I cannot give direct information on a particular patient without seeing them. AND this is a general medical question that the site is designed to answer! First, the real danger is if a patient does not tell her doctor all the chemicals she is exposed to. This comes up more with regular prescribed medicines than with illegal drugs surprisingly. GHB is perhaps the worst drug to interact with medical care. It is a strong depressant and will make other depressants (narcotics, sedatives, muscle relaxants, alcohol, everything used in anesthesia) far, far more likely to have someone stop breathing. Also, withdrawal from continual GHB use causes seizures and these are very difficult to prevent. That being said, radiotherapy MIGHT not involve either any other drugs nor a length of stay away from GHB that will produce withdrawal seizures if she just goes in and gets a treatment for an hour and comes right out. Ironically, the wait in the waiting room might be the most dangerous feature of radiotherapy. BUT if they merely give her a mild benzodiazepine with it as a sedative this could be fatal. Main advice is the doctors have to know the GHB is there.