What volume would you treat for an isolated axillary recurrence after BCS and whole breast RT who have resection of the recurrent disease?

In the case of prior whole breast (or chest wall only) radiation, I would typically only treat the nodal region after a isolated regional recurrence. The target volume should include at least the undissected axilla and infra/supraclavicular stations. I have not treated the IMNs after an isolated axillary recurrence. The dose would be 46-50 Gy in conventional fractionation usually. The full axilla may need to be treated if there are factors such as bulky nodes with extracapsular extension or tumor deposits in the axillary fat. In either case, close attention to any overlapping areas from prior breast treatment should be considered, and a homogeneous dose distribution developed.

In such situation, presuming breast imaging is normal, I have only treated regional nodal areas including level 1 and 2 and undissected level 3 and supraclavicular region

After resection of an isolated axillary recurrence, we would typically treat the regional lymphatics comprehensively but not re-irradiate the breast or chest wall. I would generally include the IMNs as they are at risk of harboring microscopic disease in the setting of a positive axilla and potentially aberrant lymphatics due to the prior breast conserving therapy. We tend to prefer pencil-beam scanning proton therapy in these situations because of the ability to minimize overlap with the prior whole breast radiotherapy fields while achieving very comprehensive coverage of the elective IMN CTV, which we define as the IMN vessels with a 4-5 mm margin based on a nodal mapping study we conducted (Jethwa et al IJROBP 2017). Importantly, the dos...