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re-irradiation after single fraction cavity SRS? What dose?

Kroll2013

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Dear colleagues,
please advise concerning this patient:
40 yo male, high PS, diagnosed a couple of years ago of colic cancer that was locally treated.
Aug 2019: he was diagnosed of left parietal (at the level of the motor strip) solitary brain lesion.
octobre 2019: he underwent a complete resection , followed by cavity SRS 18Gy /1 fr
April 2020: refractory seizures
MRI showed a relapsing left parietal cavity lesion, whose epicenter was next to the trolard vein.
he was re-resected quasi completely.
he needs adjuvant re-RT to the new cavity , especially that there was remaining enhancement 1 mo after the surgery.
what dose do you recommend almost 6 mo after the first SRS, to minimize the risk of radionecrosis?
and how do you do the calculation ? do you add BED old prescription to BED new prescription ? and what is the threshold?


thank you a lot.
 
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Neuronix

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I invited an expert guest speaker to speak at a conference once about this very issue. I learned that there is very little data.

What is resected quasi completely?

In these cases I typically treat gross disease only. If there's no gross disease I wait for it to grow back.

Also, I fractionate these cases based on no data but a belief that it might be safer.

5 Gy x 5 fractions is safe but probably too little--I usually do 6 Gy x 5 fractions with 0-1 mm margin to gross disease only. Can also consider 5 Gy x 5 fractions to cavity with dose paint 6 Gy x 5 to gross disease.
 
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evilbooyaa

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I don't like adjuvant RT in the re-SRS setting. Would not treat entire cavity.

I hate, hate, hate re SRSing in only a 6 month time frame.

If pushed to treat I would do something like 7-8Gy x 3 to residual disease only.

My personal preference would be to watch this closely with q2 month MRIs and treat at sign of progression. I feel that benefits vs risks of repeat SRS in this are not in the right balance. Gives you sometime to 'kick the can down the road' and allow for some potential recovery of brain.
 
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RickyScott

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I don't like adjuvant RT in the re-SRS setting. Would not treat entire cavity.

I hate, hate, hate re SRSing in only a 6 month time frame.

If pushed to treat I would do something like 7-8Gy x 3 to residual disease only.

My personal preference would be to watch this closely with q2 month MRIs and treat at sign of progression. I feel that benefits vs risks of repeat SRS in this are not in the right balance. Gives you sometime to 'kick the can down the road' and allow for some potential recovery of brain.
I have had 2-3 cases where I fractionated with 15 x 267.
 
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StIGMA

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There is no rush to treat. Would closely observe (q4-6wk). If what is apparently residual disease grows on serial scans (at least one scan, preferably 2 scans if symptoms not worsening), I would treat focally based on size criteria. I don't see a strict need to fractionate in this case if the gross disease volume is small. Treating the whole cavity as above is a fine approach too but would be hesitant with location. Risk of leptomeningeal spread is high and there is a chance you may keep getting marginal recurrences, so I disfavor a 0 mm margin with cavities.
 
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Mandelin Rain

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I’ve had terrible luck SRSing cavities. I’ve had extracranial soft tissue recurrences, dural recurrences, parenchymal recurrences, leptomeingeal recurrences. I think I’m about done with it.

I like the idea of 5x5 to cavity plus wider margin with sib to gross disease.
 
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Reaganite

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I’ve had terrible luck SRSing cavities. I’ve had extracranial soft tissue recurrences, dural recurrences, parenchymal recurrences, leptomeingeal recurrences. I think I’m about done with it.

I like the idea of 5x5 to cavity plus wider margin with sib to gross disease.

Agree. Wonder what others are seeing, but I used to attend a multi-institutional neuro tumor board and it was SRS cavity recurrence after recurrence after recurrence.
 
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Palex80

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The whole concept of SRSins cavities is flawed, IMHO.

SRS is meant to include prescription to a lower isodose than 95%-100%.
You push the dose in the middle of the PTV (-->which is generally the GTV) and prescribe lower doses to the edge of the PTV, the dose fall off is steep beyond that.

When we treat cavities there is no GTV, there is only a CTV.

Guess where the risk of recurrence is at the highest? In the middle of the CTV? No. There's only "water" there.
The risk is at the highest at the edge of the CTV.

So we are prescribing higher doses to areas with lower risk of recurrence than we are at the areas with the highest risk of recurrence.

It is simply illogical to use single dose SRS when treating cavities.
 
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Kroll2013

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I don't re-SRS surgical cavities. I usually closely follow, then treat gross disease upon recurrence to help limit volume. If this was a "quasi-complete" resection, then I imagine recurrence will declare itself sooner rather than later.
what about the risk of leptomeningeal relapse?
 
