Hippocampal avoidance

[Pointless]

Randomized phase III evidence shows us this is superior to conventional WBRT. Is this standard of care now? What has been the experience with insurers for those who have been doing this already?

Hippocampal Avoidance During Whole-Brain Radiotherapy Plus Memantine for Patients With Brain Metastases: Phase III Trial NRG Oncology CC001 - PubMed

HA-WBRT plus memantine better preserves cognitive function and patient-reported symptoms, with no difference in intracranial PFS and OS, and should be considered a standard of care for patients with good performance status who plan to receive WBRT for brain metastases with no metastases in the...

www.ncbi.nlm.nih.gov

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[deleted941485]

Randomized phase III evidence shows us this is superior to WBRT. Is this standard of care now? What has been the experience with insurers for those who have been doing this already?

Hippocampal Avoidance During Whole-Brain Radiotherapy Plus Memantine for Patients With Brain Metastases: Phase III Trial NRG Oncology CC001 - PubMed

HA-WBRT plus memantine better preserves cognitive function and patient-reported symptoms, with no difference in intracranial PFS and OS, and should be considered a standard of care for patients with good performance status who plan to receive WBRT for brain metastases with no metastases in the...

www.ncbi.nlm.nih.gov

I brought this up a few days ago and got blank stares like I was from mars. I really hate my colleagues.

 

[Burt Radnolds]

I just saw this through Doximity and it is compelling data. I will definitely be more likely to consider it going forward but don't have personal experience battling insurers. However, we do so much SRS (can't avoid the hippcampus much more than that) that by the time patients are candidates for whole brain they don't have the life expectancy to justify it. Curious to hear others thoughts as well.

 

[Pointless]

I brought this up a few days ago and got blank stares like I was from mars. I really hate my colleagues.

I'll admit that I was a skeptic.. but the data is what it is. Do you work with boomers?

 

[Pointless]

I just saw this through Doximity and it is compelling data. I will definitely be more likely to consider it going forward but don't have personal experience battling insurers. However, we do so much SRS (can't avoid the hippcampus much more than that) that by the time patients are candidates for whole brain they don't have the life expectancy to justify it. Curious to hear others thoughts as well.

Ditto re: SRS/SRT. This will mainly be for small cell patients or the few with innumerable mets not amenable to SRS.

 

[deleted941485]

I'll admit that I was a skeptic.. but the data is what it is. Do you work with boomers?

How can anyone not work with them?

 

[Pointless]

How can anyone not work with them?

LOL touche. I guess in a small practice you could work with only more recent grads. But yes, they seem to be ubiquitous.

 

[StIGMA]

I just saw this through Doximity and it is compelling data. I will definitely be more likely to consider it going forward but don't have personal experience battling insurers. However, we do so much SRS (can't avoid the hippcampus much more than that) that by the time patients are candidates for whole brain they don't have the life expectancy to justify it. Curious to hear others thoughts as well.

We are doing a very reasonable volume of hippocampal avoidance on and off trial for WBRT. With SRS, I routinely contour the hippocampus and constrain mean <4 Gy (or whatever is reasonable given target volumes/locations). We do a lot of repeat SRS and we have several patients ECOG 0 or 1 >5years out of initial SRS (some >10 years with lung adenocarcinoma, others) that it seems reasonable to keep honing how we approach things (one small step at a time, with the impetus on the rest of the oncology world realizing what we can accomplish).

 

[Palex80]

Well, the Dutch trial failed to show any benefit in SCLC patients undergoing PCI with or without hippocampal avoidance.

The Dutch trial is smaller but their follow up is longer.


We used to perform PCI with hippocampal avoidance up until the Dutch trial results showed up and dropped it then. I am not sure what to do now...
Indications for WBRT (excluding PCI for SCLC) have been declining in the past years rapidly, since we give a lot more stereotactic treatments nowadays and those few patients that we give WBRT to usually have such an unfavorable prognosis that they would probably not live enough to experience any benefit from hippocampal avoidance. Sadly, a big part of those patients are the ones we shouldn't be irradiating at all, but that's another story...

 

[FrostyHammer]

TBH I use SRS as a means to perform hippocampal sparing, but I agree with the above that the larger the number of mets and the higher risk of developing more mets is a major consideration. Doing repeat SRSes isn't bad, it's just a pain to keep track of which mets were zapped before and which need to be zapped now...

