BOSTONBy reducing radiation to the parotid glands,
intensity modulated radiation therapy (IMRT) allows head and neck cancer
patients to maintain more saliva flow after therapy. Clifford K.S. Chao, MD, of
Washington University School of Medicine, St. Louis, reported the study results
at the 42nd Annual Meeting of the American Society for Therapeutic Radiology
The researchers assessed 41 patients treated with inverse
planning IMRT or forward-planning 3D radiation therapy between 1997 and 1999.
Only patients who received more than 50 Gy of radiation to the submandibular
glands were eligible for the study.
Saliva flow at 6 weeks, 3 months, and 6 months after therapy
was compared with pretreatment levels, and patients completed five
questionnaires about quality of life regarding oral comfort and eating and
At 6 months, measurement of more saliva flow correlated with
patient reports of greater ease in speaking and eating, said Dr. Chao,
assistant professor of radiology and chief of the Head and Neck Service at the
University’s Radiation Oncology Center.
"Dry mouth declined very substantially with IMRT, compared
with conventional treatment. In conventional beam radiation, two thirds of
patients still have xerostomia after a year," Dr. Chao told ONI in an
The condition is an important quality-of-life issue because
severe dry mouth can compromise eating and drinking functions. "It can
change social behavior and patterns," Dr. Chao said. "Some patients
won’t go out to eat with people."
The condition occurs when radiation aimed at head and neck
tumors reaches nearby parotid gland lobes, which are located below the ear. The
Washington University investigators used IMRT to sculpt radiation beams to
concentrate radiation on the tumor and reduce dose volume to the surrounding
tissues (see Figure). To avoid underdosing tumor targets in the parapharyngeal
space, the researchers attempted to spare only the superficial lobes of the
parotid glands. They re-contoured the entire parotid volume, however, to
compute dose-volume histograms for their analysis.
The investigators also developed a model to examine whether
functional outcome is related to radiation dose. This model showed an
exponential relationship between saliva reduction and the mean radiation dose
to the parotid glands (4% reduction in saliva flow per Gy of radiation to the
According to this model, about half of the baseline saliva flow
can be maintained if the mean dose to both parotid glands is less than 16 Gy,
Dr. Chao concluded. With a mean dose of 32 Gy, he said, a patient would have
about one fourth the pretreatment value of saliva flowequivalent to grade 4
Dr. Chao’s group has been investigating IMRT for about 4
years and has treated about 200 patients with various head and neck cancers.
Based on results so far, he predicts IMRT will be the cancer treatment of the
future. "The new technique provides dosimetric advantages and improves
treatment outcomes," he said.