CTV in Lung Cancer Discussion

[deleted1180461]

Recent mednet discussion with Drew M going full Drew M…

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[Palex80]

Recent mednet discussion with Drew M going full Drew M…

Link?

 

[drowsy12]

Drew isn’t wrong

 

[Ray D. Ayshun]

So the gist is, "I don't do a CTV, I do a huge ITV. Duh."

 

[evilbooyaa]

So the gist is, "I don't do a CTV, I do a huge ITV. Duh."

Is it a huge ITV? Or is it just like a regular ITV?

 

[Ray D. Ayshun]

Is it a huge ITV? Or is it just like a regular ITV?

He seemed to talk about his ITV like it was special, as opposed to just saying "I expand my ITV directly to a PTV."

 

[OTN]

"I contour every little fluff and finger that comes out from the primary tumor and then add an ITV" isn't that remarkable.

 

[Ray D. Ayshun]

"I contour every little fluff and finger that comes out from the primary tumor and then add an ITV" isn't that remarkable.

There are ways of thoughtlessly contouring post-obstructive atelectasis that could make an ITV larger than a uniformly expanded G/ITV to ctv after thoughtful creation of the G/ITV. The verbal diarrhea gave me the impression this was an ITV+ he was talking about. Basically a whIteTV (contour the connected white ****).

 

[deleted1180461]

Sigh.

The point was the irony of making a look-@t-me-ish controversial statement of “0 mm CTV” then ripping on someone for only doing a single expansion off the GTV.

 

[Ray D. Ayshun]

Sigh.

The point was the irony of making a look-@t-me-ish controversial statement of “0 mm CTV” then ripping on someone for only doing a single expansion off the GTV.

Fair enough. It does speak to some of the abdsurdity of our field. I felt like a HN attending who trained me was trying to see how much he could violate consensus guidelines in order to presumably be able to brag about it at ASTRO or something.

 

[deleted1180461]

Fair enough. It does speak to some of the abdsurdity of our field. I felt like a HN attending who trained me was trying to see how much he could violate consensus guidelines in order to presumably be able to brag about it at ASTRO or something.

I can imagine being at a thoracic tumor board and hearing rad oncs argue about this and trying to make the same joke I did only to further stoke the argument. We must look like a total clown show.

 

[drowsy12]

The simple argument is that we don’t need CTV in the lung, which I agree with. Your mileage may vary. Not everything needs to be so deep, controversial, or past trauma inducing here.

 

[Ray D. Ayshun]

The simple argument is that we don’t need CTV in the lung, which I agree with. Your mileage may vary. Not everything needs to be so deep, controversial, or past trauma inducing here.

Particularly if you throw a 1 cm ptv margin on like the paper he cited...

 

[drowsy12]

if there was a different paper I may have missed it. the one im aware of is this:

https://www.sciencedirect.com/science/article/pii/S0167814023000439?via%3Dihub#s0005

they used 5 mm PTV straight off GTV in the 0 mm CTV arm.

 

[NotMattSpraker]

This is an interesting discussion but as always very RO-y.

I dont find any of this to be apples to apples because it is a moving target that is somewhat challenging to set up, generally speaking. PET/CT guidance for target delineation, planning techniques, use of 4DCT versus other types of motion investigation, and delivery techniques/imaging all make a huge difference. Aligning to bone versus soft tissue, etc etc.

A lot of trials do not have good RTQA. People miss.

Theres also the concept of declaring safe omission for the gen pop off a null finding in a small phase II trial. This is different than implementing something new off a positive finding. (Drew should know better!)

This is an intriguing concept where Id love to enroll someone on a trial or registry if we evaluated this question in some controlled, objective way.

But, we are Rad Onc, so.

As an aside, anyone see this? Structure-specific rigid dose accumulation dosimetric analysis of ablative stereotactic MRI-guided adaptive radiation therapy in ultracentral lung lesions - Communications Medicine

One of my biggest desires out of the adaptive folks is some dose accumulation techniques. I want to know what someone actually got. Admittedly, this is not easy to do.

But a paper came out and this is compelling in my opinion, especially for re-irradiation.

 

[Ray D. Ayshun]

Well, I'd love to be done with a ctv. If it's as Drew's paper suggested, gtv + 1 cm to ptv then there's still a ctv. Otoh, if as drowsy suggests, gtv, or hopefully itv, +5mm to ptv works, then I'm all for it. Is anyone else doing this.

 

[drowsy12]

I would argue that we all know there is never going to be a randomized trial for something like lung CTV. It would need to be massive to do a non inferiority study, and that is not practical or rational for this minor a question.