 

[Haybrant]

LOL touche. I guess in a small practice you could work with only more recent grads. But yes, they seem to be ubiquitous.

How can anyone not work with them?

Document the clearly wrong things they do and then report them to. The board

 

[scarbrtj]

We should do IMRT for all whole brain met patients (ie doses of 30 Gy or more), because HA works. End of discussion!

We should never do IMRT for whole brain PCI patients (ie doses of 25 Gy or so), because HA doesn't work. Beginning of discussion!
(EDIT: what Palex said!)

 

[PhotonBomb]

to build off of what scarb said and to address pointless' question - my guess is that hippocampal avoidance will be fine now (the excuse evicore used over past year was ABSTRACT ONLY NEED TO WAIT FOR PAPER) so that excuse is over.

HOWEVER, good luck trying it in PCI patients, because there is conflicting data in small cell PCI, and untill NRG CC003 gets PUBLISHED (not presented y'all, published) you won't be able to get away with it. of course that is assuming CC003 is a positive trial for PCI. we will see.

FIN.

 

[taserlaser]

HA-WBRT is also being compared with SRS in CE7 - Stereotactic Radiosurgery Compared With Hippocampal-Avoidant Whole Brain Radiotherapy (HA-WBRT) Plus Memantine for 5-15 Brain Metastases - Full Text View - ClinicalTrials.gov

I agree that the number of patients this is applying to is getting smaller and smaller...

 

[Palex80]

We should do IMRT for all whole brain met patients (ie doses of 30 Gy or more), because HA works. End of discussion!

We should never do IMRT for whole brain PCI patients (ie doses of 25 Gy or so), because HA doesn't work. Beginning of discussion!
(EDIT: what Palex said!)

We are doing VMAT for WBRT, but without hippocampal avoidance...

*S***storm inbound...*

 

[PhotonBomb]

We are doing VMAT for WBRT, but without hippocampal avoidance...

*S***storm inbound...*

i mean you can cuz you're in the soviet bloc or europe or wherever you are. people will prob do this all the time in the US if they feel like putting the extra work in and think there's a point to it when APM comes.

APM will set us all free.

 

[Palex80]

i mean you can cuz you're in the soviet bloc or europe or wherever you are. people will prob do this all the time in the US if they feel like putting the extra work in and think there's a point to it when APM comes.

APM will set us all free.

I'm in Europe. Soviets disappeared 20 years ago.

 

[scarbrtj]

And on another note, echoing somewhat what you guys have said, if we (have the ?hubris? that we) can measure the statistically significant clinical effect of this:

sparing 4 cubic centimeters of brain in a ~1400 cubic centimeter brain (ie ~0.3% organ sparing!)...

just think what the clinical effects that ~100% organ sparing can achieve. (I'm not a neurologist, but I bet [brain minus hippocampus] is more important than [hippocampus]? Also, when you look at the volume spared in hippocampal sparing, my back-of-envelope calc would say you might need ~2500-5000 patients in each arm to measure a difference in failure rates "caused" by HA.)

 

[PhotonBomb]

 

[Neuronix]

I'm so over cost-effectiveness at this point. I even tried to submit a grant on cost-effectiveness, and there's nowhere to even send them anymore because even our government doesn't seem to care.

The entire cancer enterprise is so far from cost-effective healthcare that I'm just taking a patient perspective at this point. Will insurance pay for it? Might there be benefit? I have patients out several years from WBRT. Sure it's a minority, but looking at a lot of my patients I don't know who that will be. If I do VMAT whole brain and give the patient memantine, that's a drop in the bucket compared to all these expensive immunotherapies and targeted agents my patients are getting.

Randomized phase III evidence shows us this is superior to conventional WBRT. Is this standard of care now? What has been the experience with insurers for those who have been doing this already?

Hippocampal Avoidance During Whole-Brain Radiotherapy Plus Memantine for Patients With Brain Metastases: Phase III Trial NRG Oncology CC001 - PubMed

HA-WBRT plus memantine better preserves cognitive function and patient-reported symptoms, with no difference in intracranial PFS and OS, and should be considered a standard of care for patients with good performance status who plan to receive WBRT for brain metastases with no metastases in the...

www.ncbi.nlm.nih.gov

I'd argue that it's standard of care now. In fact, I'd argue that hippocampal avoidance has been a reasonable option ever since the phase 2 trial. The PIs of the CC001 study argued that it should not be considered standard of care at that point, and to enroll on their phase 3 tudy, which I did as much as possible.

