Partial breast EBRT

[Reaganite]

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Was just wondering how you all do EBRT partial breast. I've only done mammosite-type pb, but my perm position will not have breast brachy, so I'm assuming I'm gonna be doing EBRT. I've read various different techniques (supine vs prone; alignment to skin marks only vs. clips vs. cbct), and just wondered what you all are doing...

 

[medgator]

Not doing it much off protocol. Out of all of the APBI techniques, it has the least F/U and experience. I'd probably feel more comfortable sticking to hypoFx instead of that if I couldn't do a SAVI (current practice has HDR so I do that)

 

[deleted4401]

I don't know how to do it, as I have never done it before. If there isn't a well defined seroma cavity, not sure how you'd identify cavity. The preliminary review of B39 showed good toxicity outcomes (unlike some of the single institution data), so if done correctly probably works pretty well.

Question, though ... Knowing that it is far less conformal than the other techniques, why is the dose to PTV per fraction higher than with brachy?

S

 

[Neuronix]

Was just wondering how you all do EBRT partial breast. I've only done mammosite-type pb, but my perm position will not have breast brachy, so I'm assuming I'm gonna be doing EBRT. I've read various different techniques (supine vs prone; alignment to skin marks only vs. clips vs. cbct), and just wondered what you all are doing...

I've got an abstract on our single institution experience with 3D CRT for APBI accepted as a poster for upcoming ASTRO. PM me if you want to meet up and talk in person.

We're essentially following B-39 protocol with slight modifications. We do supine in vac loc with tattoos, daily cone beam guidance. More commonly providers are using kV orthogs with 1cm PTV. With the cone beam we feel comfortable with a 5mm PTV.

I don't know how to do it, as I have never done it before. If there isn't a well defined seroma cavity

I've also been concerned about the question of "what if you can't tell where the tumor was?", but this hasn't been an issue in my limited experience. Our surgeons also always place clips.

 

[Palex80]

Some people may feel irritated by this post, but here it goes anyway...

Why do a CBCT for EBRT-PBI? You don't usually perform a CBCT for 3D-boost after WBRT, do you? Why do you feel less comfortable in the EBRT-PBI setting with skin marks than you are in the 3D-boost-post-WBRT setting?

We seldom do EBRT-PBI, unless our patients specifically insist having it or there are some other rare factors who favor PBI (last month we had a pacemaker patient, who didn't want her pacemaker repositioned; PBI was quite useful for her, since the pacemaker would have been inside the tangents if she was to receive WBRT). We are probably going to start doing EBRT-PBI a lot more often next year.
So far we have been designing the cavity as CTV and giving a 1cm margin to it.

Since experience with post-PBI cosmesis in the 3D-EBRT setting is limited, I am an advocator of 15 x 2.66 = 39.9 Gy (basically the START-B WBRT-schedule).

 

[Neuronix]

Why do a CBCT for EBRT-PBI? You don't usually perform a CBCT for 3D-boost after WBRT, do you? Why do you feel less comfortable in the EBRT-PBI setting with skin marks than you are in the 3D-boost-post-WBRT setting?

The concern is two-fold. First, the higher density of dose--i.e. 3D CRT APBI 3.85Gy BID for 5 days vs. 2 Gy daily fractions for 5 - 8 days. This presents several issues. We presume the less breast this high dose per fraction is delivered to, the better off the long-term result. Thus, we are trying to make the margin as tight as possible. Also any small amount of miss in theory provides more damage to the surrounding tissue. Second, this is the primary and only adjuvant XRT. Any amount of miss could potentially result in a lower cure rate. This is as opposed to a boost which is extra XRT on top of the whole breast treatment.

Certainly we don't push patients strongly in one direction or another. We offer intra-op, WBRT with Canadian (Whelan) hypofractionation (2.66Gyx16fx), and WBRT with standard fractionation as well. It's a complicated discussion depending on the individual patient tumor and breast factors as well as patient preferences.

 

[deleted4401]

I just had a L side pacemaker patient today. She was older, 79, and had T1micN0 dz, wide margins. Getting Tam. I told her forget about RT. But, now I'm thinking, can scan and so some strange geometry. Or, maybe contour cavity + 1cm and given Whelan dosing?

S

 

[Palex80]

Thus, we are trying to make the margin as tight as possible.

So, is your CTV-PTV margin smaller if you are doing only EBRT-PBI than if you are doing a 3D-EBRT-boost?

Also any small amount of miss in theory provides more damage to the surrounding tissue.

I agree with that.

