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Background

Treatment of multiple brain metastases (BM) often involves surgical resection of one lesion combined with stereotactic radiotherapy (SRT) to the resection cavity and unresected BM. Intraoperative radiotherapy (IORT) is an emerging alternative for treating the resection cavity, potentially dosimetric benefits. This study aimed to compare the dosimetry of treating the resection cavity with IORT versus adjuvant SRT when combined with SRT for additional unresected BM.

Methods

Ten patients with BM who received adjuvant SRT to the resection cavity plus concurrent SRT to additional BM (adjuvant SRT + SRT to BM group) and 4 patients with IORT and SRT to BM were identified. Post-hoc IORT plans were calculated for IORT patients and summed with corresponding SRT plans. Additionally, patients from the adjuvant SRT + SRT to BM group served as templates for IORT simulation and the simulated IORT plans were also summed with the corresponding plans for SRT to residual BM. The simulated IORT cases were then pooled with the actual IORT cases, forming the IORT + SRT to BM group. Brain dose exposure (V12Gy, V18Gy, V20Gy, V24Gy, V25Gy, and V30Gy) and maximum doses (D0.035 cm³) to the brainstem and optic tract were evaluated.

Results

The IORT + SRT to BM group showed significantly lower brain dose exposure across all metrics (V12Gy-V30Gy) compared to the adjuvant SRT + SRT to BM group (p < 0.05 for all). Maximum doses to organs at risk were lower in the IORT + SRT to BM group, with mean D0.035 cm³ reduced by 37.7% for the brainstem (3.51 Gy vs. 5.65 Gy, p = 0.292) and significantly reduced by 57.5% for the optic tract (0.89 Gy vs. 2.10 Gy, p = 0.040).

Conclusions

IORT in combination with SRT for additional BM demonstrated superior dosimetric properties compared to adjuvant cavity SRT plus concurrent SRT to BM.

AbstractSection Trial registration

Not applicable (Retrospective dosimetric study).