Radiosurgery/stereotactic radiotherapy in the therapeutical concept for skull base meningiomas

Microsurgical resection is still the treatment of choice for skull base meningiomas. But the risk of postoperative neurological deficits is high, and in many of these cases complete tumor removal cannot be achieved. Therefore recurrences are even more probable. Stereotactically guided radiation therapy - radiosurgery (RS) or stereotactic radiotherapy (SRT) - offers an additional or alternate treatment option for those patients. We evaluated local control rates, symptomatology, and toxicity.

224 patients were treated with stereotactically guided radiation techniques in two departments between 1997 and 2003. 129 of 224 had recurrences after 1 to 3 prior tumor resections and 95 of 224 were treated with SRT/RS alone. 87.9% of cases had benign, 7.8% had atypical and 4.3% had malignant meningiomas. RS was only applied in 11 cases. Tumor volumes ranged from 0.16 ccm to 3.56 ccm. The other 213 patients had larger tumor volumes of up to 135 ccm or a meningioma close to optical structures. Therefore 183 cases were treated with SRT in normal fractions of 1.8-2 Gy in single doses up to 60 Gy. Hypofractionated SRT with single fraction doses of 5 or 4 Gy was applied in 30 cases. Follow-up data were available in 181 skull base meningiomas and the progression-free and overall survival rates, the toxicity and symptomatology were evaluated.

The median follow-up was 36 months. The overall survival and the progression-free survival rates for 5 years were 92.9%, and 96.9%, respectively. Two tumor progressions have occurred to date but further follow up is required. Tumor volumes (TV) had shrunk about by 19.7% at 6 months (p<0.0001) and by 23.2% at 12 months (p<0.01) after SRT/RS. In 95.6% the symptoms had improved or were stable. Clinically significant acute toxicity (grade III) was seen in only 1 case (2.7%). Some patients developed late toxicity: 8.8% had grade I, 4.4% had grade II and 1.1% had grade III. No other neurological deficits occurred during follow-up.

SRT and RS offer an additional or alternative treatment option with a high efficacy and few side effects for the tumor control of skull base meningiomas. An individual and interdisciplinary decision respecting treatment is needed for each patient. In cases of large TV (>4 ccm), tumors adjacent to critical structures (<2 mm) or in high-risk patients the use of SRT offers greater benefits.