Breast RNI and IMN coverage Discussion.... Again. Breast is the worst x 4?

[drowsy12]

---

Members don't see this ad.

im not a minimum dose guy

 

[Ray D. Ayshun]

Debating sparing a breast implant is the most RadOnc conversation I've ever heard.

How do y'all feel about bladder hot spots that are within the urine on planning?

Where's the misunderstanding here? I don't care about hotspots in the implant. In simple terms, not asking the planning software to deliver prescription dose to 250 mls of silicone/saline would seemingly not change the coverage where it matters while delivering fewer mu's. Seems safer, kinda like treating bladder cancer with an empty bladder. Though I don't want to ruin your analogy, however irrelevant. This isn't about sparing the implant. Why target something with 0% chance of having cancer in it? And my dosimetrists won't mind as I actually draw out my own ctvs.

 

[deleted1180461]

I do this to spare SMGs in cases where treating 1B is a clinical coin toss. My dosi wants to kill me every time. But there’s a reason behind it. It’s going to be way harder to control dose; let us know how it goes.

 

[TheWallnerus]

True, the center of the implant is certainly not CTV.

None of the implant is the CTV

Not a single molecule of the implant will benefit from a picogray

This is starting point for a planning goal

Pragmatism comes AFTER initial optimizations imho

You try this approach; if sucks a$$, abandon it

Debating sparing a breast implant is the most RadOnc conversation I've ever heard.

How do y'all feel about bladder hot spots that are within the urine on planning?

Urine trouble now

 

[Ray D. Ayshun]

Was able to find way into ESTRO guidelines, and it looks like they exclude the implant in prepectoral positioning

Post pectoral looks like a dream in that ribs etc get excluded by centimeters as has been said by Palex. A dosimetric paper was published in that context showing a not surprising decent reduction in ipsilateral heart and lung doses, though suprisingly, no difference in MUs despite a substantial reduction in PTV volume. In any case, I'll see how it looks in the prepectoral context.

 

[CurbYourExpectations]

Was able to find way into ESTRO guidelines, and it looks like they exclude the implant in prepectoral positioning
View attachment 388240
Post pectoral looks like a dream in that ribs etc get excluded by centimeters as has been said by Palex. A dosimetric paper was published in that context showing a not surprising decent reduction in ipsilateral heart and lung doses, though suprisingly, no difference in MUs despite a substantial reduction in PTV volume. In any case, I'll see how it looks in the prepectoral context.

From your paper: the dorsal part between the implant and the pectoral muscle/chest wall, containing eventual residual glandular tissue(Fig. 4C, blue contour): only to be included in case of thepresence of adverse tumour factors (Table 2).

ESTRO consensus guidelines for posterior portion of breast: Most caudal CT slice with visible breast.

I do not think any of this was based on IMRT and avoidance of possible breast tissue. But not a specialist in breast.
No indications that you should avoid it with IMRT based mechanisms, unless I'm mistaken. Let me know.

Edit: I enjoy the discussion and argument and appreaciate you Ray.
Edit: Are Radiation Target Volumes for Postmastectomy Radiation Therapy Too Large? Initial Report of the Complication Avoidance of Reconstruction Implant Radiation Therapy (CARIT) Study

 

[Ray D. Ayshun]

From your paper: the dorsal part between the implant and the pectoral muscle/chest wall, containing eventual residual glandular tissue(Fig. 4C, blue contour): only to be included in case of thepresence of adverse tumour factors (Table 2).

No indications that you should avoid it with IMRT based mechanisms, unless I'm mistaken. Let me know.

right. My initial question was just wondering if people cropped out the implant, and if it was helpful. In my case, the plan is to treat the rind more or less, as they've outlined here. My guess would be that the implant is still getting reasonable dose globally. Just less. And in turn, the ipsilateral lung is getting less. Could be wrong. At the same time, if your coverage constraint is 95/95 when the implant is included, I suspect the implant can pretty easily be covered almost completely by prescription dose. In my case, the implant is 60% of the PTV. In turn to get to 95%, just 35 of the remaining 40% need be covered, which is to say, 87.5% of the volume that actually needs to be covered is being covered.

 

[TheWallnerus]

The way optimizers plan these days you may full well avoid very high risk tissue by avoiding a giant blob of nothing in the middle. Are you guys avoiding contouring to the musculature for mastectomy patients (or giving full dose up to the musculature)? That is a bold move IMO, and not something I would want.

People trot out boogey man arguments for “don’t do this” in rad onc a lot and I have been known to myself sometimes.

But correct me if I’m wrong but contouring implant as CTV would violate ICRU-50. If there’s one thing I can’t stand it’s ICRU violators.

 

[Palex80]

None of the implant is the CTV

Not a single molecule of the implant will benefit from a picogray

You are absolutely correct.