I'd say that insurance resistance has been diminishing over the years. It seems like it used to be a coinflip whether I could get it covered 3 years ago, whereas now I meet little resistance.

I brought this up a few days ago and got blank stares like I was from mars. I really hate my colleagues.

If you convert them, get ready to train them in how to draw the hippocampus, the dosimetrists in how to generate the plans, and how to prescribe memantine.

I just saw this through Doximity and it is compelling data. I will definitely be more likely to consider it going forward but don't have personal experience battling insurers. However, we do so much SRS (can't avoid the hippcampus much more than that) that by the time patients are candidates for whole brain they don't have the life expectancy to justify it. Curious to hear others thoughts as well.

I feel similarly on this. My number of patients getting whole brain is shrinking because SRS is getting so easy to deliver. I'm randomizing on CE.7 trial, but off trial I have no problem with 15 small brain mets.

We are doing VMAT for WBRT, but without hippocampal avoidance...

*S***storm inbound...*

Why? What are you sparing? Or is it just to keep down hot spots? I do 3D with "field-in-field" optimization routinely to minimize hot spots, so we may not be in disagreement here.

HOWEVER, good luck trying it in PCI patients, because there is conflicting data in small cell PCI, and untill NRG CC003 gets PUBLISHED (not presented y'all, published) you won't be able to get away with it. of course that is assuming CC003 is a positive trial for PCI. we will see.

I just don't do PCI any more.

*S***storm inbound...*

 

[Palex80]

Why? What are you sparing? Or is it just to keep down hot spots? I do 3D with "field-in-field" optimization routinely to minimize hot spots, so we may not be in disagreement here.

The parotid glands.
Not that one cannot spare those with 3D-techniques too, but you asked what we are sparing.

Basically, it has become easier for our dosimetrists to make a VMAT plan and we get paid the same, irrelevant of the technique, so we just do it.

 

[Palex80]

I just don't do PCI any more.
*S***storm inbound...*

 

[Neuronix]

The parotid glands.
Not that one cannot spare those with 3D-techniques too, but you asked what we are sparing.

Basically, it has become easier for our dosimetrists to make a VMAT plan and we get paid the same, irrelevant of the technique, so we just do it.

Ah! Good thought.

What's your inferior field border? With opposed lateral technique it seems to me that the parotids don't get much dose if you go to C1-C2 interspace. If you go to C2-C3 you end up with half the parotid gland in the field, depending on how tight you are on the front of the vertebral bodies.

View attachment 296552

You have out-memed me good sir.

This article lays out the arguments that led to the recently opened SWOG S1827 trial Prophylactic Cranial Irradiation (PCI) versus Active MRI Surveillance for Small Cell Lung Cancer: The Case for Equipoise

We can argue both sides of this, and we have done so on this forum before. I guess we'll know in a few years, maybe.

 

[Palex80]

This article lays out the arguments that led to the recently opened SWOG S1827 trial Prophylactic Cranial Irradiation (PCI) versus Active MRI Surveillance for Small Cell Lung Cancer: The Case for Equipoise

We can argue both sides of this, and we have done so on this forum before. I guess we'll know in a few years, maybe.

All good arguments. But until the trial is done, shouldn't we stick to the good old standard of care. You know, the one that's actually proven by a few trials to actually SAVE people's lives and improved their already miserable prognosis by around 5% in absolute terms or 20% in relative terms?

 

[deleted1002574]

Not one of those studies used MRI staging. PCI is treating Asymptomatic brain mets in unstaged SCLC.

All good arguments. But until the trial is done, shouldn't we stick to the good old standard of care. You know, the one that's actually proven by a few trials to actually SAVE people's lives and improved their already miserable prognosis by around 5% in absolute terms or 20% in relative terms?

 

[Neuronix]

All good arguments. But until the trial is done, shouldn't we stick to the good old standard of care. You know, the one that's actually proven by a few trials to actually SAVE people's lives and improved their already miserable prognosis by around 5% in absolute terms or 20% in relative terms?

The data for LS-SCLC is from meta-analyses from before routine MRI surveillance was a thing. ED-SCLC surveillance vs. PCI was repeated by the Japanese and it was negative.

