Quantitative analysis of tumor volume reduction after three-dimensional conformal radiation therapy for intracranial meningiomas.

To provide radiobiological information on the inherent response of intracranial meningiomas after three-dimensional conformal radiation therapy. Quantitative tumor volume measurements were generated from 120 magnetic resonance images of a total of 24 patients. Gross tumor volumes were delineated on a series of contrast-enhanced T1-weighted magnetic resonance images by using commercial software. The percentage of tumor volume reduction at each follow-up was determined and compared to the baseline tumor volume. The median follow-up time was 103.5 months (range 30-137 months). The mean pre-radiation therapy tumor volume was 30.0 cm(3) (range 1.3-167.4 cm(3)). Tumor volume reduction was observed in 96 % of the study population. The mean absolute and relative tumor volume reduction were 14.0 cm(3) (range -0.6-84.5 cm(3)) and 40.8 % (range -6.8-82.9 %), respectively. The mean relative tumor volume reduction was 15.9, 28.9, 40.5, 50.3, and 52.6 % at 2, 4, 6, 8, and 10 years after irradiation. The quantitative volumetric analysis of the pattern of tumor volume reduction in response to irradiation gives an insight into the radiobiological nature of intracranial meningiomas after conventionally fractionated radiation therapy.