Planning guides for IMRT hippocampal sparing IMRT

[Tigerstang]

Does anyone have some good dosimetry guidelines for hippocampal sparing IMRT WBRT? We are trying to adopt this in our practice given the recent Ph III data and my dosimetrists are having to use 9 Arc plans to meet constraints. As much as I want to adopt this, 9 arcs for whole brains is not feasible for my throughput. Would appreciate input from those who have been able to get this accomplished with less arcs. Thank you

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[scarbrtj]

Does anyone have some good dosimetry guidelines for hippocampal sparing IMRT WBRT? We are trying to adopt this in our practice given the recent Ph III data and my dosimetrists are having to use 9 Arc plans to meet constraints. As much as I want to adopt this, 9 arcs for whole brains is not feasible for my throughput. Would appreciate input from those who have been able to get this accomplished with less arcs. Thank you

I too went down the arc rabbit hole. Right now I’m settled into nine static fields, all non coplanar. A Statue of Liberty (see: her crown) beam arrangement. None of these beams shine through the eyes. Not a quick treatment but faster than many many arcs I think. And I like the coverages and avoidances overall better. And it calculates WAYYYY faster.
Edit: will also add the arc algorithms I use seem to stumble a bit in the unique situation, unique especially with hippocamp sparing, of generating a cold region surrounded in all three dimensions by warm/hot

 

[PhotonBomb]

We use three arcs, one is a Mohawk arc

 

[PhotonBomb]

One paper I just found

Dosimetric Comparison of Four Volumetric-Modulated Arc Therapy Beam Arrangements Utilized for Hippocampal-Sparing Whole-Brain Radiation Therapy - PubMed

Overall, beam setup 3 was considered to be the best. It is worth mentioning that, apart from our results, the election of one of these beam arrangements might be dependent on the amount of patient workload at a specific institution.

pubmed.ncbi.nlm.nih.gov

 

[BobbyHeenan]

We use three arcs, one is a Mohawk arc

This is what I've done. I enrolled on NRG CC003 and passed QA with this arrangement. If I'm remembering correctly, I enrolled two patients - one whole brain and another hippocampal sparing and did two axial arcs and one mohawk.

Can't remember how we did hte cost function, etc. Physics and dosimetry were really on top of it and did well. I'm a good brain met SRS planner, but they took the ball for hippocampal sparing WBRT.

 

[evilbooyaa]

9 arcs? That's insane. 9 fields for a step n shoot plan, sure, but 9 arcs, my goodness.

2 full arcs and one non-coplanar half arc from vertex are plenty. Make sure they're using planning PTVs and that they're not trying to push the plan too homogenous - there is more heterogeneity. Even 2 arcs alone with proper collimator rotation should be able to get you to meet constraints.

Are you doing scalp sparing or something? Only other caveat of HS-WBRTis I have seen a patient with bad dry mouth from it so I routinely draw and constrain parotids now.

 

[Palex80]

4 arcs used in this plan for PCI in LD-SCLC.

Couch rotations 30°, 90°, 330° for 3 out of 4 arcs.

 

[FrostyHammer]

Honestly if I wanted to do HA-WBRT I'd just do SRS as my way of sparing the hippocampus...

 

[scarbrtj]

4 arcs used in this plan for PCI in LD-SCLC.
View attachment 303368

Couch rotations 30°, 90°, 330° for 3 out of 4 arcs.

Questions/comments from back of room:
Wish the lenses were getting less dose...
That headrest is mostly air (if cushion, if plastic it's all air) and isn't seeing as much dose as the TPS is thinking it's seeing because the TPS sees it contoured as body, but yet it must be taking the headrest (and table too it seems) into account in the calc, should we fix that

 

[PhotonBomb]

Honestly if I wanted to do HA-WBRT I'd just do SRS as my way of sparing the hippocampus...

You realize that people aren’t doing HA WBRT for patients that they think are SRS candidates. There’s a difference e

 

[Tigerstang]

Thanks to those of you who provided references. Much obliged.

 

[scarbrtj]

I'm doing this rough and dirty remotely. A H&N patient, don't have an MRI, so just put in "spheres" as hippocamp surrogates because too lazy to tease them out right now. So this is just a planning study/example. Put 0.5cm around those (spheres-marg). Subtract from normal brain (brain-minus). Lens-L is actually both lenses. Contoured in lenses, and parotids, but note I did not have to place any constraints on them due to beam placement. Arcs don't present/aim all optimal vectors on things (ie eyes, throat, lenses, parotids) we mean to miss; they never do but this is real evident in WBRT. This beam arrangement would show the optimal vectors if we could move couch and gantry at same time for an arc. Of course can't do that, so therefore here we are with static beams. Meant to put on 9 beams but lost count and put on 10.

A 9 field approach with beams like this:

optimized like this:

Paying attention to constraints like this:

And get dose distributions/DVH like this:

This was all planned and calc'd in ~30 min. Parotids maxing at ~15 Gy and lenses at ~10 Gy with zero effort. Only about 1/3 normal brain above 110% dose. The beams are about 300 MUs per beam which will take ~30 seconds per beam to deliver at 600 MU/min dose rate; at 10 beams, we're talking ~300 second total beam on time. Of course must kick couch and rotate gantry between beams so tx time will be much longer but very doable. There is no way (I think) to get eye sparing (or parotid sparing?) like this with arcs IMHO. And I can get the seahorse lower than commonly shown/reported. YMMV.

 

[Neuronix]

Yeah 3-4 arcs here, usually 1-2 non-coplanar. It always takes the dosimetrists some time to figure this out when they first start doing it.

