How many vertebral levels do you choose to treat with post-op RT?

There are many cases where patient has cord compression in 1-2 vertebral levels, but surgery was done with hardware encompassing 5-7 levels. Are you covering the entire extent of hardware and vertebral levels in this case? I understand the recent MSKCC study published suggesting to cover hardware reduces local failure, although this was in long bone metastases, not spinal.