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Refining Targets to Reduce Late-Appearing Radiation Side Effects in Head and Neck Cancer

Refining Targets to Reduce Late-Appearing Radiation Side Effects in Head and Neck Cancer

ST. LOUIS—Intensity modulated radiation therapy (IMRT) and use of
radioprotectant agents may help reduce late-appearing radiation side
effects, reported K. S. Clifford Chao, MD. Dr. Chao is associated radiation
oncologist, Department of Radiation Oncology at the Mallinckrodt Institute
of Radiology, Washington University School of Medicine, St. Louis.

Dr. Chao stressed the importance of refining the definition of the
radiation target. "The problem with target definition is that no one
has published any real guidelines for head and neck IMRT. Articles that talk
about the normal N0 neck, for example, point out the lymph nodes; in the
real IMRT case we see a less clear situation. If you want to do elective
neck radiation, some N0 tissue will be in the region to be treated. We need
to settle issues of how to treat such cases," Dr. Chao said.

The situation with postoperative patients is even more complex.
"Half of our patients are postop," Dr. Chao said. "How you
delineate the target is extremely important. If you draw the target all the
way to the skin, our experience is that it is unlikely that the patient will
finish the treatment without any break. The skin reaction is likely to be
very severe."

A related issue is how to determine the dose. "We prescribe the IMRT
dose with biological equivalent dose (BED) correction. The issues of
appropriate fraction size, toxicity, and whether at the lower end, 1.5 Gy is
enough for the low-risk region need to be addressed further," Dr. Chao

Locoregional Failure

Dr. Chao reported data from his institution on patterns of locoregional
failure after head and neck IMRT in 108 patients treated from 1997 to 2000,
with median follow-up of 27 months. Data for 21 of these patients were
excluded due to palliative repeat of radiotherapy or IMRT as boost. The 87
evaluable patients included 40 treated with definitive IMRT and 47 treated
with postoperative IMRT. Of the 40 who received definitive IMRT, 26 also
received cisplatin (Platinol)-based chemotherapy, and 14 were treated with
IMRT alone.

There were 12 locoregional failures. "The majority of local-regional
failures were within the high-dose region. We only see about 2.3% marginal
failures, but what’s important is that we don’t see failure right next
to the parotid gland. There has been concern in the community that sparing
the parotid gland would spare the tumor. We didn’t see that," Dr.
Chao said.


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