High-Signal Intensity in the Dentate Nucleus and Globus Pallidus on Unenhanced T1-Weighted Images: Evaluation of the Macrocyclic Gadolinium-Based Contrast Agent Gadobutrol.

OBJECTIVE: The aim of this study was to compare changes in the signal intensity (SI) ratio of the dentate nucleus (DN) to the pons, DN to cerebrospinal fluid (CSF), and globus pallidus (GP) to thalamus on unenhanced T1-weighted magnetic resonance imaging (MRI) scans after serial injections of the macrocyclic gadolinium-based contrast agent gadobutrol. MATERIALS AND METHODS: Thirty patients who had received at least 5 MRI examinations (plus an additional last MRI for reference) with the exclusive use of gadobutrol, resulting in a total cumulative dose of 54.1 ± 30.4 mL gadobutrol, were analyzed retrospectively. Signal intensity ratio differences were calculated for DN-to-pons, DN-to-CSF, and GP-to-thalamus ratios by subtracting the SI ratio at the first MRI from the SI ratio at the last MRI scan. One-sample t tests were employed to examine if they differed from 0. Regression and correlational analyses were performed to examine whether the SI ratio differences were predicted by a number of control variables. RESULTS: Signal intensity ratio differences did not differ significantly from 0, neither for the DN-to-pons ratio (-0.0035 ± 0.0476, P = 0.69), the DN-to-CSF ratio (-0.0539 ± 0.3217, P = 0.37), nor the GP-to-thalamus ratio (-0.0020 ± 0.0211, P = 0.60). None of the control variables predicted changes in SI ratios. CONCLUSIONS: In contrast to a recently published study, we did not find signal increases in the DN or in the GP after serial injections of gadobutrol, even though the total dose applied here was considerably larger than in the respective study. This finding adds further support to the hypothesis that the molecular structure of a gadolinium-based contrast agent as either macrocyclic or linear is a crucial factor for its potential to cause gadolinium deposition in the brain. Future studies should further assess this hypothesis by additional animal investigations as well as histopathological and clinical correlation studies.

Low-dose rate stereotactic iodine-125 brachytherapy for the treatment of inoperable primary and recurrent glioblastoma: single-center experience with 201 cases.

Treatment options for inoperable glioblastoma are limited. Low-dose-rate stereotactic iodine-125 brachytherapy (SBT) has been reported as an effective and low-risk treatment option for circumscribed low-grade gliomas and brain metastases. The present study evaluates this treatment approach for patients with inoperable glioblastoma. Between 1990 and 2012, 201 patients with histologically proven glioblastoma were treated with SBT (iodine-125 seeds; median cumulative surface dose, 60 Gy; median dose-rate, 6 cGy/h; median gross-tumor-volume, 17 ml) either as primary treatment (n = 103) or at recurrence (n = 98). In addition to SBT, 90.3 % of patients in the primary treatment group received external boost radiotherapy (median dose, 25.2 Gy). Adjuvant chemotherapy was added for 30.8 % of patients following SBT and consisted of temozolomide for the majority of cases (88.7 %). Procedure-related complications, clinical outcome, progression-free and overall survival (PFS, OS) were evaluated. Median follow-up was 9.8 months. The procedure-related mortality was zero. During follow-up, transient and permanent procedure-related morbidity was observed in 7.5 and 2.0 %, respectively. Calculated from the time of SBT, median OS and PFS rates were 10.5 and 6.2 months, with no significant differences among primary and recurrent tumors (11.1 vs.10.4 months for OS and 6.2 vs. 5.9 months for PFS). For OS, multivariate analysis revealed Karnofsky performance score, age, and adjuvant chemotherapy as independent prognostic factors (all p < 0.01). Low-dose-rate SBT is a relatively safe and potentially effective local treatment option for patients with circumscribed inoperable glioblastoma initially or at recurrence. It deserves prospective validation since it may improve the outcome for a subset of patients with inoperable GBM.

Stereotactic iodine-125 brachytherapy for brain tumors: temporary versus permanent implantation.

Stereotactic brachytherapy (SBT) has been described in several publications as an effective, minimal invasive and safe highly focal treatment option in selected patients with well circumscribed brain tumors <4 cm. However, a still ongoing discussion about indications and technique is hindering the definition of a clear legitimation of SBT in modern brain tumor treatment. These controversies encompass the question of how intense the irradiation should be delivered into the target volume (dose rate). For instance, reports about the use of high does rate (HDR) implantation schemes (>40 cGy/h) in combination with adjuvant external beam radiation and/or chemotherapy for the treatment of malignant gliomas and metastases resulted in increased rates of radiation induced adverse tissue changes requiring surgical intervention. Vice versa, such effects have been only minimally observed in numerous studies applying low dose rate (LDR) regiments (3-8 cGy/h) for low grade gliomas, metastases and other rare indications. Besides these observations, there are, however, no data available directly comparing the long term incidences of tissue changes after HDR and LDR and there is, furthermore, no evidence regarding a difference between temporary or permanent LDR implantation schemes. Thus, recommendations for effective and safe implantation schemes have to be investigated and compared in future studies.