Why can’t everyone get a PET scan every year?


My former boss got lymph node cancer and had to get PET scans for years after he was in remission to make sure the cancer hadn’t spread. Why couldn’t everyone just get one PET scan every year as a routine check up instead of all the other multiple screenings we are subjected to? Especially because liver cancer, pancreatic cancer, lung cancer, etc, don’t have simple tests, like mammograms, to detect them?

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A PET/CT exposes you to about 25 mSv of radiation. This is equal to about 8 years of average background radiation exposure. That’s a huge amount, an 8 fold increase if you get one every year. That much radiation is harmful, unless there is a life-threatening condition that needs to be monitored.

I get CT Scans and X-rays twice yearly as part of my survivorship/monitoring post Testicular Cancer treatment. Not only are they really expensive but often you have to schedule them very far in advance. In addition to exposing you to some radiation and the cost, you would need to produce a lot more machines and train a lot more people to use them if you wanted everyone to get scans.

That said, scans of all varieties should be more accessible to people. Maybe not to the point where people get them every year, but if a doctor suspects something it shouldn’t take weeks or even months and thousands of dollars to get the proper scan.

These scans are quite expensive. Not only is the equipment and the people operating them quite limited and expensive but you also need people who are trained in interpreting the results. These radiologists are highly skilled in what they do but even then have a hard time finding issues unless they know what to look for. The body is just too complex and random. There are lots of different lumps and abnormalities in the body which might look like cancer. This also means that there are lots of false positives in these tests. A lot of people would be told they might have cancer and then have to go through a lot of other tests in order to confirm or deny this.

The better way of detecting cancer early is for people to pay attention to their body and when they notice symptoms discuss it with their doctor. The doctor can then do further examination which might discover other symptoms and then come up with a short list of things that could cause these symptoms. Then you can do expensive scans when you know what you are looking for. This is a much cheaper and more effective way of detecting cancer and other diseases.

There is actually quite a bit of debate about regular mammograms. Most people who get a positive result of the mammogram end up going through extensive screening including biopsies in many cases even though they end up not having cancer. Meanwhile most people with breast cancer find out by noticing new lumps in their breasts and then either on their own or on a recommendation from their doctor get a mammogram. So the regular mammogram screenings does not have the same effect in early detection of breast cancer as first thought.

PET scans are pretty expensive and work by injecting a bunch of radioactive material into you. It’s an acceptable cost for people who are suspected of having cancer, but if there’s no reason to think you have it, getting a PET scan is only going to make it more likely that you *get* cancer.

For every test, there must be a balance between :
– it’s effectiveness ( % of detection *when* there’s something)
– the false positives ( % of false results when there’s actually nothing)
– the costs

Blindly scanning a healthy population will results in tons of false positives, with unnecessary biopsies, emotion stress , etc

It’s much more efficient to target these tests to the population at risk

Not ELI5 but if you’re not adverse to a little maths

positives results : [%Eff x %Disease]+[%FalsePos x (1-%Disease)]

So even if the test 100% effective and only returns false positive in 1/100 of healthy cases, If a disease is rare enough ( 1/1000 in population), then ~10/11 of “positive cases” would be in fact healthy