Is there an advantage in treating with a SIB (simultaneous integrated boost) over sequential boost for anal cancer?

Radiation therapy, in almost everything we do, is a trade-off betweeen tumor control and toxicity. This gives us the opportunity to change dose and fractionation to obtain what we perceive as the "correct" balance between aggressiveness for tumor control and being conservative to preserve function and minimize toxicities. Asking about a SIB in anal cancer is just another way of asking whether we should be more aggressive in our dose/fractionation scheme in this disease. In order to answer the question one needs to weigh potential benefits in tumor control of a higher dose per fraction versus the risk of long-term anal sphincter dysfunction, bleeding and stenosis. If one thinks tha a higher effective dose should be given, the question that c...