If proton beam therapy has been around for a half century, why has it taken so long to offer it to patients on a significant scale?
Although the precision of proton beam therapy has been known for decades, applications were limited to a few anatomic sites (e.g., uveal melanomas and tumors of the brain and head & neck) because accelerators were not designed for treating patients (their energies were not sufficiently high to treat tumors found deep in the body), and because many tumors could not be visualized with sufficient precision.
