If the problem is that his pain management program has mandatory drug testing, then vaporizing or ingesting marijuana is not going to solve it. It sounds like he cannot have any medical MJ at all in any form.
I can't imagine how he is smoking MJ either after cancer TX, I tried it once and the pain was unbearable so I bought a Volcano vaporizer right away. Sorry but I do not know of any article or citation I could send you a link to share. All the reputable studies and reports on smoking after cancer involve tobacco, not MJ.
In fact, the National Cancer Institute of the National Institute of Health (NCI at NIH) page on marijuana shows that there is no statistical evidence of marijuana causing any cancer. It does show how helpful MJ is for cancer issues but that's only because France did some studies. Sad to say, when you click on links - it shows zero studies being done (since the DEA won't allow them)
NCI on MJ
Sorry I can't help here.
Charm