Simultaneous integrated boost using stereotactic radiosurgery for resected brain metastases: rationale, dosimetric...

Radiosurgery has been shown to reduce the rates of local recurrence in the postoperative bed after the resection of brain metastases, but the ideal radiation dose has not been well defined.

To present dosimetric parameters and preliminary clinical outcomes for patients undergoing postoperative stereotactic radiosurgery (SRS) with simultaneous integrated boost (SIB) for brain metastases.

3 patients underwent surgery for a dominant metastatic focus and had residual or recurrent disease in the resection cavity. Our technique delivered a low dose to the resection cavity with an SIB dose to the gross tumor. Clinical target volume (CTV) was the magnetic resonance (MR)-defined resection cavity. Gross tumor volume (GTV) was the MR-defined residual disease. No additional margin was added to either the resection cavity or the residual disease area. Doses ranged from 14-15 Gy for CTV and 17-18 Gy for GTV prescribed to the 71%-78% isodose line. A traditional postoperative radiosurgery plan was constructed for each patient, and dosimetric values were compared using the paired t-test.

3 patients were treated at our institution using SRS with SIB. No patient experienced local recurrence. 2 patients developed distant brain failure (mean, 3.5 months). No grade 3 or greater toxicities were observed. The volume of brain receiving 12 Gy was significantly reduced using SIB compared with traditional postoperative SRS (𝑃 = .04). There were no differences in the maximum dose delivered to the tumor (𝑃 = .15) and cavity (𝑃 = .13). The average mean cavity dose was 16.20 Gy using the SIB plan, compared with 19.71 Gy using the traditional plan (𝑃 = .05).

In patients with either recurrent or residual disease following surgical resection, SRS using SIB is technically feasible and safe.