 

[communitydoc13]

though suprisingly, no difference in MUs despite a substantial reduction in PTV volume

Why target something with 0% chance of having cancer in it?

not asking the planning software to deliver prescription dose to 250 mls of silicone/saline would seemingly not change the coverage where it matters while delivering fewer mu's

MUs are largely a function of segmentation and are normalized relative to a 10x10 open field. A CK plan targeting a tiny brain lesion may have an absurd number of MUs due to the dose being delivered through a tiny cone (that beam is on a long time). A heavily segmented plan targeting a smaller volume may require more MUs than a less segmented plan targeting a larger one.

It is not clear to me whether avoiding the implant or not is better for finding simple solutions to a breast plan that are delivering dose in a way that has been shown to work.

Lets say you include the implant in the CTV and have a 95/95 coverage criteria. There is expected build up under the skin surface and very simple solutions (tangents with a few segments) will get you coverage. Taking away the implant, you are now looking to get 95/95 to a thin slice of tissue between the implant and the body surface. This is going to require a more difficult solution and you may be driving to a plan that overdoses skin and subcutaneous tissue relative to standard.

For breast, I prefer simple solutions. For true IMRT breast, the issue is always the target volume. It might be appropriate to crop back a full 1 cm from the skin surface and RA everything (I suspect that we would have a hard time proving that this approach worse than any other strategy for breast cancer outcomes in the present environment of early stage diagnosis and good systemic therapy). This approach would of course give you a wonderful toxicity profile (although at times you will still be overdosing the heart relative to tangents). Now in this particular case, cropping back 1 cm from the skin surface would mean that you are only treating the implant!

 

[deleted1180461]

No one is arguing that the silicone or saline might harbor tumor cells and needs to be in the CTV. This is a dosimetry question. If you carve a hole in your whole breast target volume and try to use arcs with inverse planning with the implant goo as an avoidance structure you're gonna have a bad time.

 

[Ray D. Ayshun]

MUs are largely a function of segmentation and are normalized relative to a 10x10 open field. A CK plan targeting a tiny brain lesion may have an absurd number of MUs due to the dose being delivered through a tiny cone (that beam is on a long time). A heavily segmented plan targeting a smaller volume may require more MUs than a less segmented plan targeting a larger one.

It is not clear to me whether avoiding the implant or not is better for finding simple solutions to a breast plan that are delivering dose in a way that has been shown to work.

Lets say you include the implant in the CTV and have a 95/95 coverage criteria. There is expected build up under the skin surface and very simple solutions (tangents with a few segments) will get you coverage. Taking away the implant, you are now looking to get 95/95 to a thin slice of tissue between the implant and the body surface. This is going to require a more difficult solution and you may be driving to a plan that overdoses skin and subcutaneous tissue relative to standard.

For breast, I prefer simple solutions. For true IMRT breast, the issue is always the target volume. It might be appropriate to crop back a full 1 cm from the skin surface and RA everything (I suspect that we would have a hard time proving that this approach worse than any other strategy for breast cancer outcomes in the present environment of early stage diagnosis and good systemic therapy). This approach would of course give you a wonderful toxicity profile (although at times you will still be overdosing the heart relative to tangents). Now in this particular case, cropping back 1 cm from the skin surface would mean that you are only treating the implant!

Sure, agreed on translating volumes to MUs. I remain a little bothered by how much the machine sounds like a geiger counter at Chernobyl during SBRTs. That said, my surprise was based on the general appearance of the following plan from the publication. Just seems like the one on the left would be delivering fewer MUS.

And my initial question is based on this. I again, have never mentioned an avoidance structure. Rather a simple yes, no, I don't know question: Is it safer to treat the volume on the left?

Larry David was correct, though, as this is very radonc discussion. Essentially, some other question was answered, and the end result is, things are fine as they are...

 

[TheWallnerus]

No one is arguing that the silicone or saline might harbor tumor cells and needs to be in the CTV. This is a dosimetry question. If you carve a hole in your whole breast target volume and try to use arcs with inverse planning with the implant goo as an avoidance structure you're gonna have a bad time.

No you won’t (especially in the case of inversely optimized two field opposed tangent IMRT), and I don’t think it will help much to carve, but I’d like to see.

 

[TheWallnerus]

That said, my surprise was based on the general appearance of the following plan from the publication. Just seems like the one on the left would be delivering fewer MUS

The reason we don’t see MUs correlate with volume is due to the physics definition of a gray itself: joules per kilogram. As an extreme example, think of whole body 8 Gy wide open field and 8 Gy to a 10x10 open field… same MUs. There are simply more given photons in the former than the latter (because we relatively unimpeded their egress from the linac in the former versus the latter).

 

[communitydoc13]

Just seems like the one on the left would be delivering fewer MUS.

