I don't know the role of IMRT, but it is worthy of study, especially since the long term effects of chemotherapy and radiation therapy to the rectal bed endured by rectal cancer survivors are substantial.  Perhaps the place to start would be phase I/II IMRT with RT with concurrent capecitabine.  Although cape is said to be equal to 5FU in the R-04 study, the p value was 0.12 and cape might be better if the trial had more power.  From my experience, waiting longer is better; 8 or even 10 weeks is good, but I have no data for it.