DOSES OF HIGH-ENERGY radiation from linear accelerators and so-called gamma knives can knock out malignant brain tumors. But these treatments are expensive and can damage surrounding tissue. Five years ago, scientific startup Photoelectron Corp. in Waltham, Mass., laid out a therapeutic strategy to attack metastatic brain tumors with greater precision and fewer side effects. Its approach, called the photon radiosurgery system (PRS), is now in full-scale clinical trials at Massachusetts General Hospital, Memorial Sloan-Kettering Cancer Center in New York, and other institutions. Early results show it to be an effective, economical tool to kill tumors other therapies can't reach.
With PRS, low-energy photons are injected into a tumor through a thin, 100-mm-long needle. It's inserted through tracks left by an earlier tumor biopsy, so there's no new trauma. Best of all, the X-rays are precisely calibrated to match the size and shape of the tumor, sparing healthy brain tissue. The entire procedure, taking 40 minutes, is completed in one shot, winning it the moniker "virtual outpatient brain surgery." At $500,000, PRS hardware is one-fifth the price of the conventional X-ray machines used to treat tumors. If the Food & Drug Administration approves, Photoelectron will expand clinical trials to include cancers of the breast, bladder, prostate, and other organs.