Guidelines for Dose Required

IMRT systems are designed to deliver the prescribed dose of radiation to a tumor while sparing surrounding tissues. IMRT does this by delivering many small beams of radiation that are individually controlled. Because of the complexity of the system, radiation oncologists and physicists rely on special software and equipment to deliver the planned dose over the treatment area.

In the current study, Indra J. Das, Ph.D., and colleagues at the University of Pennsylvania in Philadelphia reviewed the data for 803 patients who were treated with IMRT for brain, prostate, or head and neck cancer at one of five institutions between October 2004 and July 2006. The researchers determined the minimum, maximum, and median radiation doses delivered over the targeted region by using the planned dose for each patient and measuring the actual amount of radiation in plastic or water that radiologically resembles tissue.

By comparing the measured dose to the planned dose, the investigators discovered that 369 patients (46 percent) received a maximum dose delivered to some portion of the tissue that was more than 10 percent above the prescribed dose. Ten percent is the typically acceptable level of variation. Moreover, the minimum dose delivered to the tumor site in 506 patients (63 percent) was more than 10 percent below the prescribed dose.

“We found that in IMRT the prescribed dose rarely corresponded to the planned, or delivered, dose,” the authors write. “Dosimetric variations between the prescribed dose and the recorded dose could be reduced by establishing international and/or national guidelines.”; Source: Journal of the National Cancer Institute