Hippocampal avoidance

[Neuronix]

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

Dosimetric Factors Related to Radiation Necrosis After 5-Fraction Radiosurgery for Patients With Resected Brain Metastases - PubMed

To our knowledge, this is the first study that investigated dosimetric factors that predict for RN after 5-fraction hypofractionated SRS for rBM. Hotspot location and magnitude appear important for predicting RN risk, thus these parameters should be carefully considered during treatment planning.

www.ncbi.nlm.nih.gov

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[Tigerstang]

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.

Do you know how I know you work in an academic setting?

 

[Neuronix]

Do you know how I know you work in an academic setting?

Is it because I cite data or because I insist on doing risky procedures in the best way possible?

Both should be applicable to ALL radiation oncologists, regardless of setting.



PS: Or maybe you're pulling my leg and it's the little "Faculty" and "PhD" tags next to my posts

 

[nkmiami]

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.



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.



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.



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.

went for a site visit to UAB a number of years ago and thought they were using a trilogy (at the time) but not sure about that. Obviously, today they are a showcase site for varian and have all the bells and whistles. Had discussions with them about 6 years ago about mlcs, and their thinking may have changed. In terms of mri, having an mri sim in your department may be so important in this setting- it can be really hard to get timely and repeat mris with crappy insurance.

(in post op setting, but necrosis related to dose in the ptv margin)- this is something I totally used to ignore, but now not so much?

Dosimetric Factors Related to Radiation Necrosis After 5-Fraction Radiosurgery for Patients With Resected Brain Metastases - PubMed

To our knowledge, this is the first study that investigated dosimetric factors that predict for RN after 5-fraction hypofractionated SRS for rBM. Hotspot location and magnitude appear important for predicting RN risk, thus these parameters should be carefully considered during treatment planning.

pubmed.ncbi.nlm.nih.gov

 

[Tigerstang]

Is it because I cite data or because I insist on doing risky procedures in the best way possible?

Both should be applicable to ALL radiation oncologists, regardless of setting.



PS: Or maybe you're pulling my leg and it's the little "Faculty" and "PhD" tags next to my posts

Before you lecture us on the best way to do things, spend some time in a community cancer center without all the resources available in the Ivory tower. Your perspective will change, I guarantee it.

 

[nkmiami]

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.

hyperarc and changing iso/ssd seems like it would influence how much peripheral target "sees" micromlcs . Are your numbers for hyperarc?

 

[scarbrtj]

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.



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.



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.



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.

eh well. Worst case what you're talking about is this (coordinate scales in mm's below) assuming a 0.5cm diameter (a pretty small met, calcs will be better/propitious-er for bigger met) lesion which has a volume of ~0.065cc's:

They overlap by ~0.046cc's (pi/12*[1+4*2.5]*[-1+2*2.5]^2), ~70% volume overlap... and just picture the dose(s) isovolume(s) overlaps. So even then you don't miss "all." If you add ~1mm margins and have 7cm target-to-iso distance and a 1 degree single axis rotation error we have this:

With about 99% volume overlap.

I like a teeny margin. Especially if the patient coughs, or silently valsalvas or farts, or my hand trembled when drawing the GTV, or something

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.

What if one day the computer decided to keep two 2.5mm leaves together as they travelled such that the overall dose distribution in a region "devolved" into that of a treatment given by a 0.5cm leaf linac? The horror.

 

[Neuronix]

hyperarc and changing iso/ssd seems like it would influence how much peripheral target "sees" micromlcs . Are your numbers for hyperarc?

Yes. The analysis does assume every target gets the microMLC, which is true in most cases (remember, microMLC is 8 cm from isocenter).

eh well. Worst case what you're talking about is this (coordinate scales in mm's below) assuming a 0.5cm diameter (a pretty small met, calcs will be better for bigger met) lesion which has a volume of ~0.065cc's:

With about 99% volume overlap.

I like a teeny margin. Especially if the patient coughs, or silently valsalvas or farts, or my hand trembled when drawing the GTV, or something

Exactly what the numbers look like depend on your assumptions. You're right that if you add 1 mm PTV and you're off by 1.2 mm... Well you aren't really missing. At least if you're aware of the issue and are accounting for it, that's fine. I bring it up to state that people need to be aware of the issue.

Before you lecture us on the best way to do things, spend some time in a community cancer center without all the resources available in the Ivory tower. Your perspective will change, I guarantee it.