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Kroll2013

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The whole concept of SRSins cavities is flawed, IMHO.

SRS is meant to include prescription to a lower isodose than 95%-100%.
You push the dose in the middle of the PTV (-->which is generally the GTV) and prescribe lower doses to the edge of the PTV, the dose fall off is steep beyond that.

When we treat cavities there is no GTV, there is only a CTV.

Guess where the risk of recurrence is at the highest? In the middle of the CTV? No. There's only "water" there.
The risk is at the highest at the edge of the CTV.

So we are prescribing higher doses to areas with lower risk of recurrence than we are at the areas with the highest risk of recurrence.

It is simply illogical to use single dose SRS when treating cavities.
I totally agree. ty
 
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evilbooyaa

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what about the risK of leptomeningeal relapse? no one can guarantee a local relapse !

Post-op SRS does not affect risk of LM relapse: Post-operative stereotactic radiosurgery versus observation for completely resected brain metastases: a single-centre, randomised, controlled, phase 3 trial

" 20 patients developed leptomeningeal disease (8 in the observation group and 12 in the SRS group). At 12 months, the incidence of leptomeningeal disease was 16% (95% CI 4–26) in the observation group and 28% (12–40) in the SRS group (HR 1·4 [95% CI 0·6–3·4]; p=0·46). 19 of the 20 patients with leptomeningeal disease subsequently had WBRT (8 in the observation group and 11 in the SRS group). "


I have, at times, felt that we need to stop doing post-op SRS and just monitor for recurrence. I feel more and more like that everyday it seems like.

Let's talk about a 50% rate of recurrence with surgery alone, with no effect on overall survival or other functional endpoints.

For brain mets (where patients have metastatic disease) we advocate adjuvant treatment.

But, for prostate cancer (where patients don't have metastatic disease), we advocate waiting and treating at recurrence.

Both scenarios have equal efficacy (in terms of OS) regardless of whether you do adjuvant or salvage. Why do we treat them differently?
 
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radiation

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Post-op SRS does not affect risk of LM relapse: Post-operative stereotactic radiosurgery versus observation for completely resected brain metastases: a single-centre, randomised, controlled, phase 3 trial

" 20 patients developed leptomeningeal disease (8 in the observation group and 12 in the SRS group). At 12 months, the incidence of leptomeningeal disease was 16% (95% CI 4–26) in the observation group and 28% (12–40) in the SRS group (HR 1·4 [95% CI 0·6–3·4]; p=0·46). 19 of the 20 patients with leptomeningeal disease subsequently had WBRT (8 in the observation group and 11 in the SRS group). "


I have, at times, felt that we need to stop doing post-op SRS and just monitor for recurrence. I feel more and more like that everyday it seems like.

Let's talk about a 50% rate of recurrence with surgery alone, with no effect on overall survival or other functional endpoints.

For brain mets (where patients have metastatic disease) we advocate adjuvant treatment.

But, for prostate cancer (where patients don't have metastatic disease), we advocate waiting and treating at recurrence.

Both scenarios have equal efficacy (in terms of OS) regardless of whether you do adjuvant or salvage. Why do we treat them differently?

Depends on your viewpoint on relapse in the brain and how often you image. Relapse in the prostate is almost never symptomatic or takes a very long time to be symptomatic. Proponents of whole brain like Bill Regine would say that the incidence of symptomatic progression in the brain from new brain mets is high enough that it justifies whole brain radiation in certain situations. Likewise, progression in a cavity can potentially symptomatic. A temporal lobe relapse can be very symptomatic if it causes seizures at progression.

We dont really have the equivalent data in brain that says early salvage radiosurgery has same success rate and/or toxicity as adjuvant cavity because there is no equivalent that is as sensitive or cheap as PSA. Most people do MRI q 3 months, which can be a long time for a tumor to grow into a cavity. If its just a small nodular relapse salvage SRS is pretty easy. But not all of them relapse this way and if you have multiple nodules over time in the same cavity it can get tricky. Hard to talk about OS in Mahajan trial because numbers too small and very few brain studies powered for that analysis. Patchell 2 did show a survival benefit with whole brain radiation after resection and the N107C Alliance study trended better for whole brain. None powered for OS as mentioned.

Shockingly, the one part that N107C study buried was that local control was also worse in the cavity group, which was very counterintuitive. Many actually argue that the group of patients we most associate with SRS (young, healthy, well-controlled extracranial disease) are probably the ones that would benefit from whole brain the most from an OS standpoint (because their life-limiting disease may be in the brain). Double the intracranial brain control at 12 months with whole brain (vs cavity).

1590693692844.png
 
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