Whole brain radiation is a really tough sell even when patients really need it. When I tried to sign up patients for NRG CC003, my patients almost uniformly said "whole brain radiation is horrible. I refuse this trial, and I refuse whole brain radiation entirely." I've had patients with active brain mets die of brain disease because they were so afraid of whole brain radiation despite hours of my time trying to convince them otherwise. I have a patient right now with leptomeningeal disease who got 5 different opinions from 4 different centers because she really does not want whole brain. I had another patient last month who was crying and almost hospitalized for psychiatric reasons because she had leptomeningeal disease and was convinced that whole brain radiation would take away all her mental processes and kill her within 2 weeks of receipt of the treatment.

So yeah, it's a combination of this being a battle I'm not really willing to fight, and also a battle I don't really believe in. I could be wrong. Time will tell.

 

[RickyScott]

to build off of what scarb said and to address pointless' question - my guess is that hippocampal avoidance will be fine now (the excuse evicore used over past year was ABSTRACT ONLY NEED TO WAIT FOR PAPER) so that excuse is over.

HOWEVER, good luck trying it in PCI patients, because there is conflicting data in small cell PCI, and untill NRG CC003 gets PUBLISHED (not presented y'all, published) you won't be able to get away with it. of course that is assuming CC003 is a positive trial for PCI. we will see.

FIN.

I have done a few pci pts and had it approved.

 

[Palex80]

Not one of those studies used MRI staging. PCI is treating Asymptomatic brain mets in unstaged SCLC.

Indeed, MRI was not used.
Yet you cannot really know if all patients that benefitted had macroscopic metastasis at the point of randomization.

Actually, I think this is not the answer, because the trials showed a survival benefit with a tail of long-term survivors that was in the range of 5% higher in absolute terms than without PCI.

Can you really control a macroscopic metastasis that you would have picked up with an MRI if you only give 30/2 or 25/2.5?

Even if it's SCLC it would be a metastasis that has already "survived" 4 cycles of cisplatin-based chemotherapy and you want to tell me that you are going to completely cure it with 25-30 Gy of fractionated treatment? I don't think so...

The long-term survival benefit came from treating asymptomatic, microscopic brain metastases in those patients.


I am advocating for PCI only in the setting of limited-disease SCLC.
I don't give PCI for ED-SCLC but will fight for it for most LD-SCLC patients I see.
Observation and treatment for recurrence with SRS is not proven in this patients group in my opinion.

 

[scarbrtj]

Why? What are you sparing? Or is it just to keep down hot spots? I do 3D with "field-in-field" optimization routinely to minimize hot spots, so we may not be in disagreement here.

The parotid glands.
Not that one cannot spare those with 3D-techniques too, but you asked what we are sparing.

Basically, it has become easier for our dosimetrists to make a VMAT plan and we get paid the same, irrelevant of the technique, so we just do it.

What's your inferior field border? With opposed lateral technique it seems to me that the parotids don't get much dose if you go to C1-C2 interspace. If you go to C2-C3 you end up with half the parotid gland in the field, depending on how tight you are on the front of the vertebral bodies.

What you get with any approach that's >2 field (which VMAT obv is e.g.) WBRT is: 1) less scalp dose (and so less desqu, gr 1 esp), 2) less of those behind-ear red, itchy spots, and 3) a little more potential for less hair loss. It's like with a 2-field vs 3-field (vs multifield) pelvis: less desqu potential with >2 fields. And it is easier to minimize intracranial inhomogeneity (could have done better than ~110% max, usu aim for ~107% max). You can do 3 fields, not FiF (which is IMRT too heh), but "full monty" IMRT. And you can spare the parotids without even trying (they're in light green on the DVH, the smallest DVH curve... honestly have never considered them), and it's much faster to calc and plan than VMAT. And about as fast as 2 field. On-treatment-table time just expands by that one extra field too. I have never been compelled (or seen evidence it's necessary) to do WBRT plus a tiny bit of spinal cord (ie inf border at C1/2 or C2/3), so I just always keep the inferior border at the foramen magnum.

To each his or her own though.

