The impact of MRI steady-state sequences as an additional assessment modality in vestibular schwannoma patients after LINAC stereotactic radiotherapy or radiosurgery

Abstract

Purpose

Data concerning the clinical usefulness of steady-state sequences (SSS) for vestibular schwannomas (VS) after linear accelerator (LINAC) stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) are scarce. The aim of the study was to investigate whether SSS provide an additional useful follow-up (FU) tool to the established thin-layered T1 sequences with contrast enhancement.

Methods

Pre- and post-treatment SSS were identified in 45 consecutive VS patients (2012–2016) with a standardized FU protocol including SSS at 2–3 months and 6 months/yearly in our prospective database and were retrospectively re-evaluated. The SSS were used throughout for the segmentation of the cochlea and partly of the trigeminal nerve in the treatment planning. Data analysis included signal conversion in SSS and possible correlation with neuro-otological outcome and volumetric assessment after a certain time interval.

Results

The series included 42 SRS and 3 SRT patients (31 female/14 male; mean age 59.3 years, range: 25–81 years). An SSS signal conversion was observed in 20 tumors (44.4%) within a mean time of 11 months (range: 7–15 months). Mean FU time was 26 months (median of 4 FU visits) and demonstrated tumor volume shrinkage in 29 cases (64.4%) correlating with FU time (p = 0.07). The incidence rate of combined shrinkage and signal conversion (48.3%) compared to those without signal conversion (51.7%) did not differ significantly (p = 0.49). In case of an early signal conversion at the first FU, a weak statistical significance (p = 0.05) for a higher shrinkage rate of VS with signal conversion was found. Side effects in cases with signal conversion (9/20, 45%) were more frequently than without signal conversion (6/25, 24%) without reaching statistical significance (p = 0.13).

Conclusion

Our data confirmed the usefulness of SSS for anatomical segmentation of VS in LINAC-SRS/SRT treatment planning and add data supporting their potential as an adjunctive FU option in VS patients.

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