I'm not engaging you further on this. This is a technical discussion, and all you have added to the discussion is to go after me personally. This is a professional forum for professional, not personal, discussions.

 

[nkmiami]

Yes. The analysis does assume every target gets the microMLC, which is true in most cases (remember, microMLC is 8 cm from isocenter).



Exactly what the numbers look like depend on your assumptions. You're right that if you add 1 mm PTV and you're off by 1.2 mm... Well you aren't really missing. At least if you're aware of the issue and are accounting for it, that's fine. I bring it up to state that people need to be aware of the issue.



I'm not engaging you further on this. This is a technical discussion, and all you have added to the discussion is to go after me personally. This is a professional forum for professional, not personal, discussions.

just to clarify, nothing i said applies to hyperarc and I dont know much about it. If I treat many mets with single isocenter, my philosophy is to add a bit of margin and fractionate. Assuming alpha/beta 2, V12 is equivalent V6.5 x 3, which is a lot more foregiving.... Did an analysis for my center a number of years ago where I looked at v12 vs V12 fractionated equivalent with 1 mm margin on gtv and found fractionation to be quite foregiving even with a bit of margin. ..

If you are treating 20 mets at 21 gy in one shot, then yes, it seems you need to worry about a lot

 

[evilbooyaa]

Before you lecture us on the best way to do things, spend some time in a community cancer center without all the resources available in the Ivory tower. Your perspective will change, I guarantee it.

How about if you don't have the equipment or ability to coordinate care to do it properly then maybe you shouldn't be doing it?

Maybe your community cancer center should work on getting an MRI that can be scheduled in decent time to get a tx planning MRI done. Doesn't have to be in the department.

Or, ya know, just accept that you apparently don't have the equipment to do SRS as ideally and either 1) don't do it or 2) increase margins or 3) come up with other ways, like IV contrast at time of sim as has been previously mentioned.

Same thing with Brachy and SBRT. If you can't do it properly (like doing spine SBRT without CBCT is what I've seen people try) then just refer to the place that does it properly.

 

[KHE88]

How about if you don't have the equipment or ability to coordinate care to do it properly then maybe you shouldn't be doing it?

Maybe your community cancer center should work on getting an MRI that can be scheduled in decent time to get a tx planning MRI done. Doesn't have to be in the department.

Or, ya know, just accept that you apparently don't have the equipment to do SRS as ideally and either 1) don't do it or 2) increase margins or 3) come up with other ways, like IV contrast at time of sim as has been previously mentioned.

Same thing with Brachy and SBRT. If you can't do it properly (like doing spine SBRT without CBCT is what I've seen people try) then just refer to the place that does it properly.

Rural rad onc here with limited PET, MRI, and biryani options available in the boonies. Chiming in.

I get where Tigerstang is coming from. Most (>90%?) rad oncs have never practiced in a truly rural environment, so it's understable there's a disconnect.

Forgoing care is just often not an option. The patient will refuse to travel, and you just have to accept the risk of higher toxicity. I always give a meaningful dose. This requires being creative sometimes.

I've seen it both ways. I have seen massive tumor regrowth in < 14 days on MRI. I have also seen patients tossed around for months trying to travel and get a bunch of specialized scans and they come back and have additional disease by that time. It's a balancing act on a case-by-case basis trying to determine what's reasonable to delay start of treatment to get and what's not.

Giving whole brain or sending to hospice because you can't do SRS exactly, 100% right and the patient won't travel is totally unacceptable in my opinion.

 

[RickyScott]

How about if you don't have the equipment or ability to coordinate care to do it properly then maybe you shouldn't be doing it?

Maybe your community cancer center should work on getting an MRI that can be scheduled in decent time to get a tx planning MRI done. Doesn't have to be in the department.

Or, ya know, just accept that you apparently don't have the equipment to do SRS as ideally and either 1) don't do it or 2) increase margins or 3) come up with other ways, like IV contrast at time of sim as has been previously mentioned.

Same thing with Brachy and SBRT. If you can't do it properly (like doing spine SBRT without CBCT is what I've seen people try) then just refer to the place that does it properly.

It wasnt that long ago that I was doing fractionated srt at major research center with good results on trilogy and no six degree couch because that was what state of the art then.
We thought were hot sh because using vmat. We
Are talking like 7 years ago. Good fusion capability and some type of rotational solution will get you really close to neuronix.

Neuronix cited UCSF mri timeliness data for radiosurgery. Nice article, but you can also take from that article that even program that has long history of excellent stereo can have timeliness issues obtaining mris.