 

[RickyScott]

What you get with any approach that's >2 field WBRT is: 1) less scalp dose (and so less desqu, gr 1 esp), 2) less of those behind-ear red, itchy spots, and 3) a little more potential for less hair loss. It's like with a 2-field vs 3-field (vs multifield) pelvis: less desqu potential with >2 fields. And it is easier to minimize intracranial inhomogeneity (could have done better than ~110% max, usu aim for ~107% max). You can do 3 fields, not FiF (which is IMRT too heh), but "full monty" IMRT. And you can spare the parotids without even trying (they're in light green on the DVH, the smallest DVH curve... honestly have never considered them), and it's much faster to calc and plan than VMAT. And about as fast as 2 field. On-treatment-table time just expands by that one extra field too. I have never been compelled (or seen evidence it's necessary) to do WBRT plus a tiny bit of spinal cord (ie inf border at C1/2 or C2/3), so I just always keep the inferior border at the foramen magnum.

To each his or her own though.

Waiting for obligate idiot to express concern about integral dose or 2nd malignancies in whole brain pt? Or cataracts?

 

[deleted1002574]

A wise man said "If you do whole brain and they live long enough to get cataracts, you've done right by this patient ... "
(I said that)

 

[scarbrtj]

Waiting for obligate idiot to express concern about integral dose or 2nd malignancies in whole brain pt? Or cataracts?

Lens dose just the same (maybe milligray differences) with 2 field or 3 (about 2 Gy or less), as they're 100% out-of-beam either way. "Integral dose"... maybe less with 3 field, if we mean AUC "body." Because you can let the algorithm minimize the "virtual block edge-to-target" distance better with IMRT than hard-margin-3D-blocking, if that makes sense, and less inhomo w/3 vs 2 field. So I'm gonna guess 3 field wins even w/ AUC. I think I looked at this aeons ago.

 

[evilbooyaa]

Ditto re: SRS/SRT. This will mainly be for small cell patients or the few with innumerable mets not amenable to SRS.

SCLC patients were specifically excluded from this study. As were folks with Leptomeningeal disease.

We offer it for good KPS patients w/o Leptomeningeal dz or SCLC histology to all patients who don't have a lesion within 5-10mm of the hippocampus.

We do it for those who have more than 10-15 brain mets as we are otherwise SRS'ing everybody below that number.

We will plan to enroll on SWOG trial when it eventually opens but we will currently offer observation off-protocol, with a description that the SOC is still to get PCI.

 

[Neuronix]

SCLC patients were specifically excluded from this study. As were folks with Leptomeningeal disease.

Funnily enough, the next trial for SCLC brain mets is going to be HA-WBRT vs. SRS. Why HA-WBRT? Because the brain met Illuminati says it's ok. Well, guess what, I'm doing it too.

We offer it for good KPS patients w/o Leptomeningeal dz or SCLC histology to all patients who don't have a lesion within 5-10mm of the hippocampus.

We do it for those who have more than 10-15 brain mets as we are otherwise SRS'ing everybody below that number.

You can do it CE.7 style and still spare the uninvolved hippocampii if you really want. Yes, I do this off protocol. It's not my fault that over 50% of my patients are not fluent English (or French Canadian) speakers and aren't eligible for CE.7.

We will plan to enroll on SWOG trial when it eventually opens but we will currently offer observation off-protocol, with a description that the SOC is still to get PCI.

SWOG trial is open.

 

[Pointless]

SCLC patients were specifically excluded from this study. As were folks with Leptomeningeal disease.

We offer it for good KPS patients w/o Leptomeningeal dz or SCLC histology to all patients who don't have a lesion within 5-10mm of the hippocampus.

We do it for those who have more than 10-15 brain mets as we are otherwise SRS'ing everybody below that number.

We will plan to enroll on SWOG trial when it eventually opens but we will currently offer observation off-protocol, with a description that the SOC is still to get PCI.

Did it? I have been looking at the protocol and I see the eligibility criteria as anyone with a solid malignancy. Perhaps I need to look closer at the exclusion criteria.

Anyway, yes, I would never contemplate this in anyone with mets near that HA zone.

 

[evilbooyaa]

Did it? I have been looking at the protocol and I see the eligibility criteria as anyone with a solid malignancy. Perhaps I need to look closer at the exclusion criteria.

Anyway, yes, I would never contemplate this in anyone with mets near that HA zone.

3.3.10 Below - From the protocol obtainable from the supplement of the JCO publication.

And we generally use 5mm as a cut-off, although if it is closer, we have still prescribed 30Gy to that lesion + PTV margin and can still achieve close to the dosimetric goals.

 

[Pointless]

Thanks @evilbooyaa.

 

[xrthopeful]

SCLC patients were specifically excluded from this study. As were folks with Leptomeningeal disease.

