When giving a breast boost, what are indications for a photon breast boost?

At what energy of electrons would it be better to use photons? How many fields and what field angles should be used for photon boosts? Do we worry about secondary malignancies?

2 Answers

Mednet MemberInvited Expert

Radiation Oncology · Varian Medical Systems/Allegheny health network

Answered on

In general, once the surgical cavity depth approaches 5 cm then it is harder to cover with electrons. That being said, for these patients with disease in the outer quadrant, the lateral decubitus position helps significantly to bring the cavity close to the surface. We published this data: http://www.ncbi.nlm.nih.gov/pubmed/23006598

Our use of photon boosts has gone down significantly since we started using this technique routinely. The cosmetic outcome is a function of integral dose to breast which is significantly higher with a photon than with electrons and for that reason, we try to avoid it. If we end up using photons, we do favor a multi-beam so that the dose is conformal and the spread of the prescribed dose is limited to the surgical bed with margin, and not to uninvloved breast tissue. We use high energy photons to achieve this.

Mednet Member

Radiation Oncology · USC Keck School of Medicine

Answered on

Agree with @Dr. First Last above.

With everything flipped upside down in the prone technique, however, the boost modality used is also switched to photon as default, with exceptional cases where patient is re-set up supine for electron boost portion if needed.

For vast majority of my cases, prone breast boost is done with photon mini tangents, usually in the same angles as whole breast tangents. This can be concomitant (if constraints for RTOG 1005 can be met, which is similar to published studies from NYU (https://www.ncbi.nlm.nih.gov/pubmed/22019349, https://www.ncbi.nlm.nih.gov/pubmed/27131077) The breast is stretched in the prone position and even if shooting through and through with mini tangents it ends up being a relatively small volume and cosmesis has been excellent in my experience.

If the cavity is too large for concomitant, then sequential boost can be used. Sometimes, couch kick in either direction for the mini tangents can help keep the boost isodose more conformal but I rarely do this due to its limited benefit and cumbersome planning and set up. When I do, I try to limit couch kick to max 12 degrees in either direction to avoid gantry clearance issues. With this technique, the lung and heart (and often even the chest wall) are outside of my field (as opposed to en face electrons) and get very little dose so I do not expect increased chance of secondary malignancy compared to baseline risk of any other breast radiation technique. I usually do not even mention secondary malignancy during consultation in those over 60 y.o. unless they specifically ask.