STEREOTAXIC RADIOTHERAPY FOR PEDIATRIC AND ADULT BRAIN-TUMORS - PRELIMINARY-REPORT

Purpose: Stereotactic radiotherapy is a new modality that combines the accurate focal dose delivery of stereotactic radiosurgery with the bi ological advantages of conventional radiotherapy (1.8-2.0 Gy/day using 25-30 fractions). The modality requires sophisticated treatment plann ing, dedicated high-energy linear accelerator, and relocatable immobil ization devices. We report here our early experience using stereotacti c radiotherapy for intracranial neoplasms. Methods and Materials: Betw een June 1992 and September 1993, we treated 82 patients with central nervous system lesions using stereotactic radiotherapy, delivered from a dedicated 6 MV stereotactic linear accelerator. A head fixation fra me provided daily relocatable setup using a dental plate for all patie nts over 8 years of age. A modified head frame, which does not require a mouthpiece, was used for children requiring anesthesia. The patient s ranged in age from 9 months to 76 years. Thirty-three patients were children less than 21 Sears of age. Selection criteria for the protoco l included: (a) focal, small(<5 cm) radiographically distinct lesions known to be radiocurable (pituitary adenoma, craniopharyngioma, mening ioma, acoustic neuroma, pilocytic astrocytoma, retinoblastoma), and (b ) lesions located in regions not amenable to surgery or radiosurgery s uch as the brain stem or chiasm. Standard fractionation and convention al doses were delivered. Patients with low-grade astrocytoma, oligoden droglioma, or ependymoma were treated using a dose escalation regime c onsisting of conventional doses plus a 10% increase. Results: Although follow-up is 16 months (range 3-16 months), posttreatment radiographi c studies in 77 patients have been Consistent with changes similar to those found after conventional radiation therapy. To date, reduction o f up to 50% of the original volume has been noted in 19 out of 77 pati ents, and 4 patients had a complete response, 2 with dysgerminoma, and 1 each with astrocytoma and retinoblastoma. In 56 patients disease wa s either stable or the follow-up was too short for evaluation. While t he follow-up is relatively short, there have been no in-field or margi nal recurrences. The only unexpected radiographic findings were in thr ee patients with pilocytic astrocytomas, who developed asymptomatic ed ema in the treatment volume. Accuracy in daily fractionation was excel lent. In over 2000 patient setups with 41,000 scalp measurements, repr oducibility was found to be within 0.41 mm (median) of baseline readin gs, allowing for precise immobilization throughout the treatment cours e. The treatment in all cases was well tolerated with minimal acute ef fects. Our stereotactic radiotherapy facility can provide fractionated therapy for 10-12 patients a day efficiently and accurately. Conclusi ons: The treatment and relocatable stereotactic head frames were well tolerated with minimal acute effects. No long-term sequelae have been noted, although the observation period is short. To fully define the r ole of stereotactic radiotherapy, we are conducting prospective studie s to evaluate neurocognitive and neuroendocrine effects. We expect tha t this innovative approach will make a significant impact on the treat ment of intracranial neoplasms, particularly in children.