Would you ever offer a simultaneous integrated boost to the lumpectomy cavity with 5 fraction ultra-hypofractionated whole breast radiotherapy (2600 cGy in 5 fractions)?

Yes, it was delivered in the trial although with conventional fractionation. In practice, we do 2.5 x 4 or 5.2 x 1-2 fractions like RCR guidelines.

I routinely have offered whole breast to 26 Gy/5 fx with lumpectomy cavity SIB to 30 Gy with no difference in toxicity observed vs 26 Gy alone and approach SIB as I do APBI to that dose.