²³Na-MRI of recurrent glioblastoma multiforme after intraoperative radiotherapy: technical note.

Introduction: We report the first case of an intraoperative radiotherapy (IORT) in a patient with recurrent glioblastoma multiforme (GBM) who was followed up with a novel magnetic resonance imaging (MRI) method-(23)Na-MRI-in comparison to a standard contrast-enhanced (1)H-MRI and (18)F-FET-PET.

Methods: A 56-year-old female patient with diagnosed GBM in July 2012 underwent tumor resection, radiochemotherapy, and three cycles of chemotherapy. After a relapse, 6 months after the initial diagnosis, an IORT was recommended which was performed in March 2013 using the INTRABEAM system (Carl Zeiss Meditec AG, Germany) with a 3-cm applicator and a surface dose of 20 Gy. Early post-operative contrast-enhanced and 1-month follow-up (1)H-MRI and a (18)F-FET-PET were performed. In addition, an IRB-approved (23)Na-MRI was performed on a 3.0-T MR scanner (MAGNETOM TimTrio, Siemens Healthcare, Germany).

Results: After re-surgery and IORT in March 2013, only a faint contrast enhancement but considerable surrounding edema was visible at the medio-posterior resection margins. In April 2013, new and progressive contrast enhancement, edema, (23)Na content, and increased uptake in the (18)F-FET-PET were visible, indicating tumor recurrence. Increased sodium content within the area of contrast enhancement was found in the (23)Na-MRI, but also exceeding this area, very similar to the increased uptake depicted in the (18)F-FET-PET. The clearly delineable zone of edema in both examinations exhibits a lower (23)Na content compared to areas with suspected proliferating tumor tissue.

Conclusion: (23)Na-MRI provided similar information in the suspicious area compared to (18)F-FET-PET, exceeding conventional (1)H-MRI. Still, (23)Na-MRI remains an investigational technique, which is worth to be further evaluated.