The National Cancer Center in Tokyo has unveiled a new weapon to treat cancers long considered unbeatable: neutrons that attack cancer cells only.

NCC says it hopes to launch clinical trials for the new radiation therapy, called Boron Neutron Capture Therapy (BNCT), by next March.

BNCT is a next-generation radiotherapy that is believed to be less invasive and easier to endure for cancer patients. It is administered in two steps. First, a patient is injected with drug compounds containing boron-10, which is known to accumulate in cancer cells. Next, low-energy neutrons are irradiated onto cancerous parts of the patient’s body. When neutron beams hit boron, it causes a nuclear reaction, decays into alpha particles and lithium-7 nuclei, and kills cancer cells in the process.

The alpha particles and lithium-7 nuclei travel such short distances — 9 microns and 4 microns, respectively — so they don’t destroy healthy cells around cancers.

BNCT is hoped to save people with cancers long considered hard or impossible to treat, including brain tumors and malignant melanoma, known as the most aggressive and life-threatening type of skin cancer.

While the idea of using neutrons for cancer therapy was originally conceived decades ago in the U.S., researchers in Japan have pushed it further and now lead the world in this field, NCC officials said at a news conference last month.

The center’s approach is unique in that it will use the “lithium target” system — a device to create neutrons by making lithium collide with protons created by a 4-meter-long, tubular machine called an accelerator.

Tokyo-based Cancer Intelligence Care Systems, headed by neurosurgeon Yoshio Imahori, developed the lithium-target system, while AccSys Technology, a U.S.-based subsidiary of electronics giant Hitachi, came up with the accelerator.

The ¥3 billion system will solve issues faced by other medical projects in Japan, NCC officials said.

“Japan has conducted BNCT research since 1968, but its clinical application was limited, because the only source of neutrons was nuclear reactors,” Dr. Jun Itami, chief of the radiation oncology department at NCC, explained at the press preview of the system in March.

Several hospitals in Japan experimented with the technology between 1998 and 2008, using the Kyoto University Research Reactor (KURR) in Osaka Prefecture and Japan Atomic Energy Agency’s JRR-4 reactor in Tokai, Ibaraki Prefecture. But both reactors were shut down for safety checks in the wake of the March 2011 triple-meltdown at the Fukushima No. 1 power plant. JAEA applied to the Nuclear Regulation Authority in December to dismantle the 50-year-old JRR-4.

“Nuclear reactors are not medical facilities. Plus, there are safety issues involved (in using nuclear fuels for clinical purposes),” Itami added.

The accelerator-based system, which is far more compact than a nuclear reactor, can be set up inside hospitals and requires no nuclear fuel to run. Use of lithium has improved the concept further, as it produces low-energy neutrons, which are less harmful to humans, NCC doctors said.

Researchers cite the less-invasive nature of the therapy, compared with chemotherapy, surgery or other types of radiotherapy, as its biggest strength. Patients need to get irradiated just once, which takes only about an hour.

Because it’s still a nascent technology, patient data for BNCT are limited. But findings so far have been encouraging.

A 2012 paper published in the Radiation Oncology journal, authored by Rolf F. Barth of Ohio State University and others, examined various clinical trials in Japan, Europe, Argentina and Taiwan. In one trial, conducted by Japanese researchers between 2001 and 2007, BNCT was found effective for 22 of the 26 patients with recurrent head and neck cancers, for whom there were no other treatment options.

The therapy at NCC, however, still has numerous hurdles to clear before it becomes available to the public.

First, it will take years for the researchers to get government approval, as both the equipment and drugs used need to be OK’d. The regulatory bar for the treatment will also be higher than normal as researchers are aiming to get it approved for everyone who succeeds in having boron-10 accumulate in their cancer cells, and thus not limiting its application to specific organs.

The cost of the treatment for patients is unknown at this point. Patients who will participate in the center’s clinical trials will not be charged, but it’s not clear whether the treatment, if approved, will be covered by the public health insurance system.

The therapy also cannot be used for cancers that are far away from the surface of the skin.

Still, researchers remain hopeful that it will prove popular, not just in Japan but overseas as well.

“We hope that the BNTC system — including the equipment, boron compounds and the PET scan that shows where boron accumulates in the body — can eventually be marketed overseas as a Made-in-Japan technology,” said Dr. Yasuaki Arai, director of the NCC hospital.

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