I wouldn’t do whole brain because insurance co/ hospital wouldn’t let me do mprage mri for stereo planning and had to use an older thicker sliced mri for solitary met. Would add margin and fractionate. Also Any tumor that explodes in 7 days has really bad biology and you should really use contrast under these circumstances.

 

[taserlaser]

It wasnt that long ago that I was doing fractionated srt at major research center with good results on trilogy and no six degree couch because that was what state of the art then.
We thought were hot sh because using vmat. We
Are talking like 7 years ago. Good fusion capability and some type of rotational solution will get you really close to neuronix.

And when the cyberknife inevitably breaks down at large institution you have to convert the plans to VMAT anyway while you wait for a head change and recommissioning since the beam profile changed... or so I’m told >_>

 

[RickyScott]

And when the cyberknife inevitably breaks down at large institution you have to convert the plans to VMAT anyway while you wait for a head change and recommissioning since the beam profile changed... or so I’m told >_>

I am really biased but aside from marketing, cybernife seems like such a huge waist in the brain, actually inferior product to any varian linac with cone beam and eclipse, or any old linac with brain lab add on.

 

[Tigerstang]

Rural rad onc here with limited PET, MRI, and biryani options available in the boonies. Chiming in.

I get where Tigerstang is coming from. Most (>90%?) rad oncs have never practiced in a truly rural environment, so it's understable there's a disconnect.

Forgoing care is just often not an option. The patient will refuse to travel, and you just have to accept the risk of higher toxicity. I always give a meaningful dose. This requires being creative sometimes.

I've seen it both ways. I have seen massive tumor regrowth in < 14 days on MRI. I have also seen patients tossed around for months trying to travel and get a bunch of specialized scans and they come back and have additional disease by that time. It's a balancing act on a case-by-case basis trying to determine what's reasonable to delay start of treatment to get and what's not.

Giving whole brain or sending to hospice because you can't do SRS exactly, 100% right and the patient won't travel is totally unacceptable in my opinion.

bingo.

sorry to have offended you professor, but real life is a lot more complicated than life at the university. it's painful, but it's true.

 

[PhotonBomb]

bingo.

sorry to have offended you professor, but real life is a lot more complicated than life at the university. it's painful, but it's true.

Yeah you’re a real hero maaaaaaaan

 

[deleted1002574]

Telling ya man, they really do look down on the rest of us from the tower.. it's really interesting. Then you spend some time up in the tower and realize that their **** stinks, too, but they have better ventilation and also are habituated to the stench.

 

[evilbooyaa]

Giving whole brain or sending to hospice because you can't do SRS exactly, 100% right and the patient won't travel is totally unacceptable in my opinion.

bingo.

sorry to have offended you professor, but real life is a lot more complicated than life at the university. it's painful, but it's true.

If you want to put 2mm Margin on b/c your MRI is 21-28 days old, very reasonable IMO. Just have a strategy. Don't do things the same way the academics do (0 or 1mm margin) if you're not doing the work-up, imaging, time from MRI to tx, etc. the same way. If you want to do IV contrast at time of sim to allow for better fusion to your MRI, then OK.

Don't try to be slick and end up underdosing the tumor because you want to copy some, but not all, of what academic folks (the ones who write the papers that you then use to make treatment decisions) do.

Respect your ability or inability to replicate a process, and if you are unable to replicate a process, make adjustments so you don't end up hurting the patient.

 

[Lamount]

Telling ya man, they really do look down on the rest of us from the tower.. it's really interesting. Then you spend some time up in the tower and realize that their **** stinks, too, but they have better ventilation and also are habituated to the stench.

Ventilation is important... and so is having reliable imaging for target delineation when performing stereotactic treatments.

 

[deleted1002574]

True, for optimal SRS .. Reliable imaging > biryani > ventilation

 

[Pointless]

If you want to put 2mm Margin on b/c your MRI is 21-28 days old, very reasonable IMO. Just have a strategy. Don't do things the same way the academics do (0 or 1mm margin) if you're not doing the work-up, imaging, time from MRI to tx, etc. the same way. If you want to do IV contrast at time of sim to allow for better fusion to your MRI, then OK.

Don't try to be slick and end up underdosing the tumor because you want to copy some, but not all, of what academic folks (the ones who write the papers that you then use to make treatment decisions) do.

Respect your ability or inability to replicate a process, and if you are unable to replicate a process, make adjustments so you don't end up hurting the patient.

