Low-grade astrocytomas: treatment with unconventionally fractionated external beam stereotactic radiation therapy.

Abstract

Fourteen patients with nonoperable low-grade astrocytomas were treated with unconventionally fractionated stereotactic radiation therapy. The target volume was defined with computed tomography (CT) performed under stereotactic conditions. The treatment was carried out with a technique producing multiple noncoplanar arc irradiation, with the center of the target volume placed at the isocenter of the linear accelerator. A total dose of 16-50 Gy was administered in either one fraction or two fractions 8 days apart. The concentration of dose within the target volume allowed reduction of dose absorbed by adjacent critical structures of the intact brain. Patients were followed up for 11-48 months. Twelve of 14 patients had a partial or complete response to treatment, as demonstrated by CT. Stereotactic radiation therapy appears to be effective in the control of small radioresistant cerebral neoplasms, without damaging surrounding healthy tissues.

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

“…Post treatment MRIs were recommended at 3-month intervals after the conclusion of therapy. The majority of patients (25) had their first post SRT MRI scan within 4 months, the remaining 3 at 5 , 6, or 9 months after completion of treatrnent (Patients 19, 20, 3). Fifteen patients (54%) had a reduction in tumor size including a decrease of ?50% over 9 to 20 months (9, 10, 12, 15, 15, 20 mos) in 6, and of 25 to 50% over 5 to 15 months (5, 6, 12, 13, 15 mos) in 5.…”

“…This protocol was approved by the Human Protection Committee and each patient gave informed consent. Eligibility criteria for low grade ;istrocytonia/pilocytic astrocytoma included: (1) biopsy-proven brain tumor, or presumed optic glioma in patients with NF 1 and an optic system tumor; (2) age 18 months to 25 years at time of enrollment; (3) evidence of progressive or symptomatic disease (16 patients), recurrence after surgery alone (9 patients), or after surgeiy plus chemotherapy (3 patients); and (4) no prior radiation therapy to the site. One patient had received prior irradiation, she had an optic glioma which had been irradiated with conventional techniques 9 years prior to treatment with SRT of a posterior medullary low grade astrocytoma.…”

Stereotactic Radiation in Primary Brain Tumors in Children and Adolescents

“…In adults with previously irradiated brain tumors (RTOG protocol 9005), Shaw et al [21]demonstrated that the maximum safe dose of a single fraction was 24 Gy for tumors smaller than 20 mm, 21 Gy for tumors measuring 21–30 mm, and 15 Gy for tumors 31–40 mm. Pozza et al [22]reported a 21.5% incidence of side effects in 14 patients with low-grade astrocytomas treated by SEBI therapy, especially when the field size was greater than 20 mm. For neurinomas, McKenzie et al [23]quoted Flickinger et al [18]who also found a relationship between tumor size and complication rate, and Noren et al [24]cautioned against treating tumors greater than 30 mm in diameter.…”

Clinical Applications of Stereotactic Radiosurgery

“…This approach is currently under investigation for the treatment. of selected malignant tumors [9,99]. It remains uncertain, however, whether this strategy would favorably or unfavorably alter the therapeutic ratio in the treatment of AVMs, where the target tissue consists of abnormal vascular shunts rather than neop~astic cells.…”

“…It was concluded that conventional fractionation schedules were preferable to radiosurgery. Some recent reports have described the use of multiply-fractionated stereotactic irradiation for the treatment of malignant brain tumors [9,99]. The theoretical considerations underlying this promising approach are discussed below (see Section on Future Directions).…”