High-Energy Particles Halt Spread of Certain Cancers
Researchers say that beams of high-energy particles are effective in stopping the spread of certain cancers in nearly all patients who have rare tumors for which there is no other treatment.
Doctors at the University of California, San Francisco, and Lawrence Berkeley Laboratory irradiated tumors of the eye, brain and areas near the spine with helium ions--helium atoms that were stripped of their electrons.
Such cancers afflict an estimated 2,500 Americans each year.
Using the particles produced by the lab’s 184-inch cyclotron, scientists were able to save the eyes of 182 of 190 patients treated in the past seven years, said Dr. William Saunders, a radiotherapist at UC San Francisco and the Berkeley laboratory. He reported his findings last week at the Symposium on Heavy Charged Particles in Research and Medicine.
The rare cancer, called ocular melanoma, is currently treated by removing the eye. Even then there is a 50% chance of recurrence within five years.
But the cancer reappeared in only eight of the 190 patients treated with the helium ions. Two-thirds of all of the patients retained normal eyesight or eyesight correctable to at least 20 over 100.
Researchers also found that heavy-ion therapy, under development for 30 years, was effective in treating 14 of 19 patients with tumors in very sensitive areas, such as near the spinal cord.
“The big advantage of these particles as compared to more conventional forms of radiation used in medicine, like X-rays, is that heavy ions deposit most of their energy at the point where they stop,” Saunders said.
Tissue three millimeters from the area of maximum radiation receives almost no radiation, he said.
In treating 546 patients with various types of cancer over the past 10 years, the researchers found that large tumors that are resistant to conventional radiation therapy--such as cancer of the pancreas or esophagus--did not respond well to helium-ion therapy.
Typical helium-ion therapy lasts eight days, with five separate radiation sessions of about one minute each, Saunders said.
Doses of up to 8,000 rads--the equivalent of more than 1 million chest X-rays--are deposited in the tumor. The size of the eye tumors ranged up to 20 millimeters across--about the size of a quarter--and up to 12 millimeters thick, Saunders said.