I am arguing that 26 Gy is a standard PBI dose.
It's difficult to make a convincing case that 26 Gy is apt to show better toxicity outcomes versus 30 Gy. It's impossible to make a convincing case it would have worse toxicity outcomes.
It's difficult to make a convincing case that 30 Gy is apt to show better LC outcomes versus 26 Gy.* It's impossible to make a convincing case it would have worse LC outcomes.
Improvements in LC via RT in essentially every single trial (excluding meta-analyses, granted) iirc came with no improvements in OS, but some worsened toxicity.
So, all the above means: 26 Gy is a standard PBI dose.
* in one hypofx breast RT study of 2000 women, an increased RT dose to the tumor cavity was associated with a perfectly zero increased chance of LC:
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