At first, the rough patch on the roof of Mike’s mouth didn’t seem like anything to worry about. It didn’t hurt. But it didn’t go away. His dentist referred him to an ear, nose, and throat doctor who did a biopsy, which was inconclusive.

So far, that didn’t sound so bad. But when Mike followed up with an oral surgeon, he got a diagnosis that is the stuff of nightmares: He had a rare, life-threatening cancer of the salivary gland called adenoid cystic carcinoma. Standard treatment in the United States is surgery of the palate, followed by radiation therapy.

Mike learned it would take as long as 14 hours to surgically remove the tumor, which grew rapidly to the size of a ping pong ball beneath the palate. He could lose the ability to speak or swallow, at least temporarily. Even then, he faced a high chance that the cancer would eventually metastasize, probably to his lungs. Untreated, it could spread to his brain.

“I don’t have a fear of death. It’s a fear of living badly,” says Mike, 63, an advertising professional. “That’s what drove me to find other treatment options, the fear of being a shell of myself.” (Concerned about his medical privacy, he asked to not use his full name.)

In his fear-fueled research, Mike discovered an alternative to surgery that might kill the cancer and prevent its future spread: carbon ion therapy. Like traditional radiation, carbon ion therapy damages the DNA of fast-growing cancer cells, ultimately destroying them. But unlike older forms of radiation, this technique causes minimal harm to normal tissue. It also works against tumors that are resistant to x-ray treatment, and studies suggest it triggers an immune response against cancer.

Globally, carbon ion therapy is viewed as the next horizon of cancer care. About 22,000 patients have received the treatment at 13 centers in Germany, Austria, Italy, Japan, and China. More locations are under development in South Korea, Taiwan, and France.

Yet the therapy has followed an odd trajectory in the US. Although it was developed in California in 1975 and early research pointed to its advantages, not a single carbon ion facility, not even a research-oriented one, exists in the US. Other countries invested public money in the technology, but so far, American proponents of carbon ions have been unable to garner federal construction money or sufficient private backing.

What’s flourished instead is a related approach called proton therapy, which also uses charged particles and has some of the same benefits. Today, 31 US proton centers offer treatment for cancers in areas where radiation damage to surrounding normal tissue could be dangerous or even deadly, such as tumors at the base of the skull or tumors in young children.

Carbon ion therapy is similarly precise, but because carbon ions are heavier, they deliver more cancer-killing power than protons do. Carbon centers have reported impressive survival rates, particularly for hard-to-treat bone and soft-tissue cancers such as spinal tumors.

The therapy involves accelerating carbon ions to two-thirds the speed of light, then “painting” a tumor with the radiation beam. Accelerated particles deliver their energy in a sort of delayed burst called a Bragg peak, so that very little damage occurs to normal tissue as the beam enters the body in a thin stream at a high velocity, and the killing power is concentrated on the tumor, where the particle track stops. (Traditional radiation damages tissue as the beam enters and exits the body, although radiologists use techniques to minimize the damage.)