Do you prefer to use the FAST or FAST-Forward regimen when treating stage I breast cancer with an ultra-hypofractionated approach?  

We favor APBI like the Florence regimen but if technically not suitable, then FAST-Forward.

I offer all three (APBI, FAST, FAST-Forward) based on eligibility and let the patient decide.

While I don't make these schedules my primary recommendation, there are patients for whom the logistics make a big difference. In those cases, I will offer these regimens in low-risk disease without adverse features (like things I'd normally boost) and "normal" anatomy. I keep in mind the follow-up ...

As per the UK guidelines, and drawing on IMPORT-LOW and FAST-Forward, don't you think 26 Gy in 5 fr daily PBI is reasonable (and more compelling) as well for most PBI-eligible patients? In the FLORENCE trial, 30 Gy in 5f EOD was compared to 50 Gy plus boost 10 Gy, and only ~50% of the patients met t...

APBI is an excellent option for eligible patients. If they are not eligible for APBI by criteria, but they would qualify for FAST/FAST-Forward, I always prefer the FAST-Forward regimen, especially for patients coming from a distance. 

Based on patient preference: either APBI, FAST, or FAST-Forward. Based on personal preference: FAST (while using FAST-Forward constraints). Based on eligibility criteria on trials: the FAST eligibility (≥ 50 yo, pT1-2 pN0) more accurately represents the patient population at my clinic r...

The trouble for me is that not all the research is pointing in the same direction. With some trials demonstrating worse cosmesis and slightly higher IBTR or nodal failures with APBI and no serious downside to treating the whole breast, until we have better evidence, it makes sense to me to continue ...