MUs are mostly a measure of beam on time, not dose delivered to target or integral dose. Beam on time correlates well with dose delivered in the unsegmented setting using the same open field, however, once you start modulating an open beam, the correlation is overwhelmed by other factors. A wedged plan alone will require more MUs to deliver the same dose to target.

Now in the extreme, I do wonder about MUs as they creep up above a factor of 4-5x prescription dose for segmented plans (this concern would not apply to something like a CK format). There are always uncertainties, and uncertainties almost always compound.

Regarding your above volumes...it's just that nobody (or very, very few) have been treating the volume on the left. So if you are looking for adequate coverage, you don't really have a good convention to lean on to determine what this is. (e.g. we all know that RA plans give pretty good dose to skin without bolus, but we don't really know what it is...we do know that others crop volumes 3-5 mm from skin surface and things work out).

As an extreme example, think of whole body 8 Gy wide open field and 8 Gy to a 10x10 open field

Not sure about this...there is a correction for different field sizes. (a larger field does not actually need to be on quite as long to deliver dose to a certain point at depth due to contributions from that entire larger field... in other words, the output factor goes up). None of us do hand calcs anymore, but the newbies probably should know this for boards!

 

[deleted1180461]

No you won’t (especially in the case of inversely optimized two field opposed tangent IMRT), and I don’t think it will help much to carve, but I’d like to see.

We're talking about 2 different questions here. Having to cover the tissue behind the implant vs. excluding it completely because it's behind the muscle.

Yes, if we're talking about a patient with breast augmentation that needs whole breast radiation and the implant is behind the muscle, it makes complete sense to contour the breast tissue in front of the implant and deliver with VMAT (maybe you could even get it improved). I do this not infrequently, although usually with PBI. Treating a PMRT case and trying to direct dose away from the interior of the implant capsule is totally different question. First why are you doing it, and second what is the dose in the tissue touching the capsule going to look like vs. keeping the whole as the CTV.

 

[evilbooyaa]

right. My initial question was just wondering if people cropped out the implant, and if it was helpful. In my case, the plan is to treat the rind more or less, as they've outlined here. My guess would be that the implant is still getting reasonable dose globally. Just less. And in turn, the ipsilateral lung is getting less. Could be wrong. At the same time, if your coverage constraint is 95/95 when the implant is included, I suspect the implant can pretty easily be covered almost completely by prescription dose. In my case, the implant is 60% of the PTV. In turn to get to 95%, just 35 of the remaining 40% need be covered, which is to say, 87.5% of the volume that actually needs to be covered is being covered.

Do not include the implant in the CTV (as long as it's posterior to the muscle). As you have mentioned, do not constrain it, it's just not a target structure. Gets dose, doesn't get dose, whatever. Usually not an issue when people do 3D, but obviously matters w/ IMRT/VMAT.

MUs will be similar. Lung dose may be slightly better. Heart is unlikely to be significantly effected would be my overall guess.

I fully agree with the bolded. A smaller PTV is harder to meet 95/95 coverage on compared to a larger PTV (assuming the middle cavity is not an avoidance structure).

 

[Ray D. Ayshun]

Do not include the implant in the CTV (as long as it's posterior to the muscle). As you have mentioned, do not constrain it, it's just not a target structure. Gets dose, doesn't get dose, whatever. Usually not an issue when people do 3D, but obviously matters w/ IMRT/VMAT.

MUs will be similar. Lung dose may be slightly better. Heart is unlikely to be significantly effected would be my overall guess.

I fully agree with the bolded. A smaller PTV is harder to meet 95/95 coverage on compared to a larger PTV (assuming the middle cavity is not an avoidance structure).

Re subpectoral implants, these are target and OAR findings from paper I mentioned. Haven't seen anything published re prepectoral implants, which entails targeting a rind around the implant. EA = only targeting tissue anterior to the implant

 

[TheWallnerus]

Re subpectoral implants, these are target and OAR findings from paper I mentioned. Haven't seen anything published re prepectoral implants, which entails targeting a rind around the implant. EA = only targeting tissue anterior to the implant

View attachment 388374
View attachment 388375

If one is painting the sea, one should use the color blue. If we analyze the average square surface area covered by blue in the sea paintings of Hokusai versus Monet, Hokusai uses significantly more blue. This proves Hokusai is better at painting the sea, and perhaps better at painting in general; more research is needed.

 

[Ray D. Ayshun]

If one is painting the sea, one should use the color blue. If we analyze the average square surface area covered by blue in the sea paintings of Hokusai versus Monet, Hokusai uses significantly more blue. This proves Hokusai is better at painting the sea, and perhaps better at painting in general; more research is needed.

At this point, I'm just dragging things out for ****s and giggles as breast remains the worst. My original question can be rephrased now to: who is drawing the CTV on the left for PMRT in patients with immediate reconstruction and a prepectoral implant?

