Have you ever seen footage of a white blood cell taking apart a cancer cell? This is worlds closer to unlocking that power than hoping a stray radioactive particle bumps the right lever. Perhaps the need for two separate medicines/agents to make this special cocktail and trigger the perfect immune response has been the elusive part?

Could you link to some footage of a white blood cell taking apart a cancer cell?

Yeah, this is an NK cell triggering an apoptotic (self-destruct) response in a cancer cell. So it's basically sending a kill-signal to the cancer cell, which then kills itself. This doesn't work for all cancers, though. In fact, one hallmark of cancer is unresponsiveness to apoptotic triggers.

Ok, here's one with T-cells from Cambridge University: https://www.youtube.com/watch?v=ntk8XsxVDi0

Iodine is critical to at least one of the pathways to apoptosis, and has been found to cause (allow?) it in several types of cancer.

As someone commented on that Youtube video: "I love watching cancer die. Great video!". Me too!

Yes but can it be done with minimal side effect?

Curing cancer with a bullet works too but the host suffers some adverse side effects.

I'd be careful calling the immune approach easy. Triggering a systemic immune response can also kill you very quickly.

Considering that chemotherapy is basically feeding poison to your organism in the hope that cancer cells (which are more active) will ingest it in higher quantity, I'd say that we have a pretty high tolerance threshold in term of side-effects while we are looking for an alternative.

As I understand it, most chemotherapy targets only dividing cells. In adult humans there are relatively few of these: cancer cells (which you want to kill), bone marrow (produces blood cells, so you have to monitor blood cell counts during chemo), and reproductive organs (produce gametes, so you may want to freeze sperm/eggs before chemo).

all things considered, it's probably far more dangerous than chemo in the sense that it could kill you or seriously and permanently injure you with your first dose depending on your phenotype. at least chemo is a slower process.

but immunotherapies don't kill most people, thankfully. there are also many ways that you could assay the patient to see how they might react to immunotherapy, but i dont know whether these are done clinically or not.

I think the name for this is

https://en.wikipedia.org/wiki/Cytokine_storm

Yes, radiosurgery can be done with low risk of side effects.