Abstract
Stereotactic radiosurgery (SRS) to a surgical cavity after brain metastasis resection is a promising treatment for improving local control. The optimal timing of adjuvant SRS, however, has yet to be determined. Changes in resection cavity volume and local progression in the interval between surgery and SRS are likely important factors in deciding when to proceed with adjuvant SRS.We conducted a retrospective review of patients with a brain metastasis treated with surgical resection followed by SRS to the resection cavity. Post-operative and pre-radiosurgery magnetic resonance imaging (MRI) was reviewed for evidence of cavity volume changes, amount of edema, and local tumor progression. Resection cavity volume and edema volume were measured using volumetric analysis.We identified 21 consecutive patients with a brain metastasis treated with surgical resection and radiosurgery to the resection cavity. Mean age was 57 yrs. The most common site of metastasis was the frontal lobe (38%), and the most common primary neoplasms were lung adenocarcinoma and melanoma (24% each). The mean postoperative resection cavity volume was 7.8 cm3 and shrank to a mean of 4.5 cm3 at the time of repeat imaging for radiosurgical planning (median 41 days after initial post-operative MRI), resulting in a mean reduction in cavity volume of 43%. Patients who underwent pre-SRS imaging within 1 month of their initial post-operative MRI had a mean volume reduction of 13% compared to 61% in those whose pre-SRS imaging was ≥1 month (p=0.0003). Post-resection edema volume was not related to volume reduction (p=0.59). During the interval between MRIs, 52% of patients showed evidence of tumor progression within the resection cavity wall. There was no significant difference in local recurrence if the interval between resection and radiosurgery was <1 month (n=8) versus ≥1 month (n=13, p=0.46).These data suggest that the surgical cavity after brain metastasis resection constricts over time with greater constriction seen in patients whose pre-SRS imaging is ≥1 month after initial post-operative imaging. Given that there was no difference in local recurrence rate, the data suggest there is benefit in waiting in order to treat a smaller resection cavity.
Highlights
Metastases are the most common intracranial tumors in adults, affecting 10-40% of cancer patients and resulting in approximately 170,000 new cases per year [1,2]
Replacement of WBRT with adjuvant stereotactic radiosurgery (SRS) to the surgical resection cavity has been advocated as a means of providing local control while minimizing the adverse effects associated with WBRT, and several studies have demonstrated comparable control rates between SRS and WBRT [6]
Jarvis et al, have reported dynamic changes in brain metastasis resection cavity volume and showed that cavities may be just as likely to expand in the interval between surgery and SRS as they are to constrict [10]
Summary
Metastases are the most common intracranial tumors in adults, affecting 10-40% of cancer patients and resulting in approximately 170,000 new cases per year [1,2]. Recently reported that the greatest amount of resection cavity constriction occurs in the immediate postoperative period This group performed adjuvant SRS relatively soon after surgical resection (median time from surgery to SRS 20 days) with no patients undergoing a pre-SRS MRI scan more than 33 days after surgery. We sought to determine if there were more long-term dynamic volume changes in the surgical resection cavity that would affect optimal timing of adjuvant SRS and whether there was any relationship to the amount of surrounding edema or the pathologic tumor type
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