Prescribed and delivered doses of intensity-modulated radiation therapy (IMRT) vary widely, researchers report in the Journal of the National Cancer Institute. In light of these findings, they call for standardization. Prescribed and delivered doses of intensity-modulated radiation therapy (IMRT) vary widely, researchers report in the March 5th issue of the Journal of the National Cancer Institute. In light of these findings, they call for standardization.

"With present IMRT practices," lead investigator Dr. Indra J. Das told Reuters Health, "cancer patients do not receive radiation doses that are as prescribed by the clinicians."

Dr. Das of the University of Pennsylvania Medical Center in Philadelphia and colleagues note that IMRT treatment planning software as well the particular machine involved influence dosage.

In their review of data on 803 patients who underwent IMRT for cancers of the brain, head and neck, or prostate at five different centers, the investigators found that 46 per cent of patients received a maximum dose more than ten per cent higher than the prescribed dose, and 63 per cent received a dose more than ten per cent lower.

Overall, the smallest dosimetric variations were in prostate cancer patients and the largest were in head and neck cancer patients.

The median dose to the target was two per cent higher or lower than the prescribed dose in 68 per cent of the patients, five per cent higher or lower in 88 per cent of the patients, and ten per cent higher or lower in 96 per cent.

"Patients treated in different centers do not get a standard and uniform dose in IMRT, which used to be the case in the era of conformal therapy," Dr. Das said. "The variability in radiation dose is huge and creates ambiguity in outcome from the clinical trials using IMRT."

In an accompanying editorial, Drs. John Willins and Lisa Kachnic of Boston Medical Center agree on the need for IMRT planning standards. Widespread use of such standards, they say, "would not only facilitate multicenter clinical trials but would also provide clinicians with solid guidance in their everyday practice on the question of what constitutes a 'good' IMRT plan.