Magnetic resonance imaging changes after stereotactic radiation therapy for childhood low grade astrocytoma.

BACKGROUND: Stereotactic radiotherapy (SRT) is fractionated radiotherapy delivered under stereotactic guidance to produce highly focal and precise therapy. We studied the incidence of imaging changes that can mimic tumor progression after completion of SRT for childhood low grade astrocytoma.
METHODS: Between June 1992 and September 1994, we prospectively treated 28 children with low grade astrocytomas with SRT. The patients ranged in age from 2 to 22 years (median: 10 yrs) and none had received prior radiation therapy or radiosurgery. Routine fractionation was employed (180-200 centigray[cGy]) to a total dose of 5220-6000 cGy over 5 to 6 weeks. All of the patients underwent initial and follow-up magnetic resonance imaging (MRI) according to protocol.
RESULTS: Median clinical follow-up for the 28 patients was 24 months (range, 5-32 mos) with a median radiographic follow-up of 15 months (range, 3-26 mos). Fifteen patients had reduction in tumor size, one patient had stable disease. Twelve patients (43%) developed increased size of the lesion, increased signal intensity or enhancement, cysts or cavitations, and an increase in edema or mass effect on follow-up MRI. Most of these changes occurred between 9 and 12 months after the start of SRT and resolved or decreased by 15 to 21 months. All but one patient had normal or stable neurologic examinations.
CONCLUSIONS: Treatment-related MRI changes are common after conventionally fractionated schedules using stereotactic radiation techniques for patients with low grade astrocytomas. These changes can be distinguished from tumor progression by their transient nature as well as the general absence of clinical symptoms.