Data support need for IMRT dose prescription guidelines

Variability in dose prescription, planning and reporting exists among medical institutions.

Differences between the prescribed and actual doses of intensity-modulated radiation therapy have raised concerns about the comparison of clinical outcomes among medical institutions.

According to data from a recent study, 46% of patients received a maximum IMRT dose that was more than 10% higher than the prescribed dose. Sixty-three percent of patients received a dose that was more than 10% lower than the prescribed dose. The data were reported in the Journal of the National Cancer Institute.

Indra Das, PhD, a professor of radiation oncology in the division of medical physics at the University of Pennsylvania, suggested the need for national and/or international guidelines for IMRT dose prescription, planning and reporting.

“It’s difficult to compare outcomes unless we know precisely what the patients are receiving,” Das told HemOnc Today. “IMRT is a new modality that is not as exact as previous radiation modalities and produces significant dose variability.”

Variable doses

Das and colleagues conducted the retrospective analysis of 803 patients who were treated with IMRT between October 2004 and July 2006. The patients had been treated at one of five medical institutions. Sixty-two percent were treated for prostate cancer, 12% for brain cancer and 26% for head and neck cancer.

Patients with prostate cancer had the smallest dosimetric variation, whereas patients with head and neck cancer had the largest variation. The median dose 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 typical accepted dose variation is ±10%, but should be minimized to ±5%, according to the researchers.

According to Louis Harrison, MD, a HemOnc Today Editorial Board member, these data are a call to the radiation oncology community to make IMRT planning and delivery less variable.

“This is an important issue,” Harrison said in an interview. “If there were greater agreement in the radiation oncology community, it would be easier to compare outcomes among institutions and to make more progress toward improved outcomes.”

Call for guidelines

In an accompanying editorial, John Willins, PhD, and Lisa Kachnic, MD, both of the departments of radiation oncology at Boston Medical Center and Massachusetts General Hospital, wrote that this is valuable information for clinicians who take part in multicenter clinical trials. The variability is partially attributed to different IMRT planning software at different institutions.

They agree with the need for more uniformity in IMRT dose specification and reporting and with setting limits on an acceptable amount of radiation above the peak dose.

“Widespread use of IMRT planning standards 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,” they wrote. “At the same time, any standardization should be done in a way that prioritizes clinical utility and preserves flexibility for the practitioner to encourage acceptance.” – by Emily Shafer

For more information:

Das IJ, Cheng CW, Chopra K, et al. Intensity-modulated radiation therapy dose prescription, recording, and delivery: patterns of variability among institutions and treatment planning systems. J Natl Cancer Inst. 2008;100:300-307.

Willins J, Kachnic L. Clinically relevant standards for intensity-modulated radiation therapy dose prescription. J Natl Cancer Inst. 2008;100:288-290.