Thank you KimK and Markus, and sorry to be so late.
We consulted a different radiation oncologist for IMRT, and after studying the case his response was similar to what KimK said. It being post-surgical radiotherapy, he said he couldn't be sure as to what specific areas to irradiate, and that it was safer to go ahead with the current mode (Theratron-780). That's what we've been doing, and trying our best to deal with all the problems that arise.

Thanks again, Merry Christmas and good health to all!