Take a look at the OCF page on Trismus which is what Mickey means by "lock jaw" (which actually comes from Tetanus not radiation). Trismus OCF.
You will see that Trismus usually comes after the radiation TX. It's very common, even if you did yawn and stretch after each radiation TX. Good info on the OCF webpage.
I found the Therabite very helpful as this third round of radiation did bring back the Trismus.
Charm