I actually worked with MGH on their first proton treatment software for non cyberknife proton treatment. Later scaled it into AWS so their dosimetrists could iterate on treatment plans much faster. The initial treatments were incredibly successful and much easier on the patient, but theres no miracle either.

Patients still suffer adverse reactions, and you will have margins of error, not to mention you do not have unlimited time to develop a treatment plan that is perfect. It's a time/efficacy trade off and the goal is to hit as much of the cancer as possible, while maintaining a SAFE dose of radiation, not a zero dose. What is a safe dose? Well, the more aggressive your cancer the higher that number gets too.

Some patients still receive high dose radiation while on proton treatment simply because their cancer is that aggressive, typically suffering the same grade 1-2 diarrhea and vomiting as any other form of radiation.

Proton treatment is far superior for most cancers, especially deeper cancers like colon and prostate.

It's a living example of how tragic a new treatment option is, unfortunately proton centers are expensive to build and take years. So many people are still passing away from treatable disease and having to endure high dose chemotherapy in other cases.