Sharpshooter Radiation Takes Aim at Disease

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A technical findings brief from the Department of Health and Human Services reports a new method to target cells that are “anatomically adjacent to vital organs,” that may in the future, take radiation therapy, typically a balancing act of “taking the good with the bad,” to one that echos the physicians creed — “do no harm.”

Research on a novel mode of radiation therapy was announced over the weekend by the HHS Agency for Healthcare Research and Quality.

While conventional radiotherapy — ionizing photon beams — kills cancer cells by interfering with the cellular DNA and affecting subsequent chemical processes that kill the cell, it also affects the surrounding tissue. As technology and understanding of subatomic structures has evolved, today’s most sophisticated technique uses high radiation doses of these photon beams in a mode called intensely modulated radiation therapy (IMRT).

With IMRT, the radiation is delivered via computer assistance to attack the tumor in a contoured, three-dimensional rather than a two-dimensional (width and height) mode. By varying the intensity of multiple beams the radiation passes through and around healthy and/or sensitive tissues, sparing them, until it reaches the final targeted tumor site. It’s targeted delivery reduces effects of repeat radiation, particularly important in pediatrics

Now, AHRQ reports researchers have studied the success of using an alternative ion particle to do the job, instead of photons. In the process of “ionizing” a particle, the energy structure of a particular atom or molecule is changed and is charged with another element. Researchers evaluated the efficacy of charged particles of helium, carbon or other ions which they say have different “depth-dose distributions when compared to photons.” (Imagine the difference between dropping a conventional golf ball versus one made of lead from the same height into a tub of soft clay.)

Because ionized particles can penetrate deeper, and the energy can be precisely controlled, they have the potential to deposit more radiation on the target, with fewer adverse effects to healthy tissue. The investigators say both the shape and the depth of the radiation can be computer-configured so that it will deposit the final dose of energy in a trajectory — known as the Bragg peak — as it reaches its destination.

Researchers say that further randomized studies are needed to evaluate this procedure, which is currently limited by the high cost of particle-beam technology, to only six hospitals in the U.S. A two-story cyclotron accelerator arrived in Philadelphia from Belgium in January and will open in 2009.

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