There are two aspects to your question. One is the thallium issue. I have to say that images with thallium are pretty good in today's world because the equipment has made a lot of progress. It's not the ideal trace, for the reason that I've mentioned, but it's a good temporary alternative.
As to your second question, about the fact that I've witnessed a lot of advanced cancer due to the lack of availability of PET scans, the answer is formally yes.