Intensity modulated radiotherapy in high grade gliomas: Clinical and dosimetric results

Abstract

1532 Background: Intensity Modulated Radiotherapy (IMRT) is an emerging treatment for brain tumors, but there is very little clinical or dosimetric data on doses and outcomes from IMRT treatment for malignant gliomas. This study reports the preliminary data with IMRT in these tumors. Methods: Sixty six consecutive high grade gliomas were treated between January 2001 and December 2003 with dynamic multileaf collimator IMRT with inverse planning. A dose of 59.4–60Gy using 1.8–2.0 Gy per fraction was delivered. 3–5 non-coplanar beams were used for the IMRT plan to cover at least 95% of the target volume with the prescription isodose line. Glioblastoma accounted for 62% of the cases and oligodendroglioma histology (pure or mixed) was seen in 16.7% of the cases. Surgery was restricted to biopsy only in 26% of the patients. 80% of the patients received adjuvant chemotherapy. Results: With a median follow-up of 18 months, 85% of the patients have relapsed. The median disease free survival for anaplastic glioma and glioblastoma were 5.6 and 2.5 months. The median overall survival for the anaplastic glioma and glioblastoma histologies were 16.5 and 10.6 months respectively. 96% of the recurrences were local. No grade IV delayed neurological toxicities were noted. A comparative dosimetric analysis revealed that regardless of tumor location, IMRT did not improve target coverage compared to conventional 3-dimensional treatment planning. However, the use of IMRT resulted in a decreased dose to spinal cord, optic chiasm and brain stem by 19%, 4.5% and 8% respectively due to its improved dose conformality. Use of IMRT did not result in an increase of the dose received by the normal brain. Conclusions: Use of IMRT did not increase either the disease free survival or the overall survival in patients with malignant gliomas when compared to historical controls. It is unlikely that IMRT will improve the local control in high grade gliomas without further dose escalation. However, it may result in decreased late toxicities associated with radiation therapy. No significant financial relationships to disclose.