We offer it for good KPS patients w/o Leptomeningeal dz or SCLC histology to all patients who don't have a lesion within 5-10mm of the hippocampus.

We do it for those who have more than 10-15 brain mets as we are otherwise SRS'ing everybody below that number.

We will plan to enroll on SWOG trial when it eventually opens but we will currently offer observation off-protocol, with a description that the SOC is still to get PCI.

when you treat 10-15, do you do it on a linac? how many do you usually treat at a time?

 

[Neuronix]

when you treat 10-15, do you do it on a linac? how many do you usually treat at a time?

I've done both linac and GK for these cases depending on year. GK gets a little painful when it's over 3 hours. Hyperarc is like 15 minutes. I treat all in one session.

 

[RickyScott]

I've done both linac and GK for these cases depending on year. GK gets a little painful when it's over 3 hours. Hyperarc is like 15 minutes. I treat all in one session.

My record is 20. Don’t have hyper arc. Plan still comparable to gk. UAB and our favorite resident resident have published a ton on this.

 

[Neuronix]

My record is 20. Don’t have hyper arc. Plan still comparable to gk. UAB and our favorite resident resident have published a ton on this.

I've spent a lot of time comparing these technologies both for publications and for the institution. Whether single isocenter multi-lesion VMAT SRS plans are truly comparable to GK depends on a lot of factors. Specifically,

1. How good is your dosimetrist for MLC-based linac SRS? There is a large learning curve there, and I've seen groups doing it wrong with some really lousy plans because the whole enterprise just doesn't know any better what to do or what to expect in a quality plan. Hyperarc mostly takes away that factor.

2. How picky are you with the GK planning? That is, are you running Perfexion/Ikon, and if so are you making longer more conformal plans with mixed shots or just running fast plans. If you just run fast plans that aren't very conformal at baseline, the linac plans will look better.

3. How big a margin do you use for linac? GK usually has no margin. If you add 2 mm with linac then it's no longer comparable. UAB always does comparison with 0 mm PTV margin, and that's how they treat, but many groups are not comfortable with this.

4. Are you using microMLCs? 5 mm MLCs will give worse plans for small lesions.

5. How is the quality and how recent are your MRIs, and how well are they fused? If you don't pay very close attention to these factors you will easily fail no matter how you treat.

There are a few more things we can probably discuss but those are the big ones that come to mind.

 

[scarbrtj]

I've spent a lot of time comparing these technologies both for publications and for the institution. Whether single isocenter multi-lesion VMAT SRS plans are truly comparable to GK depends on a lot of factors. Specifically,

1. How good is your dosimetrist for MLC-based linac SRS? There is a large learning curve there, and I've seen groups doing it wrong with some really lousy plans because the whole enterprise just doesn't know any better what to do or what to expect in a quality plan. Hyperarc mostly takes away that factor.

2. How picky are you with the GK planning? That is, are you running Perfexion/Ikon, and if so are you making longer more conformal plans with mixed shots or just running fast plans. If you just run fast plans that aren't very conformal at baseline, the linac plans will look better.

3. How big a margin do you use for linac? GK usually has no margin. If you add 2 mm with linac then it's no longer comparable. UAB always does comparison with 0 mm PTV margin, and that's how they treat, but many groups are not comfortable with this.

4. Are you using microMLCs? 5 mm MLCs will give worse plans for small lesions.

There are a few more things we can probably discuss but those are the big ones that come to mind.

Are you trying to say the human factor is more important than the technological factor... in radiation oncology?!

 

[evilbooyaa]

when you treat 10-15, do you do it on a linac? how many do you usually treat at a time?

Always on a linac. Don't have hyperarc, so this is all rapid arc based. 2.5mm MLCs. 1mm Margin. Attending dependent. Some folks OK with single isocenter multi lesions, others prefer multi isocenters but clustering of lesions close together.

We frequently treat 2 or 3 isos per day if doing multi isocenter - sometimes that's 3 lesions, sometimes that's 8. Just depends on how close the lesions are to one another.

 

[Neuronix]

Always on a linac. Don't have hyperarc, so this is all rapid arc based. 2.5mm MLCs. 1mm Margin. Attending dependent. Some folks OK with single isocenter multi lesions, others prefer multi isocenters but clustering of lesions close together.

Is it a 6-DOF couch?

 

[evilbooyaa]

Is it a 6-DOF couch?

