Radiation-induced microbleeds after cranial irradiation: evaluation by phase-sensitive magnetic resonance imaging with 3.0 tesla

Abstract

Background: Although there are many reports regarding radiation-induced microbleeds, its frequency, relation to dose and latency after radiation are not fully elucidated. The purpose of this study was to evaluate the frequency, latency, patient factors and dose relation of radiation-induced microbleeds after cranial irradiation using phase-sensitive magnetic resonance imaging (PSI) at 3.0 T.

Methods: Retrospective evaluation of 34 patients (age range, 13-78 years; mean, 49 years; follow-up period, 3-169 months; mean 29 months) who had undergone cranial irradiation using magnetic resonance (MR) imaging including PSI was performed. Twenty-three patients received high-dose irradiation (44-60 Gy), and 11 patients received 24-30 Gy whole brain irradiation. When microbleeds were detected on MR imaging in these high-dose irradiation patients, dose distribution maps were reproduced by reviewing the clinical records. Then the irradiated areas were divided into 6 radiation-dose classes: regions > 55 Gy, 45-55 Gy, 35-45 Gy, 25-35 Gy, 15-25 Gy and 5-15 Gy. The frequency of microbleeds in each radiation-dose class was analyzed.

Results: Microbleeds were detected in 7 (21%) of 34 patients on T2-weighted imaging, whereas they were detected in 16 (47%) of the 34 patients on PSIs. The frequency of microbleeds was higher than previously reported. The latency of radiation-induced microbleeds after radiation was 3 months to 9 years (mean, 33 months). In high-dose irradiation patients, the frequency of microbleeds significantly was associated with radiation dose. There were no foci that were observed in regions that had received < 25 Gy.

Conclusion: Radiation-induced microbleeds occurred more frequently in the present study than has been previously reported. PSI can be used to detect these vascular changes earlier than other conventional MR imaging techniques.

Keywords: cranial irradiation; magnetic resonance imaging; radiation injury.

Fig. 1.

A 31-year-old man with surgical resection of a high-grade glioma in the left parietal lobe, which was followed by localized irradiation at a dose of 60 Gy. A: PSI obtained 17 months after completion of radiation therapy. B: PSI obtained 33 months after completion of radiation therapy. A hypointense focus that cannot be detected in A appears in the left parietal white matter in B (arrow). This focus can be interpreted as microbleed. C: T2-weighted image obtained 33 months after completion of radiation therapy. The microbleed detected in B cannot be detected. D: Fused PSI image. The microbleed is contoured. E: Reproduced dose distribution map. The microbleed is recognized in regions with > 55 Gy. PSI, phase-sensitive magnetic resonance imaging.