MAGNETIC-RESONANCE-IMAGING CHANGES AFTER STEREOTAXIC RADIATION-THERAPY FOR CHILDHOOD LOW-GRADE ASTROCYTOMA

BACKGROUND. Stereotactic radiotherapy (SRT) is fractionated radiothera py delivered under stereotactic guidance to produce highly focal and p recise therapy. We studied the incidence of imaging changes that can m imic tumor progression after completion of SRT for childhood low grade astrocytoma. METHODS. Between lune 1992 and September 1994, we prospe ctively treated 28 children with low grade astrocytomas with SRT. The patients ranged in age from 2 to 22 years (median: 10 yrs) and none ha d received prior radiation therapy or radiosurgery. Routine fractionat ion was employed (180-200 centigray [cGy]) to a total dose of 5220-600 0 cGy over 5 to 6 weeks. All of the patients underwent initial and fol low-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, 3-2 6 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 cavitation s, and an increase in edema or mass effect on follow-up MRI. Most of t hese changes occurred between 9 and 12 months after the start of SRT a nd resolved or decreased by 15 to 21 months. All but one patient had n ormal or stable neurologic examinations. CONCLUSIONS. Treatment-relate d MRI changes are common after conventionally fractionated schedules u sing stereotactic radiation techniques for patients with low grade ast rocytomas. These changes can be distinguished from tumor progression b y their transient nature as well as the general absence of clinical sy mptoms. (C) 1996 American Cancer Society.