You should be seeing a dental oncologist, if you are he's probably thinking 1.5 weeks in is still safe because the real pain usually doesn't start until around week 3 - however - your having chemo too I assume, so your immune system will be compromised, add to that the possibility of being hyper sensitive to rads - some people are... And it could be very uncomfortable, plus any extra small nicks while cleaning could cause infection etc... I'm with the others push to be cleaned earlier.