Big boob, big cavity - when to not to boost..and stuff

[napoleondynamite]

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Do you guys have a cutoff or a ratio of lumpectomy cavity size to overall breast size that you use to determine whether a boost is "worth it?" What guides you in making the decision in the occasional patient when the boost would be most of the breast..?

What I saw in residency was that if the boost volume looked "too big," we would not do the boost. But I'm not sure how big is too big..or if there are other ways people handle that situation.

 

[Gfunk6]

I rarely saw large resection cavities. Where I trained, if a patient had a very large tumor then the surgeons would either offer neo-adjuvant chemotherapy first if the woman wanted to preserve her breast or mastectomy otherwise. Also, the overall trend with breast surgeons is to take out less tissue (see the recent editorial in the New England Journal).

In cases where resection cavities were larger than average, then it would not impact my decision to boost if needed. I would, however, tell the patient that her cosmesis would likely be poorer than normal and then go from there.

 

[deleted4401]

I never viewed size of the cavity as a factor in considering the boost. For IDC - boost almost everybody, except older woman (>70) that aren't in great shape and anyone treated with Canadian. For DCIS, threshold is a bit higher, but most of them get boosted. If an IDC patient had a close margin and a re-excision showed no residual disease, if there are no other adverse factors, I skip the boost. There is a paper on this. I don't know - we're doing all this for local control, and the boost is a component in reducing local failure, so I do it. But, for those that are more sparing with boost, totally makes sense because the cosmetic outcome is certainly worse.

I pretty much do 50 + 10 in everyone (once in a blue moon I can't meet constraints and it's super hot, then do the 45 + 16), but there was a paper in Red Journal comparing 50 Gy in 2 Gy (no boost) to 45 Gy in 1.8 Gy + 16 Gy boost, and the higher dose arm had better cosmesis. Can't wrap my head around that one.

 

[medgator]

I pretty much do 50 + 10 in everyone (once in a blue moon I can't meet constraints and it's super hot, then do the 45 + 16), but there was a paper in Red Journal comparing 50 Gy in 2 Gy (no boost) to 45 Gy in 1.8 Gy + 16 Gy boost, and the higher dose arm had better cosmesis. Can't wrap my head around that one.

Well the HypoFx studies showed either the same (Whelan) or better (START) cosmesis. Same deal

 

[deleted4401]

But this is saying that 61 Gy is better cosmetically than 50 Gy...

 

[medgator]

But this is saying that 61 Gy is better cosmetically than 50 Gy...

Yeah that is strange.

 

[iradi8u]

For those large cavities that would essentially make the boost close to whole breast, I don't boost. My attending just has a gestalt that I hope to one day understand well enough to make it my own. Til then, if I can see that the cavity takes up a huge portion of the breast, no boost.

 

[napoleondynamite]

For those large cavities that would essentially make the boost close to whole breast, I don't boost. My attending just has a gestalt that I hope to one day understand well enough to make it my own. Til then, if I can see that the cavity takes up a huge portion of the breast, no boost.

Yeah, that was what I saw from our breast attending too as a resident. I'm surprised to hear that it is apparently not a common practice in other areas of the country..

 

[Palex80]

I am not aware of any patients, who cavities were too big to boost. Usually the cavity is quite small and in the case of large primary tumors many of our patients get neoadjuvant chemo.
There are a couple of surgeons that tend to perform some kind of crazy rotational plastic surgeries in the breast, where once every now and then (1-2 times/year) we can't figure out exactly where the tumor cavity actually is.
In these cases we may choose to deliver a homogenous dose of 56 Gy in 2 Gy fractions to the entire breast and skip the boost. But, like I said, that's a seldom case.

Other than that I boost everybody who's younger than 60 and may skip the boost in over 60 year olds if they have pT1 and pN0 and non-G3 and non-L1 and R0 with at least 5mm margin and ER/PR positive. If they don't meet all these criteria, they get the boost.
I boost 10 Gy for most patients and reserve 16 Gy for R0 with <3 mm margin or high-risk young women (35 year old with a pT2 G3 triple negative-disease).

One interesting side-effect of 3D-planning for boost with photons is that the size of the boost tends to get bigger for some patients and smaller for others in comparison to the older standard electron boosts. Furthermore the boost may sometimes not be centered on the scar.
I was taught in my early-resident days to use a 6 cm round electron tubus for every T1 and reserve the 8 cm (or seldom 10 cm tubus) for T2s. I didn't plan the boost in 3D, I just looked at the planning CT-slide for the whole irradiation to estimate electron energy and often marked the field on the skin according to the scar / mammography.
I am starting to ask myself, how many of these boosts were actually done on the right place. 😕

 

[deleted4401]

Palex - there was a paper on that. People miss like 35% of the time with older techniques. Gotta plan with the CT scan.

One thing my partner does is add posterior margin, as well, so his energy is higher than mine on similar patients. He says PTV is PTV no matter what direction. It's true, but I didn't learn it that way. What do you guys do?

S

 

[napoleondynamite]

Other than that I boost everybody who's younger than 60 and may skip the boost in over 60 year olds if they have pT1 and pN0 and non-G3 and non-L1 and R0 with at least 5mm margin and ER/PR positive. If they don't meet all these criteria, they get the boost.
I boost 10 Gy for most patients and reserve 16 Gy for R0 with <3 mm margin or high-risk young women (35 year old with a pT2 G3 triple negative-disease).

