Radiosurgery-induced early changes in peritumoral tissue sodium concentration of brain metastases

by Arne Mathias Ruder, Sherif A. Mohamed, Michaela A. U. Hoesl, Eva Neumaier-Probst, Frank A. Giordano, Lothar Schad, Anne Adlung

Background

Stereotactic radiosurgery (SRS) is an effective therapy for brain metastases. Response is assessed with serial ¹H magnetic resonance imaging (MRI). Early markers for response are desirable to allow for individualized treatment adaption. Previous studies indicated that radiotherapy might have impact on tissue sodium concentration. Thus, ²³Na MRI could provide early quantification of response to SRS.

Purpose

We investigated whether longitudinal detection of tissue sodium concentration alteration within brain metastases and their peritumoral tissue after SRS with ²³Na MRI was feasible.

Study type

Prospective.

Population

Twelve patients with a total of 14 brain metastases from various primary tumors.

Assessment

²³Na MRI scans were acquired from patients 2 days before, 5 days after, and 40 days after SRS. Gross tumor volume (GTV) and healthy-appearing regions were manually segmented on the MPRAGE obtained 2 days before SRS, onto which all ²³Na MR images were coregistered. Radiation isodose areas within the peritumoral tissue were calculated with the radiation planning system. Tissue sodium concentration before and after SRS within GTV, peritumoral tissue, and healthy-appearing regions as well as the routine follow-up with serial MRI were evaluated.

Statistical tests

Results were compared using Student’s t-test and correlation was evaluated with Pearson’s correlation coefficient.

Results

We found a positive correlation between the tissue sodium concentration within the peritumoral tissue and radiation dosage. Two patients showed local progression and a differing tissue sodium concentration evolution within GTV and the peritumoral tissue compared to mean tissue sodium concentration of the other patients. No significant tissue sodium concentration changes were observed within healthy-appearing regions.

Conclusion

Tissue sodium concentration assessment within brain metastases and peritumoral tissue after SRS with ²³Na MRI is feasible and might be able to quantify tissue response to radiation.