An expensive prostate cancer radiation treatment known as proton beam therapy has just as many side effects as a more common and cheaper radiation method, according to a new study.

In terms of side effects, "In the long term, there's really no difference in outcomes between proton radiation and IMRT for men with prostate cancer," said lead author Dr. James Yu, a radiation oncologist at Yale University School of Medicine in New Haven, Connecticut.

Proton therapy advocates argue that protons blast radiation directly to the tumor and therefore avoid side effects. The more common "intensity-modulated" radiotherapy (IMRT) exposes some healthy tissue to radiation that researchers hypothesized would increase side effects and even additional cancers.After a year, however, the study found the same number of side effects among men who'd had both treatments.

Prostate cancer, the most common cancer in men, kills about 28,000 Americans each year. However, many men don't die of the disease, because many tumors grow very slowly.Treatments include chemotherapy, hormone therapy, surgery, and frequent surveillance - aka "watchful waiting."