v4n4 - Cancer's Molecular Machinery

The goal of radiation therapy is to irradiate as many cancer cells as possible while sparing normal, healthy cells. Improvements in radiation therapy include targeting specific tumor sites and counteracting involuntary movements, such as breathing, that make it difficult to zero in on a specific location, such as lung tumors.

Intensity-modulated radiation therapy (IMRT) uses multiple beams of radiation instead of a single high-dose beam, which can damage healthy tissue surrounding the tumor. While many IMRT devices use three-dimensional images, such as in computed tomography, newer devices include the aspect of time (4D IMRT). This form of image-guided radiation therapy localizes the target during each treatment to account for real-time organ motion. Because the location of the tumor can change with the patient’s breathing or other small movements, taking several images over time can help the radiologist pinpoint when and where the tumor is located during treatment.

In stereotactic radiosurgery, several weak beams of radiation originating from different angles intersect to produce a concentrated high dose of radiation at the tumor site. The procedure involves no surgery and little radiation to the surrounding tissue. CyberKnife® and Gamma Knife® use stereotactic radiosurgery to treat brain tumors (see page 39).

For breast cancer, partial breast irradiation employs radiation therapy within the lumpectomy cavity. It reduces side effects and cuts treatment time from six weeks to one week. With MammoSite®, a balloon filled with saline is placed inside the breast and a radioactive “seed” is delivered to the lumpectomy site. Other forms of brachytherapy, or radiation given internally, allow radiation to be given near or at the tumor site and radiated outward via radioactive seeds, wires or needles. Internal radiation techniques are used to treat breast, head and neck, gynecological and prostate cancers, among others.