I think the corollary question is, who wasn't told what a CTV is as a PGY-2 and is targeting the CTV on the right? Fwiw, I was taught to target the volume on the right. If it makes no difference dosimetrically, and it appears to in the subpectoral context, then fine, it's moot. It still violates first principles, though, to call something with a 0% chance of harboring cancer cells a CTV. The ESTRO contouring guidelines seem to support this approach, while the RTOG continues to party like its 1999. This perhaps explains why much has come from ESTRO of late, while RTOG continues to find ways to treat this volume:

 

[evilbooyaa]

I would draw the CTV on the left, because I was taught what CTV means during my residency training, rather than just evaluating 3-field plans without any volumes on my breast rotations.... yes with 3D volumes don't really matter most of the time for a 3-field plan, but we obviously know they do w/ IMRT.
But also, a pre-pectoral implant as a recon choice for someone planned for (or potentially undergoing) PMRT is really suboptimal. Ideally just place it post-pectorally so you can just treat anterior rind and minimize lung dose.

 

[Mandelin Rain]

I didn't want to start yet another breast thread, but.....

How liberally are people applying B51 currently? Premenopausal? Triple Negative? "Multiple suspicious" (only one biopsied) LNs pre-chemo?

This isn't a great pre-publication B51 patient, right?

 

[radoncftw]

I didn't want to start yet another breast thread, but.....

How liberally are people applying B51 currently? Premenopausal? Triple Negative? "Multiple suspicious" (only one biopsied) LNs pre-chemo?

This isn't a great pre-publication B51 patient, right?

waiting for the full publication before i apply.

 

[TheWallnerus]

I didn't want to start yet another breast thread, but.....

How liberally are people applying B51 currently? Premenopausal? Triple Negative? "Multiple suspicious" (only one biopsied) LNs pre-chemo?

This isn't a great pre-publication B51 patient, right?

Walk through the logic of why not a great pre-pub B51 patient if you would be so kind, because else I’m making assumptions… like I assume if there were a publication the patient would be a great B51 patient??

 

[TheWallnerus]

waiting for the full publication before i apply.

What sense does this make.

 

[TheWallnerus]

Depending on what assumptions one makes, beta (type II error) for a ~1600 patient study with the p-values found in this study for the primary (IBCR-FI) and secondary (OS) measures, which were in the p=0.5-0.6 range... the beta would approach zero or parts per trillion or some ridiculous number like that. So waiting for a publication will do nothing to the results of this study (i.e. the study failed to reject the null which is that radiation in general does not help N+ patients who become ypN0) and is delusional thinking imho to keep using RT on these women. The stats probabilities are ~100% that the publication results will match the abstract. Thus the stats probabilities are ~100% that RT hurts here... now, before publication, and at all time points in the future. We already "knew"* that RT doesn't help OS for N+ breast cancer on the basis of multiple trials, and should have been Bayesianly suspicious that it would not help local control in ypN0. The suspicion is now well-confirmed.

*of course this can be debated

 

[deleted1180461]

 

[Mandelin Rain]

Walk through the logic of why not a great pre-pub B51 patient if you would be so kind, because else I’m making assumptions… like I assume if there were a publication the patient would be a great B51 patient??

I didn't mention, but she'd be mastectomy and I believe there was a "trend" toward improvement in mastectomy patients (would like to see data). 1 vs 3 enhancing nodes, primary size, primary response, etc... I don't think any of that specified in abstract. She's a very young patient and I'd rather err on the side of overtreating than undertreating. Particularly with incomplete information.

 

[taserlaser]

What sense does this make.

Our group has decided to wait for the publication before implementation in practice, though we do discuss with patients. More of to have something tangible to defend the decision of omitting RT. Wouldn’t expect stats to change but full details are nice to know. The whole change adoption curve in practice - our group is slow…

 

[TheWallnerus]

Our group has decided to wait for the publication before implementation in practice, though we do discuss with patients. More of to have something tangible to defend the decision of omitting RT. Wouldn’t expect stats to change but full details are nice to know. The whole change adoption curve in practice - our group is slow…

Otoh. I saw people adopt MA20 and EORTC quite "liberally" (see below) just based on abstracts and presentations.

God, grant me the wisdom to accept the study results I like
the courage to disregard the study results I don't like
and the wisdom to know that the Red Journal doesn't publish practice-changing results anymore

 

[HolySmokes]

I have always been suspicious of how limited the benefit of RNI was for patients in general, so I have personally started omitting in B51 eligible patients (with mastectomy, obviously still treating the breast with BCS). Although I do talk to them about how we only have an abstract, don't have details from full publication, etc etc. So far even with that caveat no one has decided to pursue RT.

 

[drowsy12]

the machinations people are doing to avoid believing b51 are hilarious to me. it makes complete and total sense! the study findings are not surprising! believe your lying eyes!