I give this paper to the dosimetrists for one well described technique: An efficient Volumetric Arc Therapy treatment planning approach for hippocampal-avoidance whole-brain radiation therapy (HA-WBRT). - PubMed - NCBI

 

[FrostyHammer]

You realize that people aren’t doing HA WBRT for patients that they think are SRS candidates. There’s a difference e

Well, since you asked, what is an SRS candidate? Definition varies highly depending on who you talk to...

 

[scarbrtj]

Well, since you asked, what is an SRS candidate? Definition varies highly depending on who you talk to...

Who is a HA-WBRT candidate? In theory every whole brain RT candidate?

Does hippocampal avoidance even work? Is it fake news???

 

[medgator]

Well, since you asked, what is an SRS candidate? Definition varies highly depending on who you talk to...

Not sure what definition the anti WB/pro srs crowd embraces these days.. <50 lesions?

 

[PhotonBomb]

Well, since you asked, what is an SRS candidate? Definition varies highly depending on who you talk to...

For any individual provider, if they are considering WBRT, It is because for histology or disease burden or PS related reasons they have decided against SRS. In that scenario, they an then decide the utility of HA.

However, your statement that if you wanted to spare the hippocampus you would do SRS is not really a helpful one, because I’m pretty sure the person who is deciding for HA WBRT already understands the concept of SRS.

 

[taserlaser]

Best hippocampal sparing technique - decadron and hospice. I kid, I kid...

 

[Neuronix]

Best hippocampal sparing technique - decadron and hospice. I kid, I kid...

All HVLT-R scores go to zero eventually.

 

[Tigerstang]

I'm doing this rough and dirty remotely. A H&N patient, don't have an MRI, so just put in "spheres" as hippocamp surrogates because too lazy to tease them out right now. So this is just a planning study/example. Put 0.5cm around those (spheres-marg). Subtract from normal brain (brain-minus). Lens-L is actually both lenses. Contoured in lenses, and parotids, but note I did not have to place any constraints on them due to beam placement. Arcs don't present/aim all optimal vectors on things (ie eyes, throat, lenses, parotids) we mean to miss; they never do but this is real evident in WBRT. This beam arrangement would show the optimal vectors if we could move couch and gantry at same time for an arc. Of course can't do that, so therefore here we are with static beams. Meant to put on 9 beams but lost count and put on 10.

A 9 field approach with beams like this:

optimized like this:

Paying attention to constraints like this:

And get dose distributions/DVH like this:

This was all planned and calc'd in ~30 min. Parotids maxing at ~15 Gy and lenses at ~10 Gy with zero effort. Only about 1/3 normal brain above 110% dose. The beams are about 300 MUs per beam which will take ~30 seconds per beam to deliver at 600 MU/min dose rate; at 10 beams, we're talking ~300 second total beam on time. Of course must kick couch and rotate gantry between beams so tx time will be much longer but very doable. There is no way (I think) to get eye sparing (or parotid sparing?) like this with arcs IMHO. And I can get the seahorse lower than commonly shown/reported. YMMV.

This is great but if every whole brain plan I produced had 9 beams my RTTs would beat me up in the parking lot.

 

[scarbrtj]

This is great but if every whole brain plan I produced had 9 beams my RTTs would beat me up in the parking lot.

Have they been drawing and quartering you for 9 arcs?! We allow full couch kicking from control panel outside room so it ain't so bad.

 

[Palex80]

Questions/comments from back of room:
Wish the lenses were getting less dose...
That headrest is mostly air (if cushion, if plastic it's all air) and isn't seeing as much dose as the TPS is thinking it's seeing because the TPS sees it contoured as body, but yet it must be taking the headrest (and table too it seems) into account in the calc, should we fix that

Thank you.

Indeed, less dose to the lenses would have been nice. However this was a case with very tight constraints at the hippocampi, which had to be met on trial. So, indeed, we had to push for less dose to the hippocampi and "sacrifice" the lenses.

Our dosimetrists contour everything. Couch, any positioning aid, etc. And yes, table and positioning aids do absorbe dose...they are not made of air. Physics have looked into that and run everything through the CT and assigned values to them. I am aware that some clinics/people do not take these into account. We do.

 

[FrostyHammer]

In theory every whole brain RT candidate?

Bingo!

Not sure what definition the anti WB/pro srs crowd embraces these days.. <50 lesions?

That's my point... It all depends on who you talk to. Go to Flickinger and Lunsford and they might just agree with the 50 cutoff!

For any individual provider, if they are considering WBRT, It is because for histology or disease burden or PS related reasons they have decided against SRS. In that scenario, they an then decide the utility of HA.

However, your statement that if you wanted to spare the hippocampus you would do SRS is not really a helpful one, because I’m pretty sure the person who is deciding for HA WBRT already understands the concept of SRS.

Well, not necessarily. My point above was that indications for SRS are highly heterogeneous and clinician dependent. Yes, there's clear data for 1-4 lesions etc, but outside of that. What I'm saying is that those with a higher lesion count threshold for applying SRS would be more likely to use SRS as a means for hippocampal sparing, versus vice versa. Scarbrtj's statement above is on point. It's theoretically every WBRT candidate, but all depends on the clinical judgment of the treating clinician RE: the "indication" for SRS.

Remember: this is all an art, not a science.

 

[Tigerstang]

Have they been drawing and quartering you for 9 arcs?! We allow full couch kicking from control panel outside room so it ain't so bad.

I never do 9 arcs. I am in private practice, 50 patients plus per linac per day. Never gonna happen.

 

[Palex80]

I never do 9 arcs. I am in private practice, 50 patients plus per linac per day. Never gonna happen.