Doses of IMRT for prostate cancer vary widely among institutions

Substantial variation in the prescribed and delivered doses of intensity-modulated radiation therapy for prostate and other cancers exists among medical institutions, raising concerns about the validity of comparing clinical outcomes, according to a University of Pennsylvania study published in the Journal of the National Cancer Institute (2008; 100:300-7).

The retrospective analysis involved 803 patients treated with IMRT between October 2004 and July 2006 for brain, head and neck, or prostate cancer at five medical institutions that used different treatment planning systems. A prescribed dose to the target volume was extracted for each patient. The planned dose that was delivered to the patient was acquired from each treatment planning system. Actual minimum, maximum, median, and isocenter doses to the target volume were normalized to the prescribed dose and analyzed for each disease site and institution.

Of the 803 patients, 62% were treated for prostate cancer. The recorded dose variability from prescription was widespread for the minimum, maximum, and isocenter doses. A total of 46% of patients received a maximum dose that was more than 10% higher than the prescribed dose, and 63% of patients received a dose that was more than 10% lower than the prescribed dose.

At all five institutions, the prostate cancer cases had the smallest dosimetric variation, and the head and neck cancer cases had the largest variation. The median dose to the target varied from the prescribed dose by ±2% in 68% of patients, by ±5% in 88% of patients, and by ±10% in 96% of patients.

The recorded isocenter dose varied from prescription for all disease sites, and often does not reflect the dose specified by a selected isodose line encompassing the target volume, suggesting the need for national and/or international guidelines for dose prescription, planning, and reporting for a meaningful clinical trial, according to the researchers, led by Indra J. Das, PhD.