Reoccurrence of this cancer are primarily because of incomplete primary treatment, (most commonly single discipline treatments in a non multidisciplinary environment) or a particularly aggressive version of SCC that responds incompletely to existing treatments.... and not scatter radiation. Micro mets to surrounding tissues locally and to the cervical nodes that are too small to be seen by any kind of scanning technology that we currently have, miss these until about 18-24 months post treatment, when they are big enough to finally show up on scans.

Scatter radiation is too low an amount to cause a cancer of its own, and the types that radiation causes (in higher doses) are not SCC. Radiation induced cancers, usually happen as mandibular osteosarcomas in about 3-5% of those treated with more than 70gys of radiation, and they occur about year ten after treatment. I personally fall into this risk group... thankfully 5% is a pretty low incidence rate.

Your previous posts though are areas where the greatest progress is being made, and that is in sparing collateral healthy tissues from damage such as the salivary glands, the carotids, spinal column etc. In both the technologies that you are considering, these are major benefits over older techniques.