You said you cant really ask your doctor about smoking dmt, and maybe indeed smoking dmt would sound straight away too extreme to normal doctors... but... nowadays people are becoming more and more open to holistic/alternative therapies.. what if you say you heard of some amazonian drink called ayahuasca (which contains dmt, btw), and that there are ocasional reports of it possibly helping in cancer, that you would really like to try it but if he thinks that this dmt thing might be a problem.. If he says it could be a problem, ask if there is any evidence for it, any known cases, or if its a personal opinion..
Or/and...
Send an email to Rick Strassman and/or Charles Grob, two very good doctors who work with these psychedelic substances, they might have a better idea on your specific case and if its any danger.. They are busy people, though, so its not for sure that you will be answered, but give it a try, im sure their recommendation is worth more than that of anybody here, me included
Personally, I think you will not really have a problem, as the people above said, but thats just a guess and it shouldnt be taken as a recommendation.. Keep researching, and do tell us any updates on your situation..
All the best for you!
edit: the connection between pineal gland and dmt is only a hypothesis, its not proven.. what is known is that our bodies produce trace amounts of dmt during normal human metabolism but the connection with the pineal is uncertain, it might have nothing to do with it at all..