What is your technique for MRI to CT fusion for intracranial SRS planning?

Acurrate fusion has become a real concern with single isocenter VMAT and mulitple small peripheral mets, as there are many ROIs. Todd, the abstract you cited for fusion on the pediatric protocol: 1.8 mm average error with 2 mm standard deviation (https://www.ncbi.nlm.nih.gov/pubmed/20381270)

Present...

Rigid based registration is performed for cranial lesions while deformable registration may be required for extra-cranial sites. Among other factors the agreement accuracy will be affected by the imaging site and technique, magnitude of rotational discrepancies between the studies, patient motion ...

I'm reminded of that old Groucho Marx line: "Who are you going to believe, me or your lying eyes?" CT is, relatively speaking, more spatially fidelitous whereas, relatively, MRI is less so. This fact is why, even after an "auto-match," one can sometimes see obvious niggling anatomic and/or target mi...

Agree with all the above. Contrasted CT radiosurgery sim is imperative, esp. in metastatic cases (and of course CTA will be mandatory in an AVM case e.g.). I feel very confident when I can spot the target well on CT, as at the end of the day this is the dataset upon which we 1) ultimately contour us...

If you have a siemens scanner, here are mri protocols that minimize distortion/optimized for radiation planning and fusion

https://usa.healthcare.siemens.com/magnetic-resonance-imaging/magnetom-world/hot-topics/mri-in-radiation-therapy/protocols