So, I have a question for all the people advocating for 0 margin. How is it conceivable to you that there is literally zero margin for error in the delivery of your treatment? Does not the MRI spatial distortion alone account for about 1 mm (not to mention fusion error allowance)? And then patient setup, whether frameless or frame, you honestly believe that it is reproducible to 0 mm?

There have been studies done on this that have concluded, very reasonably IMO, that 2 mm should be the standard approach. How is it that in the hallowed halls of an academic institution, all of the accepted laws of physics no longer apply?

 

[evilbooyaa]

So, I have a question for all the people advocating for 0 margin. How is it conceivable to you that there is literally zero margin for error in the delivery of your treatment? Does not the MRI spatial distortion alone account for about 1 mm (not to mention fusion error allowance)? And then patient setup, whether frameless or frame, you honestly believe that it is reproducible to 0 mm?

There have been studies done on this that have concluded, very reasonably IMO, that 2 mm should be the standard approach. How is it that in the hallowed halls of an academic institution, all of the accepted laws of physics no longer apply?

Idk. I do 1. Don't think I'll ever go to 0mm on a frameless set-up.

 

[deleted1002574]

Are you saying that decades of GammaKnife data from multiple institutions that included tens of thousands of patients are potentially falsified or that they somehow broke the laws of physics? I mean, studies are studies, man. But 0mm is standard of care and the outcomes are excellent. Odd comment.

So, I have a question for all the people advocating for 0 margin. How is it conceivable to you that there is literally zero margin for error in the delivery of your treatment? Does not the MRI spatial distortion alone account for about 1 mm (not to mention fusion error allowance)? And then patient setup, whether frameless or frame, you honestly believe that it is reproducible to 0 mm?

There have been studies done on this that have concluded, very reasonably IMO, that 2 mm should be the standard approach. How is it that in the hallowed halls of an academic institution, all of the accepted laws of physics no longer apply?

 

[Pointless]

Are you saying that decades of GammaKnife data from multiple institutions that included tens of thousands of patients are potentially falsified or that they somehow broke the laws of physics? I mean, studies are studies, man. But 0mm is standard of care and the outcomes are excellent. Odd comment.

Sorry, thought it was clear that I was talking linac-based. Wasn't that what we were talking about?

 

[medgator]

Gk lends itself to 0 mm, with it being MR planning based with a frame. Not sure much else does...

 

[deleted1002574]

Oh, when you said frame or frameless, I figured you were talking about GK, too, my bad,

 

[Pointless]

Oh, when you said frame or frameless, I figured you were talking about GK, too, my bad,

Not the first time, and certainly won't be the last, that I failed to appropriately communicate thoughts lol.

 

[PhotonBomb]

You shouldn’t be doing radiosurgery or conventional frac in private practice

 

[radiation]

One thing that gets lost in the margin discussion is that the appropriate dose for radiosurgery still has not been established and is surprisingly widely variable from center to center. RTOG 90-05 doses are the most commonly quoted, but that study is almost 30 years old and a third of the pts had previously radiated gliomas. 40% of the linac pts also had a conformity index of >2 (!) and necrosis was probably underreported because MRI not required...but I digress.

The large randomized SRS studies (ie Brown JAMA 2016) didn't use "standard" RTOG doses (used 20 gy for 2-3 cm mets vs 18 gy in RTOG 9005). On the other hand, many centers like Yale have dropped their "top end" dose to 22 gy max because of necrosis concerns and other places will top out at 20 gy for tiny lesions. Biologically it makes no sense to dose escalate subcentimeter mets and de-escalate larger ones (we only do because of normal tissue tolerance).

theMednet

www.themednet.org

Varying use of margins, isodose line, and prescription doses can be mixed and matched and give the same thing. I'm just spitballing here, but using an 1-2 mm margin and prescribing 18 gy to the 50% isodose line is not going to be that much different than using zero margin and prescribing 20 gy to the 90% isodose.

So a lot of this margin talk is really just semantics if we are not controlling for isodose line, margin, and dose.

 

[Newquagmire]

What labs are people checking for memantine?

 

[Palex80]

Idk. I do 1. Don't think I'll ever go to 0mm on a frameless set-up.

We even do 2mm: 1mm CTV + 1mm PTV.

 

[Tigerstang]

If you want to put 2mm Margin on b/c your MRI is 21-28 days old, very reasonable IMO. Just have a strategy. Don't do things the same way the academics do (0 or 1mm margin) if you're not doing the work-up, imaging, time from MRI to tx, etc. the same way. If you want to do IV contrast at time of sim to allow for better fusion to your MRI, then OK.