Yup. Only way to control for the rotational error we see. I wouldn't do single iso multi lesion without it.

 

[nkmiami]

I've spent a lot of time comparing these technologies both for publications and for the institution. Whether single isocenter multi-lesion VMAT SRS plans are truly comparable to GK depends on a lot of factors. Specifically,

1. How good is your dosimetrist for MLC-based linac SRS? There is a large learning curve there, and I've seen groups doing it wrong with some really lousy plans because the whole enterprise just doesn't know any better what to do or what to expect in a quality plan. Hyperarc mostly takes away that factor.

2. How picky are you with the GK planning? That is, are you running Perfexion/Ikon, and if so are you making longer more conformal plans with mixed shots or just running fast plans. If you just run fast plans that aren't very conformal at baseline, the linac plans will look better.

3. How big a margin do you use for linac? GK usually has no margin. If you add 2 mm with linac then it's no longer comparable. UAB always does comparison with 0 mm PTV margin, and that's how they treat, but many groups are not comfortable with this.

4. Are you using microMLCs? 5 mm MLCs will give worse plans for small lesions.

5. How is the quality and how recent are your MRIs, and how well are they fused? If you don't pay very close attention to these factors you will easily fail no matter how you treat.

There are a few more things we can probably discuss but those are the big ones that come to mind.

agree with most of what you are saying- especially point 5 re fusion accuracy (i also find contrast helps with these fusions and sometimes have seen different enhancement patterns on ct and MRI including several instances where the ct enhancement was larger than that seen on mri). For insurance and logistic reasons, getting timely spatially corrected volumetric mri can be difficult, and when this is an issue, it does sway me to add margin, and when I add margin, I fractionate. I have been using UAB approach for 4-5 years now. Do differ on extent to which micro mlcs have impact on plan for small lesions. Scarbtj probably could comment more, but with single iso vmat 1) many of lesions seeing dose delivered by larger peripheral 5mm mlcs away from the 2.5 central micromlc? 2) collimator rotations really lessen effect of mlc size. I dont have hyperarc, but would love to get it and play around with it.

 

[scarbrtj]

Always on a linac. Don't have hyperarc, so this is all rapid arc based. 2.5mm MLCs. 1mm Margin. Attending dependent. Some folks OK with single isocenter multi lesions, others prefer multi isocenters but clustering of lesions close together.

We frequently treat 2 or 3 isos per day if doing multi isocenter - sometimes that's 3 lesions, sometimes that's 8. Just depends on how close the lesions are to one another.

Is it a 6-DOF couch?

Yup. Only way to control for the rotational error we see. I wouldn't do single iso multi lesion without it.

agree with most of what you are saying- especially point 5 re fusion accuracy (i also find contrast helps with these fusions and sometimes have seen different enhancement patterns on ct and MRI including several instances where the ct enhancement was larger than that seen on mri). For insurance and logistic reasons, getting timely spatially corrected volumetric mri can be difficult, and when this is an issue, it does sway me to add margin, and when I add margin, I fractionate. I have been using UAB approach for 4-5 years now. Do differ on extent to which micro mlcs have impact on plan for small lesions. Scarbtj probably could comment more, but with single iso vmat 1) many of lesions seeing dose delivered by larger peripheral 5mm mlcs away from the 2.5 central micromlc? 2) collimator rotations really lessen effect of mlc size. I dont have hyperarc, but would love to get it and play around with it.

I get criticized for overly loquacious posts. So I will try to be succinct by way of analogy. The tilt-a-couch (how about just setting up the patient well, measuring the rot error with IGRT, and if <1° pitch/yaw/roll, don't need 6DoF couch?), the leaves, the margins, the isocenter number(s)... they are all versions of Walter White's fly. When the meth is ~99% pure, a tenth a percent either way is angels dancing on the head of a pin. Wanna chase the fly? Chase it! Wanna get the meth out? Get it out!

 

[nkmiami]

I get criticized for overly loquacious posts. So I will try to be succinct by way of analogy. The tilt-a-couch (how about just setting up the patient well, measuring the rot error with IGRT, and if <1° pitch/yaw/roll, don't need 6DoF couch?), the leaves, the margins, the isocenter number(s)... they are all versions of Walter White's fly. When the meth is ~99% pure, a tenth a percent either way is angels dancing on the head of a pin. Wanna chase the fly? Chase it! Wanna get the meth out? Get it out!

