Intracranial meningeomas: Time- and dose-dependent effects of irradiation on tumor microcirculation monitored by dynamic MR imaging

Abstract

The purpose of this study was the characterization of the time- and dose-dependent effects of irradiation on tumor microcirculation by means of dynamic MR imaging and correlation of the estimated data with tumor response in patients with meningeomas. Dynamic MR imaging studies were performed in 20 patients with intracranial meningeomas prior to ( n = 20) and at 6 ( n = 17), 18 ( n = 17), and 50 wk ( n = 14) after the end of radiotherapy. In seven of these patients, dynamic measurements were also performed during fractionated radiotherapy after approximate 20 Gy and 54 Gy. During and after short-time infusion of gadopentetate dimeglumine, the kinetics of lesion response was resolved using a strongly T 1-weighted saturation recovery TurboFLASH (SRTF) sequence. The signal-time courses of the suspected lesions were analyzed using a pharmacokinetic two-compartment model. The calculated parameters amplitude A (reflecting gadopentetate dimeglumine accumulation in the extracellular space) and exchange rate constant k 21 (depending on vascular permeability and blood flow) were displayed as color-coded images and analyzed as a function of time of therapy and radiation dose. All meningeomas showed a high exchange rate constant k 21 (median, 5.7 min −1; range, 1.9–23.0 min −1) and a high amplitude A (median, 1.5 arbitrary units; range, 1.1–2.7) prior to X-ray treatment. During radiotherapy we found a dose related significant ( p < .01) increase of k 21 accompanied by an increase of the amplitude A as compared to the pretreatment values. Analysis of tumor volume 6, 18, and 50 wk after X-ray treatment revealed two different groups. In the responder group ( n = 13) the median of the tumor volume decreased from 10.0 to 7.5 cm 3. For this group, we found a significant drop ( p < .01) of the median of the amplitude A and a decrease of the exchange rate constant k 21. In the nonresponder group ( n = 4) the median of the tumor volume increased after radiation from 3.5 to 4.5 cm 3. The pharmacokinetic analysis revealed a decrease of the amplitude A and an increase of the exchange rate constant k 21. The response of meningeomas to radiotherapy is influenced by the effect of X-rays on tumor microcirculation. This effect on tumor microcirculation can be derived by analysis of pharmacokinetic maps obtained from dynamic MR images. Furthermore, these pharmacokinetic maps can possibly be used to differentiate groups of patients who respond or do not respond to radiotherapy and, thus, could benefit from another treatment modality.