Evaluation of the response of metastatic brain tumors to stereotactic radiosurgery by proton magnetic resonance spectroscopy, 201TICI single-photon emission computerized tomography, and gadolinium-enhanced magnetic resonance imaging

Object. The goal of this study was to investigate the usefulness of proton (H-1) magnetic resonance (MR) spectroscopy to evaluate the response of metastatic brain tumors to stereotactic radiosurgery (SRS) in comparison with Gd-enhanced MR imaging and single-photon emission computerized tomography with administration of thallium-201 chloride ((TlCl)-Tl-201-SPECT). Methods. Forty patients with a total of 47 metastatic brain tumors were evaluated. The primary lesion was identified in all cases. Stereotactic radiosurgery was effective in 37 lesions. All patients were examined using Gd-enhanced MR imaging before and after SRS. Thalium-201 chloride was administered to 27 patients with 34 tumors and SPECT images were obtained. Proton MR spectroscopy was performed in 36 patients who harbored 43 tumors. On Gd-enhanced MR images, a decrease in the volume of the Gd-enhanced lesion and a change in the enhanced effect in the lesion after treatment were recognized as showing the effectiveness of SRS between I and 3 months or more (mean 8.54 +/- 3.58 weeks). In (TlCl)-Tl-201-SPECT studies, the ratio of lesion to normal brain decreased from 2 weeks to 2 months (mean 5.03 +/- 2.77 weeks) after radiosurgery. On H-1-MR spectroscopy images a high choline (Cho) peak and a lipid-dominant (Lip) peak were observed in 25 lesions and a high Cho peak and a lactate-dominant (Lac) peak were observed in 12 lesions before SRS. A decrease in the Cho peak, a disappearance of the Lac peak. and an increase in the Lip peak were observed between I week and I month (mean 2.76 +/- 1.62 weeks) after treatment. Conclusions. Based on histopathological findings obtained at autopsy or at surgery, we assume that a high Cho peak may be observed in viable tumor tissue and a Lip peak in areas of necrosis. The results indicate that H-1-MR spectroscopy is potentially a more sensitive tool in evaluating the response to SRS than (TlCl)-Tl-201-SPECT or Gd-enhanced MR imaging and that it can be used earlier for this purpose than those other imaging methods.