News | July 28, 2008

New Radiation Therapy Offers Shorter Treatment Time

July 29, 2008 - Intensity modulated radiation therapy (IMRT) is a method of depositing radiation with varying intensities to different parts of cancerous tumors, while sparing the surrounding healthy tissue from excessive exposure.

A new variant of IMRT, called volumetric modulated arc therapy (VMAT), promises further benefit to patients by offering the same treatment in half the time.

In the IMRT method, a computer-controlled linear accelerator sweeps a narrow (1-2 cm wide) slit of radiation across the tumor from five to nine angles around the patient, one angle at a time. The VMAT method, in contrast, delivers radiation in a 360-degree arc while the beam aperture shape continuously changes. A variant of the VMAT technique, proposed by Pengpeng Zhang, an assistant attending physicist at the Memorial Sloan-Kettering Cancer Center, and his colleagues Laura Happersett and Gig Mageras, breaks the arc into 360 evenly divided beams. A computer program developed by the researchers adjusts the aperture shape and radiation dose of each beam to maximize the radiation to the tumor while keeping healthy tissue exposure down at acceptable levels. Because the resulting beam apertures are much larger in VMAT than in IMRT, treatment time is substantially less and patient exposure to radiation leakage from the accelerator is reduced.

Zhang and his colleagues retrospectively evaluated the feasibility of this procedure in data from five patients treated for prostate cancer.

The treatment times they calculated were reduced by up to 50 percent - from the 5 minutes typical for IMRT down to 2 ½ minutes - with a corresponding decrease in the amount of radiation leakage received by healthy tissues. Zhang hopes to extend the technique to the treatment of other cancers, including those of the head and neck, brain and pelvis.

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Source: American Association of Physicists in Medicine