Radiation-Induced Microbleeds after Cranial Irradiation: Evaluation by Phase-Sensitive Magnetic Resonance Imaging with 3.0 Tesla

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 thisstudy was to evaluate the frequency, latency, patient factors and dose relation ofradiation-induced microbleeds after cranial irradiation using phase-sensitive magneticresonance 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 irradiationusing magnetic resonance (MR) imaging including PSI was performed. Twenty-three patientsreceived high-dose irradiation (44–60 Gy), and 11 patients received 24–30 Gy whole brainirradiation. When microbleeds were detected on MR imaging in these high-dose irradiationpatients, 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 eachradiation-dose class was analyzed.

Results

Microbleeds were detected in 7 (21%) of 34 patients on T2-weighted imaging, whereasthey were detected in 16 (47%) of the 34 patients on PSIs. The frequency of microbleeds washigher than previously reported. The latency of radiation-induced microbleeds afterradiation was 3 months to 9 years (mean, 33 months). In high-dose irradiation patients, thefrequency of microbleeds significantly was associated with radiation dose. There were nofoci that were observed in regions that had received < 25 Gy.

Conclusion

Radiation-induced microbleeds occurred more frequently in the present study than has beenpreviously reported. PSI can be used to detect these vascular changes earlier than otherconventional MR imaging techniques.