What is the maximum V20 on ipsilateral lung that can be safely accepted for 3 or 4-field breast plans?

We routinely treat the IM nodes so my comments reflect this practice:

1. I shoot for a mean ipsilateral lung V20 below 35%. This is achievable in most, though not all, plans.

2. The biggest driver of ipsilateral lung V20 is the amount of lung in the SCV field.

3. While it is tempting to raise the match line to decrease amoung of lung in the SCV field, one needs to be very careful about this because if the match goes too high, then the IFCV/Level III axillary nodes will be missed. In general, the matchline should be placed at the bottom of the head of the clavicle to ensure adequeate coverage of the level III axilla.

4. It is not clear to me that the ipsilateral V20 has been validated as a metric that predicts risk of clinical pneumonitis or...

I believe that the we sometimes forget about the other risk of lung radiation - secondary lung cancers. An older NSABP study and the following (Risk of second primary lung cancer in women after radiotherapy for breast cancer. Grantzau T; Thomsen MS; Vaeth M; Overgaard J. Radiotherapy & Oncology. 111(3):366-73, 2014 Jun.) suggest a real risk with long followup. The benefits of IM treatment (yet to be proved as not separated from regional node treatment in most studies) need to be weighed against risk. Minimizing the V20 is imperitive. I agree that much of the lung is often in the supraclavicular area. The upper axillary nodes can sometimes be treated in the upper tangents, which is helpful.

We try to keep the V20 below 30 percent for the ipsilateral lung and use different techniques to achieve that goal including matching electrons, an electron and photon combination, or photons alone.