Don't try to be slick and end up underdosing the tumor because you want to copy some, but not all, of what academic folks (the ones who write the papers that you then use to make treatment decisions) do.

Respect your ability or inability to replicate a process, and if you are unable to replicate a process, make adjustments so you don't end up hurting the patient.

again, thanks professor. I'm sure the fact that I'm in the community completely negates that I trained at a top tier residency, published a crap ton, and know how to practice radonc, because you treat 12 people a day and have time to write papers while I'm out treating 45 people a day. get over yourself.

 

[scarbrtj]

Telling ya man, they really do look down on the rest of us from the tower.. it's really interesting. Then you spend some time up in the tower and realize that their **** stinks, too, but they have better ventilation and also are habituated to the stench.

Only need ventilation when doing "SRS" for lung, not brain.
"High frequency percussive ventilation for respiratory immobilization in radiotherapy"

So, I have a question for all the people advocating for 0 margin. How is it conceivable to you that there is literally zero margin for error in the delivery of your treatment? Does not the MRI spatial distortion alone account for about 1 mm (not to mention fusion error allowance)? And then patient setup, whether frameless or frame, you honestly believe that it is reproducible to 0 mm?

There have been studies done on this that have concluded, very reasonably IMO, that 2 mm should be the standard approach. How is it that in the hallowed halls of an academic institution, all of the accepted laws of physics no longer apply?

Physics comes into play with dose fall off too. A bit more dose at isocenter, versus less, means more dose fall off past the GTV target edge. So it's two things you have to look at (three really): dose (conformality) and (PTV) margin. Can't just say 0mm margins violate "laws of physics." Although I don't like them, because I don't like to have to go hot to negate them. Thousand gray isocenter dose would allow for negative 2 cm margins e.g.

 

[RickyScott]

Btw You cam contact manufacturer of mri for stereo sequences that minimize spatial distortion. We use them. The barrier is often getting approval 2nd mri that is now stat!

 

[evilbooyaa]

again, thanks professor. I'm sure the fact that I'm in the community completely negates that I trained at a top tier residency, published a crap ton, and know how to practice radonc, because you treat 12 people a day and have time to write papers while I'm out treating 45 people a day. get over yourself.

Not sure why you're so salty about this like everything is a personal attack on you. It's not a knock on you, personally, as a person or a radiation oncologist. Just be smart, don't have hubris, and make adjustments as necessary. If you don't have easy access to MRI, make adjustments.

Not sure if I'm just getting trolled at this point - I'm not saying don't do SRS at all, but if you need to increase margins and/or fractionate more because you can't do 0/1mm margin safely (meaning in terms of oncologic control) so that you can do it safely (in terms of toxicity outcomes) in a patient that can't/won't travel, then OK.

If you stubbornly do 0/1mm margin on an MRI that is 28 days old you are potentially putting the patient at higher risk of recurrence. Feel free to use that information as you will. Granted the cut-off of 14 days seems arbitrarily selected and it's probably on a spectrum.

Yeesh.

 

[Neuronix]

So, I have a question for all the people advocating for 0 margin. How is it conceivable to you that there is literally zero margin for error in the delivery of your treatment? Does not the MRI spatial distortion alone account for about 1 mm (not to mention fusion error allowance)? And then patient setup, whether frameless or frame, you honestly believe that it is reproducible to 0 mm?

UAB treats everyone with zero margin, including single isocenter with mets several cm away. I, as have many others, have asked them the question on 0 margin, and the response is just that their failure rate is low so it's fine. I get this a lot--we do it this way and it works fine so it's fine. Heck, maybe dose fall off does take care of small margins. Maybe it depends on dose (20 Gy for small mets or 24 Gy for example)? Maybe it depends on technique? Maybe in the end it's not even all that important (I don't really think so but I could be wrong)?

There was a Hyperarc panel at the last ASTRO and the PTV margins used among the panelists were all over the place. I've also surveyed rad oncs nationally on their linac SRS PTVs and gotten responses almost equally distributed from 0 - 3 mm. So... Everyone thinks on this differently.

MRI spatial distortion still applies to GK as well.

There have been end to end tests of frameless and frame and with a good setup the error ends up being on the order of 0.5 (frame) - 1 mm (frameless). So you end up with the argument that the dose fall off handles the disease if you use zero margin.

