Clinical Evaluation On The Therapeutic Effect Of Gamma Knife Radiosurgery For Intracranial Meningiomas

Objective To evaluate the therapeutic effects of gamma knife radiosurgery for the treatment of intracranial meningiomas in terms of tumor growth control, incidence of complications and choice of dosage. To provide theoretical basis for rational application of gamma knife radiosurgery for meningiomas so as to improve its clinical effectiveness and reduce complications.Methods Based on the completeness of imaging records, 83 patients were selected for the present study who were diagnosed as meningiomas and treated with gamma knife (GK) radiosurgery from October 1997 to December 2001. Of the 83 patients included in the study, 29 were males, 54 were females, and their mean age was 52±14 years old (range 6 ~ 80 years old). 28 patients received GK radiosurgery treatment for residual tumors after surgical removal of tumors and histological verification, while 54 patients with no prior surgical history received radiosurgery based on diagnosis by magnetic resonance imaging and computed tomography.A total of 87 meningiomas (4 of the 83 patients have multiple meningiomas) were found to be located in various brain regions: in the falcine and parasagittal (23 cases ,26.4%), sellar (14 cases , 16.1%), cerebellopontine angle (10 cases , 11.5%) , convexity ( 9 cases , 10.3%), sphenoid ridge (9 cases , 10.3%) , olfactory groove (5 cases , 5.7%) ,cavernous sinus(5 cases , 5.7%) ,tentorium(4 cases , 4.6%), intraventricular (4 cases , 4.6%) , orbital(2 cases , 2.3%) and posterior fossa (2 cases , 2.3%). The mean tumor volume, thereby calculated prior to GK radiosurgery, was 15.9 cm3 (range, 0.8-49.7 cm3). Depending on tumor location or sensitivity of surrounding brain tissues, 35% ~ 50 % of the isodose lines were chosen for radiosurgery. The maximal (central) dose ranged from 20 to 40 Gy (mean 30.7 Gy), while the marginal (peripheral) dose ranged from 10 to 20 Gy (mean 13.3 Gy). The selected doses were delivered with isocenters from one to fourteen.Changes in tumor volume were evaluated after at least one year of GK radiosurgery. The maximal tumor diameters measured from the same section layer were compared before and after radiosurgery. Tumor shrinkage was defined as greater than 2 mm reduction in tumor diameter post radiosurgery. A greater than 2 mm increase in diameter post radiosurgery was defined as tumor enlargement. Changes less than 2 mm in diameter were defined as tumor stabilization. Tumors were considered responsive to radiosurgery if they were categorized as either tumor clearance, tumor shrinkage or tumor stabilization. The tumor growth control (TGC) rate was calculated as the percentage of responsive tumors with respect to total tumors according to the formula: Responsive tumors (clearance + shrinkage + stabilization)/Total tumors *100%.Chi-square test was employed for correlation analysis of tumor growth control rate with tumor volume, marginal dose, age or pre-surgical history. The marginal doses were further analyzed with respect to incidence of complications and tumor locations.Results: 14~78 months (mean follow-up period: 32.8 months) after the GK radiosurgery, tumor clearance was noted in 25 patients (30.1%) , tumor shrinkage in 42 patients (50.6%), tumor stabilization in 6 patients (7.2%), and enlargement in 10 patient (12.1%). The tumor growth control (TGC) rate was 88%. Statistical analysis indicates that the tumor growth control rate significantly correlates with tumor volume (p =0.000< 0.05) at the time of treatment, but not with age, marginal dose, or surgical history. Incidence of complications such as brain edema occurs more frequently with tumors located in certain brain regions as in convexity, falcine and parasagittal. Marginal doses ranging 12 ~ 15 Gy were sufficient to control tumor growth with no increase in complications.Conclusions Gamma knife radiosurgery is effective for the treatment of small meningiomas (volume < 30cm3). As for large tumors (volume > 30cm3), gamma knife radiosurgery is beneficial for residual tumors after tumorectomy by surgery. Tumors located in certain brain regions, as in convexity, falcine and parasagittal, have high incidence of developing brain edema after radiosurgery. Therefore, radiosurgery for these patients should be recommended with caution. In addition, further investigations are needed for using marginal doses of radiosurgery in the treatment of meningiomas.