Image fusion analysis of volumetric changes after interstitial low-dose-rate iodine-125 irradiation of supratentorial low-grade gliomas

Value of CT-MRI fusion in iodine-125 brachytherapy for high-grade glioma

Purposes

To develop a fast, accurate and robust method of fusing Computed Tomography (CT) with pre-operative Magnetic Resonance Imaging (MRI) and evaluate the impact of using the fused data on the implantation of Iodine-125 (¹²⁵I) seeds for brachytherapy of high-grade gliomas (HGG).

Methods

A study was performed on a cohort of 10 consecutive patients with HGG were treated by ¹²⁵I brachytherapy with CT-MRI fusion image guided (CMGB), and 10 patients treated with CT alone guided (CGB). Statistical analysis was performed to compare (1) the planning target volume, (2) the accuracy of location of catheters, (3) the target volume covered by 150% prescribe dose (V150), (4) the target volume covered by 200% prescribe dose (V200), and (5) the conformity index (CI) with or without fused data.

Results

The median planning target volume was 50.1 cm³ in CGB, and 56.25 cm³ in CMGB with significant difference (p = 0.005). The accuracy of catheter insertion was 94.4% with CMGB and 78.9% with CGB. The median V150 and V200 was 45.32% vs 64.24% and 32.81% vs 53.17% in CGB and CMGB, respectively. There was significant difference for CI (83.5% vs. 74.5%, p < 0.05) in the two groups for the post-operative verification.

Conclusions

The proposed MRI-CT fusion method enables a quantitative assessment of impact on HGG brachytherapy. The additional information obtained from the fused images can be utilized for more accurate delineation of lesion boundaries and targeting of catheters. Experimental results show that the fusion algorithm is robust and reliable in clinical practice.

Imaging after GliaSite brachytherapy: prognostic MRI indicators of disease control and recurrence

PURPOSE

In this study, we analyzed the magnetic resonance imaging (MRI) changes in patients after GliaSite treatment and characterized the prognostic MRI indicators in these patients.

METHODS AND MATERIALS

A total of 25 patients with recurrent glioblastoma multiforme were treated with the GliaSite Radiation Therapy System. Patients at the Johns Hopkins Hospital with recurrent glioblastoma multiforme underwent surgical resection followed by GliaSite balloon implantation. Available MRI scans for 20 patients were obtained throughout the post-GliaSite treatment course. These were reviewed and analyzed for prognostic significance.

RESULTS

After GliaSite treatment, all patients developed some degree of T(1)-weighted contrast and T(2)-weighted hyperintensity around the resection cavity. The development of enhancement on T(1)-weighted contrast-enhanced imaging and the size of these lesions, in the absence of increasing T(2)-weighted hyperintensity, before clinical progression was not associated with decreased survival. Patients with T(1)-weighted enhancement >1 cm had a median survival of 13.6 months and those with T(1)-weighted lesions <or=1 cm had a median survival of 8.5 months (p = .014). In contrast, the development of larger areas of T(2)-weighted hyperintensity surrounding the resection cavity was significantly associated with poorer survival (p = .027).

CONCLUSION

After GliaSite treatment, characteristic T(1)- and T(2)-weighted changes are seen on MRI. Greater T(1)-weighted changes in the absence of increasing edema appears not to indicate disease progression; however, greater T(2)-weighted changes were associated with decreased survival. These findings suggest that T(1)-weighted enhancement in the absence of concomitant edema after GliaSite treatment might represent pseudoprogression. Conversely, increasing T(2)-weighted hyperintensity might reflect infiltrative disease progression. These results provide a framework for the analysis of disease control in future prospective studies of GliaSite treatment.

Prediction of volumetric change in the "triple ring" caused by glioma I-125 brachytherapy

The aim of this study was to reveal the volumetric changes in tumor necrosis, reactive zone, and edema referred to as the "triple ring" appearing after low-dose-rate iodine-125 (I-125) interstitial irradiation of 20 inoperable low-grade gliomas. To enable prediction of these volumetric changes, we provide mathematical expressions that describe the dynamics of the triple ring. Volumes of the three regions on image-fused control CT/MR images were measured for a 24-month period. The delivered dose on the tumor surface was 50-60 Gy. Dose planning and image fusion were performed with Brain-Lab Target 1.19 software; mathematical and statistical computations were carried out with Matlab numeric computation and visualization software. To determine the volumes, control images with the triple rings were fused with the planning images. Relative volumes normalized with respect to the volume of reference dose were calculated and plotted in the time domain. First, the mean values of volumes were determined from the patients' measured data; then, polynomials were fitted to the mean values using the polynomial curve-fitting method. The accuracy of our results was verified by correlating the predicted data with the measured ones. The polynomial prediction approach proposed here reveals the dynamics of the triple ring. These polynomials will assist with (1) designing the best treatment, (2) following the patient's condition, and (3) planning reirradiation if necessary.