ST. LOUISIntensity 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 said.
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(Drug information on 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.