That's a pretty impassioned defense of the boost 😉

My attending who would occasionally omit the boost always pointed out that the boost was not part of our hallowed B06 trial. Also, that the absolute benefit of the boost really is not all that big to begin with in women >50. When we're talking about a 2-4% benefit of LC, you have to treat 25-50 women with the boost to save on LR, etc, etc. Anyway, that is the flip side argument. Not saying it's right or wrong yet because really I feel too green to even have a strong opinion, which I why I'm asking what you guys all do, so thanks for the input.

I agree that omitting the boost should be rare. I probably saw it 3-4x per year during residency, usually on that pt who you were planning mini-tangents for the boost b/c the lumpectomy cavity was too deeply seated in a large breast for electrons. It's in some of those pts where you look at the dosimetry and realize you're treating 50% or more of the breast. I guess in that situation, it's worth considering if that 2-4% benefit outweighs cosmesis, which I think should be individualized as Palex is inferring.

 

[medgator]

Palex - there was a paper on that. People miss like 35% of the time with older techniques. Gotta plan with the CT scan.

One thing my partner does is add posterior margin, as well, so his energy is higher than mine on similar patients. He says PTV is PTV no matter what direction. It's true, but I didn't learn it that way. What do you guys do?

S

That's how I learned it as well. PTV is PTV. I account for the posterior margin with my energy

 

[napoleondynamite]

That's how I learned it as well. PTV is PTV. I account for the posterior margin with my energy

What PTV margin do you use?

 

[deleted4401]

Contour tumor bed, and then 1.5cm margin in all directions to account for penumbra/PTV. Don't account for posterior, but thinking I should.

 

[medgator]

What PTV margin do you use?

Generally 1 cm. That's used in multiple papers as well

 

[Palex80]

PTV is PTV, that's how I plan too and use 1 cm in all directions.

I have one more question for you guys: Do you plan the boost using the initial CT you used for the planning of the tangents or do you perform a new planning CT just before you start the boost?
The reason I am asking, is that sometimes there is some swelling in the breast and this may have an impact on boost setup with photons or energy selection for electrons.
I have considered advocating to start all treatments with the boost, rather than give it in the end of the treatment cycle, to bypass this problem , but my colleagues have been reluctant to implementing it.

 

[Gfunk6]

I have one more question for you guys: Do you plan the boost using the initial CT you used for the planning of the tangents or do you perform a new planning CT just before you start the boost?

Good question and point. I do not re-simulate patients for boost. However, I expand the resection cavity 1.5 cm (subtract bone, air, 4 mm skin). for my PTV so I'm pretty confident in not missing due to changes in breast anatomy. However, where I trained we sometimes placed women in a lateral decubitus position for boost to spare more non-boosted tissue and would re-simulate in those cases.

 

[napoleondynamite]

PTV is PTV, that's how I plan too and use 1 cm in all directions.

I have one more question for you guys: Do you plan the boost using the initial CT you used for the planning of the tangents or do you perform a new planning CT just before you start the boost?
The reason I am asking, is that sometimes there is some swelling in the breast and this may have an impact on boost setup with photons or energy selection for electrons.
I have considered advocating to start all treatments with the boost, rather than give it in the end of the treatment cycle, to bypass this problem , but my colleagues have been reluctant to implementing it.

We've typically re-CT'd in two situations for boost planning:

1) If re-positioning would be advantageous (i.e. a lateral position)
2) If the lumpectomy cavity was large or if there was a large-ish seroma up front

 

[medgator]

Generally 1 cm. That's used in multiple papers as well

We've typically re-CT'd in two situations for boost planning:

1) If re-positioning would be advantageous (i.e. a lateral position)
2) If the lumpectomy cavity was large or if there was a large-ish seroma up front

Never really did that for #1, outside of when we treat patients prone for whole breast and supine for the boost. Definitely do it for #2 when the seroma is quite large upfront

 

[RadRadRad]

RTOG 1005 has DVH guidelines for percent of breast receiving the boost dose as well as percent receiving 54Gy. I don't know if these are data driven, but it gives you a number to shoot for. They are pasted below.

Ideal: &#8804; 30% of the breast PTV Eval will receive &#8805; 100% of the boost prescribed
dose of 62-64 Gy (or 54.7-56.7 Gy if hypofractionated whole breast fractionation
used). Acceptable: &#8804; 35% of the breast PTV Eval will receive &#8805; 100% of the boost
prescribed dose of 62-64 Gy (or 54.7-56.7Gy if hypofractionated whole breast
fractionation used).
&#61607; Ideal: &#8804; 50% of the volume of breast PTV Eval will receive &#8805; 54 Gy (or &#8805; 46.1 Gy if
hypofractionated whole breast fractionation used). Acceptable: &#8804; 50% of the volume
of breast PTV Eval will receive &#8805; 56 Gy (or &#8805; 47.8 Gy if hypofractionated whole
breast fractionation used).

 

[jb2]

Yeah that is strange.

It is the whole breast dose that apparently makes the difference.