July 29, 2008 - Breathing is a major complication for radiation treatment of lung cancer.
The latest technology plans to tackle the problem by moving the radiation beam in unison with the breath. To help in the tracking, researchers have devised a new algorithm -- similar to one used by the post office -- that can predict where a tumor will be one second beforehand.
Breathing is a problem in radiation treatment not only for lung cancer, but also for cancers in other parts of the abdomen. Medical physicists have traditionally dealt with this motion by shooting a beam that broadly covers the area in which the tumor is located. Because there will be plenty of healthy tissue inside this big margin of error, the beam strength has to be turned down low.
A better way to treat cancer is to use intense, highly-focused beams that only strike the tumor. This is why the next generation of radiation treatments have robotic arms or special shutters that can move the beam up and down to stay centered on a moving target. But these new techniques will require a precise way to track where the tumor is inside the chest.
Nadeem Riaz and collaborators at Stanford University School of Medicine have a model that accurately predicts a tumor's motion using its last eight positions. The algorithm, which improves its performance by learning from its mistakes, is also used by the post office to automatically read zip codes on letters. The researchers tested their program on data from a previous radiation treatment in which a tumor was tracked with X-ray images and found it worked better than another simple model at predicting where the tumor will be one second into the future. One second should be enough time, Riaz says, for newly-developed technologies to redirect their radiation beams.
For more information: www.aapm.org
Source: American Association of Physicists in Medicine