Introduction: Contrast-enhanced MRI is the preeminent diagnostic exam for brain metastases (BM). Treatment of BM with stereotactic radiosurgery (SRS) requires accurate detection of lesion volume and size, which may improve with a time delay following administration of gadolinium-based contrast.
Methods: 53 volumetric MRIs from 38 patients were evaluated. All studies were performed on 1.5 and 3T magnets using Gadobenate dimeglumin contrast (MultiHance®). Three axial T1 post-contrast sequences were performed; one immediately after injection, and two at delays of 10 and 15 minutes. The studies were randomized and examined separately by 3 radiologists, who were blinded to their sequence. The number of tumors in each scan was compared with a Wilcoxon signed-rank test. Tumors >2 mm in diameter (n=234) were contoured using SRS planning software and a mixed model approach examined volume changes.
Results: The interclass correlations (<0.72) for all three sequences demonstrated high inter-rater reliability. At least one new lesion was detected in the 2nd scan as compared to the 1st in 35.3% of subjects, (range of new lesions detected 1-10). At least 1 new lesion was detected in the 3rd scan as compared to the 2nd in 21.6% of subjects (range 1-9). Between scans 1 and 3 additional tumors were seen on 41.2% of scans (range 1-14). There was a significant increase in number of BM detected from scans 1 to 2 (P < 0.0367), and scans 1 to 3 (P < 0.0264). We found an average 25.4% increase in BM volume between scan 1 and 2 (P<0.0001), and a 9% increase between scans 2 and 3 (P<0.0001).
Conclusions: In patients who undergo SRS of BM, delayed MRI after contrast injection increases number and volume of BM to be treated. To avoid missing or undertreating tumors, we recommend MRI be acquired between 10 and 15 minutes after contrast injection.
Patient Care: Imaging is critical to SRS treatment planning for brain metastases. Correctly identifying the number and volume of brain metastases improves patient management and prevents disease recurrence.
Learning Objectives: By the conclusion of this session, participants should be able to 1) describe the value of delayed MRI following administration of gadolinium-based contrast 2) consider implementing a delayed imaging protocol in clinical practice