Assessment of glioma response to radiotherapy using 3D pulsed-continuous arterial spin labeling and 3D segmented volume

Abstract

Background: Gliomas are the most common primary brain tumors in adults, in some cases, radiotherapy may be the preferred treatment option especially for elderly people who cannot endure surgery. Therefore, it is necessary to evaluate the effects of radiotherapy on glioma. Arterial spin labeling (ASL) is an MR imaging technique that allows for a quantitative determination of cerebral blood flow (CBF) noninvasively. Tumor volume is still an important determinant for evaluating treatment response. The purpose of this study was to investigate the relationship between the tumor perfusion parameters and tumor volume and assess the effects of radiotherapy on glioma using pulsed-continuous arterial spin labeling (pcASL) technique.

Methods: 35 patients with gliomas, histologically classified as low-grade group (n=16) and high-grade group (n=19), treated with radiotherapy only or before using other therapies were included in this study. MR examinations, including T1 weighted image and pcASL, were performed before and 4, 8, 12, 16 weeks after radiotherapy. Regional CBF of normal tissue, mean tumor blood flow (TBF_mean), maximum tumor blood flow (TBF_max), and tumor volume were evaluated at each time point. Both the percentage change in CBF (CBF ratio), TBF_mean (TBF_mean ratio), TBF_max (TBF_max ratio) and the percentage change in tumor volume (volume ratio) were calculated using values obtained before and after radiotherapy. The correlation between the volume ratio and CBF ratio, TBF_mean ratio, TBF_max ratio was assessed using linear regression analysis and Pearson's correlation.

Results: The TBF_mean and TBF_max of high-grade gliomas were significantly higher than that of low-grade group. In high-grade group, a strong correlation was demonstrated between the tumor volume and the TBF_max before radiotherapy (R²=0.35, r_s=0.59, p<0.05). There was also a significant correlation between the TBF_max before radiotherapy and the tumor volume ratio before and 8 weeks after radiotherapy (R²=0.56, r_s=-0.74, p<0.05).

Conclusion: The TBF_max measured using pcASL could assess tumoral grade and also could become a potential tool for evaluating the therapeutic effects of radiation.

Keywords: Cerebral blood flow (CBF); Gliomas; Pulsed-continuous arterial spin labeling (pcASL); Radiotherapy; Tumor blood flow (TBF).