Instead ask yourself what randomized evidence we have to support using a CTV in the lung? Why does potential microscopic disease need 60 gy anyways? How many times have you had an isolated failure in the putative CTV? Our PTVs themselves are already covering theoretical adjacent microscopic disease to full dose. Why don’t we use CTVs in stage 1 SBRT?


All of that plus some data makes me comfortable starting to think about dropping it, but I totally get why others wouldn’t, I just don’t know that we will get much more large scale randomized data or evidence. Hopefully people publish their experiences for those like Drew doing it standardly.

to me it almost seems too Rad-Oncy to be so conservative with something like this.

 

[NotMattSpraker]

I would argue that we all know there is never going to be a randomized trial for something like lung CTV. It would need to be massive to do a non inferiority study, and that is not practical or rational for this minor a question.

Instead ask yourself what randomized evidence we have to support using a CTV in the lung? Why does potential microscopic disease need 60 gy anyways? How many times have you had an isolated failure in the putative CTV? Our PTVs themselves are already covering theoretical adjacent microscopic disease to full dose. Why don’t we use CTVs in stage 1 SBRT?


All of that plus some data makes me comfortable starting to think about dropping it, but I totally get why others wouldn’t, I just don’t know that we will get much more large scale randomized data or evidence. Hopefully people publish their experiences for those like Drew doing it standardly.

to me it almost seems too Rad-Oncy to be so conservative with something like this.

I disagree that it is conservative to be hesitant to shrink a target volume in a curative case. Lets have everyone use IMRT and 4DCT first, way less weird way to improve toxicity for our patients.

This would be a good use of a registry. Its a small change that is reasonable to do with little data, but it may be harmful, so you follow it out prospectively. We have tools between The Words of Drew and RCT to decide what is best haha.

Hey maybe ASTRO can set up a lung registry for this with their new found regulatory captured riches. Drew is an ASTRO guy isnt he? Hook it up!

 

[deleted1180461]

The simple argument is that we don’t need CTV in the lung, which I agree with. Your mileage may vary. Not everything needs to be so deep, controversial, or past trauma inducing here.

it’s totally fine to make the argument that you don’t need a ctv if you contour every last white bit on the lung window 4d max projection then add a single large expansion but then don’t patronize someone who essentially does for all intents and purposes the same thing. Clearly I suck at memes if I have to spell this out.

 

[Palex80]

it’s totally fine to make the argument that you don’t need a ctv if you contour every last white bit on the lung window 4d max projection then add a single large expansion but then don’t patronize someone who essentially does for all intents and purposes the same thing. Clearly I suck at memes if I have to spell this out.

What perhaps needs to be challenged is the whole ICRU-50 concept.

Many already believe that the full dose should only be delivered to the GTV with a tiny PTV margin, given all the gimmicks that we have (from CBCT, to fiducials, to MR-linac).

The CTV is also something to treat, however it likely does not require the dose that the GTV is getting.

In other words:

Treating the whole prostate with the same dose, for instance 20 x 3 Gy is likely not necessary.
It is very likely that giving something like 17 x 3 Gy to the entire prostate and SIBing the dominant intraprostatic nodule(s) with 3 x 3 Gy would deliver the same bPFS results (and likely with lower toxicity).

Perhaps we should be creating plans where we would simply be irradiating the GTV (with a tiny PTV margin), contour the CTV (but not prescribe dose to it) and simply look at how much of the dose prescribed to the GTV "spills over" to the areas of the CTV that are outside of the GTV. If that metric is "good" (and we would have to establish these metrics for each disease and scenario), then the plan is fine.

So, if I am treating 30 x 2 Gy to the GTV of a stage III NSCLC and my CTV (outside of the GTV) still receives at least 80% of the 60 Gy to 95% of the volume, then the plan is ok. Because 95% of the volume that I assessed as at risk for microscopic disease is still getting at least 48 Gy. And 48 Gy are fine for sublclinical disease.

 

[deleted1180461]

This is exactly what I do for NSCLC. 33 fractions. GTV + PTV gets 6600. CTV + PTV gets 5940. If you don’t believe in dose escalation beyond 60 you would do 60 and 54.

 

[CurbYourExpectations]

 

[taserlaser]

This is a totally reasonable concept I think we should push more. I do see some papers out of Australia for skin that are treated to two dose levels with VMAT, GTV gets the therapeutic dose and the margin gets the microscopic dose. Can’t remember what margins they used. Electrons were quite good for this and as finicky as they were. Treating a huge swath of skin to the full dose is not fun and probably excessively toxic. Caveat being I do see recurrences right below that threshold and not all squams perhaps are as radiosensitive as others.

There is a lot we can do to fine tune what we do that have nothing to do with MR linac or protons