The value of serial MR imaging in the assessment of brain metastases volume control during stereotactic radiosurgery

Purpose: To evaluate early tumour control capabilities of Stereotactic Radiosurgery (SRS) in the treatment of brain metastasis and the role of follow-up MR imaging. Methods and Materials: MR imaging of 54 metastases in 31 patients treated with SRS who underwent follow-up MR imaging within 12 months were retrospectively reviewed. Tumours were characterized as either enlarged (>20% volume increase), stable (follow-up volume ±20% of the initial volume), or decreased (> 0% volume decrease). Results: Within the first 6 weeks following SRS a decrease was observed in 25 (52%) of the tumours in the extent of 63% in size. Tumour reduction varied according to histopathological subtype with 38% of non-small cell lung carcinomas, 41% of breast carcinomas, 14% renal cell carcinoma and 8% of melanomas. At 9 weeks, 7 out of the 25 lesions had a transient tumour volume increase followed by tumour regression at 12 weeks. At 12 months 19 (37%) of lesions increased in volume in the extent of 41% in size. There was a significant higher tumour reduction in those carcinoma types that are considered as radiation sensitive. The best timing for follow-up imaging is at 6, 9 and 12 weeks to provide clinicians useful information. Conclusion: Stereotactic radiosurgery provide volume reduction in many brain metastases and it may be used alone or before whole brain radiation therapy to early tumour control. Follow-up MR imaging provide clinicians useful patient information aimed to make treatment decisions.