaa]

I microboost all that I can (meaning biopsy/MRI/PET as appropriate line-up).

FLAME treamtents are meant to be isotoxic, so same coverage requirements. I do ensure urethra is contoured and constrained to generally point dose < 105% of the whole gland dose.

Goal is to get at least 50% of GTV covered by boost dose.

I do not do spacer more for this. I still do not think spacer/fiducials is necessary for non-SBRT prostate.