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Stereotactic RT Controls Localized, Low-Grade Gliomas

Stereotactic RT Controls Localized, Low-Grade Gliomas

SALT LAKE CITY—When surgery and chemotherapy have failed, stereotactic
radiation therapy (RT) provides good local control of small, low-grade gliomas
in children for many years, Karen J. Marcus, MD, said at the American Society
for Therapeutic Radiology and Oncology 45th Annual Meeting (abstract 120). In
the prospective trial, about two thirds of children in whom surgery or
chemotherapy had not controlled the disease were alive with no progression 8
years after stereotactic RT.

"The management of low-grade gliomas in children remains controversial, and
there are a number of factors that influence treatment, including tumor
location, presence of neurofibromatosis, and age of the patient," said Dr.
Marcus, assistant professor of radiation oncology (pediatrics), Harvard Medical
School.

Dr. Marcus and her colleagues monitored outcomes in 50 children (median age,
9 years) who had localized, low-grade astrocytomas (including optic gliomas)
measuring no more than 5 cm and who were treated with stereotactic radiation
therapy between 1992 and 1998. The indications for stereotactic radiation
therapy were progression after subtotal resection or biopsy (38 patients) and
progression after chemotherapy (12 patients).

A 6-MV linear accelerator was used to deliver the radiation. The patients’
heads were positioned with two types of non-invasive relocatable head-frames, a
TLC frame for children requiring general anesthesia and the Gill-Thomson-Cosman
frame for older children, Dr. Marcus said. In planning the radiation therapy,
the investigators fused CT and MRI images to determine the tumor extent, used
the preoperative volume as the clinical target volume, and added a 2-mm margin.
The patients received a mean total radiation dose of 52.2 Gy (range, 50.4 to 58
Gy) in daily fractions of 1.8 Gy.

Outcomes were assessed over a median follow-up of 7 years (range, 1 to 10
years). Progression-free survival was about 83% at 5 years and 65% at 8 years
(Figure 1) and 98% and 82%, respectively, for overall survival (Figure 2).

Six patients had local progression between 15 and 92 months after radiation
therapy; in two of these patients, progression was to anaplastic astrocytoma at
3 and 7 years, respectively. "All progressions were within the primary tumor
bed, and all patients had received the full prescription dose. There were no
failures at or adjacent to the margin," she noted.

Five patients had CNS dissemination of their disease about 1 to 7 years
after their radiation therapy; all of these patients had primary
hypothalamic/optic system tumors. Two of these five patients remain alive with
stable disease, she said.

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