Some additional thoughts. If you want gamma knife like plans, you need to tolerate 40-50% hot spots, which is what UAB does. That could turn out to be a problem if hot spot is in ring of "normal brain" - PTV-gtv as paper from Emory recently suggested, where they related necrosis to dose>110% in this ring for fractionated treatments(disclaimer- I only read the abstract) and this could be an argument against margin. I am not sure the answer here.

 

[Neuronix]

I get criticized for overly loquacious posts. So I will try to be succinct by way of analogy. The tilt-a-couch (how about just setting up the patient well, measuring the rot error with IGRT, and if <1° pitch/yaw/roll, don't need 6DoF couch?), the leaves, the margins, the isocenter number(s)... they are all versions of Walter White's fly. When the meth is ~99% pure, a tenth a percent either way is angels dancing on the head of a pin. Wanna chase the fly? Chase it! Wanna get the meth out? Get it out!

I disagree. 1 degree of rotational error magnifies. From trigonometry, if your isocenter is 7 cm from the target, 1 degree of rotational error gives 1.2 mm of translation. So what is your PTV? 0-1 mm of PTV might be sufficient if you're precise enough in patient position. But if your isocenter is further away or rotation is more than 1 degree... Now you've missed part or all of the target.

I don't believe in going bigger than 1 mm PTV because then I'm just going back to GK or multi-isocentric linac treatments. IMO, what is the point of doing SRS if your margin is 2-3 mm?

If you only do 3D couch corrections with an isocenter far from some of your targets, the rotation errors can absolutely still be uncorrected and you miss part or all of your target again. If you're not using a 6-DOF couch, I think you should absolutely set a limit to how far a target can be from your isocenter. Hyperarc and many related SRS techniques will often put your isocenter well away from at least some of your targets, so you need to be aware of that.

agree with most of what you are saying- especially point 5 re fusion accuracy (i also find contrast helps with these fusions and sometimes have seen different enhancement patterns on ct and MRI including several instances where the ct enhancement was larger than that seen on mri). For insurance and logistic reasons, getting timely spatially corrected volumetric mri can be difficult, and when this is an issue, it does sway me to add margin, and when I add margin, I fractionate.

I don't treat unless I have an MRI within 14 days of treatment, preferably within 7. There is data showing worse outcomes when the MRI is older than 13 days. I have seen lesions grow several mm in two weeks, and so if your MRI is older than that you are straight up guessing about growth at that point. That's a hard no for me.

I have been using UAB approach for 4-5 years now.

When I talked to the UAB folks they have always used microMLC. My impression is that they don't understand why anyone would do these treatments without microMLCs.

Do differ on extent to which micro mlcs have impact on plan for small lesions. Scarbtj probably could comment more, but with single iso vmat 1) many of lesions seeing dose delivered by larger peripheral 5mm mlcs away from the 2.5 central micromlc? 2) collimator rotations really lessen effect of mlc size. I dont have hyperarc, but would love to get it and play around with it.

I ran a lot of plans with microMLC vs. regular MLC to justify the cost of a microMLC equipped linac. For tiny lesions there is a huge difference in metrics like conformity and gradient index. But for all lesions, you add on the order of 0.6 - 1.0 cc of V12 for every lesion treated with regular MLCs compared to microMLC, and this holds up even for large lesions. So if you treat a 15 small brain met case, now you've added ~10 cc of V12 to the entire brain. This might actually disqualify a patient from CE.7 trial which limits whole brain V12 to 30 cc. Now does this whole brain V12 actually matter when it's scattered throughout the brain? I don't know. But I don't really want to find out either.

As for your point about larger peripheral MLCs, it's the center 16 cm that gets the HDMLCs. So usually the lesions will be in there. But you have to decide whether you'll accept some being treated by the standard MLCs (UAB does, and it's a minority of lesions obviously). As for point 2, not sure what you're referring to. Maybe I'm unaware of something.

 

[evilbooyaa]

Some additional thoughts. If you want gamma knife like plans, you need to tolerate 40-50% hot spots, which is what UAB does. That could turn out to be a problem if hot spot is in ring of "normal brain" - PTV-gtv as paper from Emory recently suggested, where they related necrosis to dose>110% in this ring for fractionated treatments(disclaimer- I only read the abstract) and this could be an argument against margin. I am not sure the answer here.

Do you have that paper? We used to have this issue frequently before we changed how the staff optimized for SRS.