anatomy contouring  here or here

Based on the studies below, it appears that radiation combined with chemoRx (5FU + Mitomycin see data, or perhaps new regimens that contain Platinol, see data produce the best results. Other recent data is here. (Cisplatin may be less toxic than Mitomycin, see MD Anderson study.) The proper dose of radiation is unknown. The original trials (Nigro) used low doses (30Gy) but the standard has become 45-50Gy plus or minus a boost dose (9Gy if + bx or in some protocols a routine dose of 15-20Gy is added.) See recent MDA paper on technique here.

The RTOG tried to use higher doses (5940 with 2 w break) but had worse results than in studies with  previous lower doses (50Gy continuous.) The anal region tolerates radiochemoRx poorly and we generally are lucky to get in 5040cGy at 180cGy/fx. The necessity of a boost is unclear but if the response is poor, pushing to total dose to 54-59Gy is standard (see the current NCCN guidelines.)

The approach at the U of Florida seems quite reasonable. (The current NCI page notes: "The optimal dose of radiation with concurrent chemotherapy to optimize local control and minimize sphincter toxic effects is under evaluation but appears to be in the 45 Gy to 60 Gy range.") See details of RTOG anal trial 9811 and RTOG 0529 and the results here.

Typical results using modern chemoradiation with IMRT are here and here.  Some of the older studies are here