Second, this is the primary and only adjuvant XRT. Any amount of miss could potentially result in a lower cure rate. This is as opposed to a boost which is extra XRT on top of the whole breast treatment.

I understand this, but it sounds a bit as if you are uncertain where you are giving your 3D-EBRT-boost without a CBCT. 🙂

Certainly we don't push patients strongly in one direction or another. We offer intra-op, WBRT with Canadian (Whelan) hypofractionation (2.66Gyx16fx), and WBRT with standard fractionation as well. It's a complicated discussion depending on the individual patient tumor and breast factors as well as patient preferences.

That's very good. It's the right way to go until we have definitive answers to WBRT vs. PBI question.

 

[Palex80]

I just had a L side pacemaker patient today. She was older, 79, and had T1micN0 dz, wide margins. Getting Tam. I told her forget about RT. But, now I'm thinking, can scan and so some strange geometry. Or, maybe contour cavity + 1cm and given Whelan dosing?
S

If the geometry does not fit well for a 3D-boost, the tumor was rather superficial and no pacemaker wires are running under/close to the resection cavity, you could also simply use electrons and just to be certain place something on the pacemaker (like a can of sardines ), to limit dose by the escaping electrons from the sides of the tube.

 

[medgator]

I agree with most of what you said but wouldn't put intra-op in the same category was WBRT, Canadian, or even APBI. At least on this side of the pond, I think doing intra-op off protocol is pretty far outside the standard of care.

A lot of places are jumping on it though (at least in FL --- Moffitt, for example, was heavily advertising it before on the radio). I am not sure whether they are doing it on protocol or not, but AFAIK, there is only one randomized trial (TARGIT) that looks at intraop, and people are using it in all sorts of ways (either as a boost in lieu of a WBRT boost, or as a complete replacement of WBRT altogether).

I agree with you though. The data for intraop is sparse, and it really should be offered under the strictest of criteria, ideally in a protocol setting

 

[Gfunk6]

There is no Category I evidence (yet) supporting APBI. However, intra-op does have Category I evidence (TARGiT). Therefore, I think doing intra-op using the Intrabeam system off-protocol is appropriate but other forms of intra-op (like Xoft) need to be on protocol in my opinion.

 

[medgator]

There is no Category I evidence (yet) supporting APBI. However, intra-op does have Category I evidence (TARGiT). Therefore, I think doing intra-op using the Intrabeam system off-protocol is appropriate but other forms of intra-op (like Xoft) need to be on protocol in my opinion.

Its a single study with a relatively short F/u period. I would still remain cautious in younger patients and/or more aggressive disease profiles as the median age in the study was 63 and they were mostly t1, g1/g2 tumors

 

[Neuronix]

So, is your CTV-PTV margin smaller if you are doing only EBRT-PBI than if you are doing a 3D-EBRT-boost?

It actually works out to be the same in our schema.

I understand this, but it sounds a bit as if you are uncertain where you are giving your 3D-EBRT-boost without a CBCT. 🙂

I see your point on this. A miss is a miss and is always unacceptable, of course. My point is that I feel a little more comfortable with the undesired possibility of a miss on a boost given that it's a smaller fraction and is supplemental therapy after whole breast treatment. Again, our particular study protocol uses a smaller PTV than B39, and thus we can justify a smaller V50% constraint. We hypothesize that irradiating less breast tissue will lead to better cosmetic outcomes, and that's how we justify using CBCT.

The B39 protocol is as follows:
(http://rpc.mdanderson.org/rpc/credentialing/files/B39_Protocol1.pdf):
"The CTV will be defined by uniformly expanding the excision cavity volume by 15 mm. However, the CTV will be limited to 5 mm from the skin surface and by the posterior breast tissue extent (chest wall and pectoralis muscles are not to be included). The PTV, defined as a uniform 10 mm expansion of the CTV, will provide a margin around the CTV to compensate for the variability of treatment set-up and motion of the breast with breathing."

If you're using that, you probably don't need CBCT.

Its a single study with a relatively short F/u period. I would still remain cautious in younger patients and/or more aggressive disease profiles as the median age in the study was 63 and they were mostly t1, g1/g2 tumors

I am 100% on board with this statement. We are very picky about to whom we offer intra-op or 3D CRT APBI. I didn't mean to imply that every patient gets offered those treatments. Indeed, it's a fairly small minority I even discuss partial breast treatment with.

 

[Palex80]

Again, our particular study protocol uses a smaller PTV than B39, and thus we can justify a smaller V50% constraint. We hypothesize that irradiating less breast tissue will lead to better cosmetic outcomes, and that's how we justify using CBCT.

Ok, that makes sense.