My radiation oncologist seemed to bounce between 5 and 28 days, implying that the choice was mine. I probed on why the shorter treatment wouldn't be everyone's choice. Less time. Same effect -- yes? Frankly, he wasn't able to provide a satisfactory answer. I was left with the impression that based on his hospital's experience, they were seeing little difference in the longer vs. shorter treatment options. Bottom line: The research and experience with the longer treatment span is extensive and proven. The shorter plan, while perhaps as effective and with no greater side-effects, is still being trialed in a fashion until they have definitive results.