There have been studies done on this that have concluded, very reasonably IMO, that 2 mm should be the standard approach. How is it that in the hallowed halls of an academic institution, all of the accepted laws of physics no longer apply?

I still do 1 mm PTV on linac personally. Another issue is that this is a moving target. The linacs and setups for SRS keep having incremental benefits that can reasonably get you down to 1 mm if you're careful. So it's not too much of a leap IMO to go down to 0 mm. Our physics group and I discuss this regularly, and again we have people on all sides of this argument from 0 to 2 mm.

What labs are people checking for memantine?

There are case reports of liver failure, and also need dose adjustments for renal failure. Since our patients are typically on systemic therapy, I just take a peek at their labs ordered by med onc.

Neuronix cited UCSF mri timeliness data for radiosurgery. Nice article, but you can also take from that article that even program that has long history of excellent stereo can have timeliness issues obtaining mris.

I wonder if they still allow 14+ days from MRI to treatment given their analysis?


REMINDER: Personal attacks on SDN members will not be tolerated. Some posts have been removed.

 

[RickyScott]

Btw You cam contact manufacturer of mri for stereo sequences that minimize spatial distortion. We use them. The barrier is often getting approval 2nd mri that is now stat!

I have always been curious- effect of target miss in terms of cancer control? Old thinking was that if every cell is capable of regrowing a tumor and you are spatially off such that an area of tumor is underdosed by 20%, you almost certainly would fail. I am not so sure of that anymore, because immune system plays such a big role now... (I am convinced that substantial errors were made historically in many excellent centers 15 years ago because looking back fusion was not great at all, but rates of local control for small lesions treated without margin are very high?)

 

[scarbrtj]

I have always been curious- effect of target miss in terms of cancer control? Old thinking was that if every cell is capable of regrowing a tumor and you are spatially off such that an area of tumor is underdosed by 20%, you almost certainly would fail. I am not so sure of that anymore, because immune system plays such a big role now... (I am convinced that substantial errors were made historically in many excellent centers 15 years ago because looking back fusion was not great at all, but rates of local control for small lesions treated without margin are very high?)

In all seriousness, the "intratumoral abscopal effect," aka the bystander effect. While the tumor-within-the-field approach works for sure, the field-within-the-tumor approach may cover mistargeting sins. Not sure that we learn/teach about that in residency!

 

[RickyScott]

In all seriousness, the "intratumoral abscopal effect," aka the bystander effect. While the tumor-within-the-field approach works for sure, the field-within-the-tumor approach may cover mistargeting sins. Not sure that we learn/teach about that in residency!

Several cases

UAB treats everyone with zero margin, including single isocenter with mets several cm away. I, as have many others, have asked them the question on 0 margin, and the response is just that their failure rate is low so it's fine. I get this a lot--we do it this way and it works fine so it's fine. Heck, maybe dose fall off does take care of small margins. Maybe it depends on dose (20 Gy for small mets or 24 Gy for example)? Maybe it depends on technique? Maybe in the end it's not even all that important (I don't really think so but I could be wrong)?

There was a Hyperarc panel at the last ASTRO and the PTV margins used among the panelists were all over the place. I've also surveyed rad oncs nationally on their linac SRS PTVs and gotten responses almost equally distributed from 0 - 3 mm. So... Everyone thinks on this differently.

MRI spatial distortion still applies to GK as well.

There have been end to end tests of frameless and frame and with a good setup the error ends up being on the order of 0.5 (frame) - 1 mm (frameless). So you end up with the argument that the dose fall off handles the disease if you use zero margin.



I still do 1 mm PTV on linac personally. Another issue is that this is a moving target. The linacs and setups for SRS keep having incremental benefits that can reasonably get you down to 1 mm if you're careful. So it's not too much of a leap IMO to go down to 0 mm. Our physics group and I discuss this regularly, and again we have people on all sides of this argument from 0 to 2 mm.



There are case reports of liver failure, and also need dose adjustments for renal failure. Since our patients are typically on systemic therapy, I just take a peek at their labs ordered by med onc.



I wonder if they still allow 14+ days from MRI to treatment given their analysis?

I am sure UAB has an MRI sim that they can use all day long and dont care if they get auth for MRI etc.

 

[evilbooyaa]

In all seriousness, the "intratumoral abscopal effect," aka the bystander effect. While the tumor-within-the-field approach works for sure, the field-within-the-tumor approach may cover mistargeting sins. Not sure that we learn/teach about that in residency!

Not to get too far off topic, but this is the concept behind GRID radiation for reirradiation of big lesions.