Pre-operative stereotactic radiosurgery treatment is preferred to post-operative treatment for smaller solitary brain metastases

Abstract Background While the optimal combination of whole-brain radiotherapy (WBRT), stereotactic radiosurgery (SRS) and surgical resection in the treatment of brain metastases, is controversial, the addition of SRS to surgical resction of solitary metastasis may enhance local control while potentially minimizing toxicity associated with adjuvant WBRT. This study seeks to determine whether pre-operative SRS to the lesion versus post-operative SRS to the resection bed may reduce irradiation of adjacent normal brain tissue. Methods A retrospective study of 12 patients with 13 surgically resected cerebral metastases was performed. The pre-operative contrast-enhancing tumors and post-operative resection cavities plus any enhancing residual disease were contoured to yield the gross target volume (GTV). In turn these GTV’s were uniformly expanded by 3-mm to generate the pre-operative, as well as post-operative planning target volume (PTV.) For each lesion, a 7-static-conformal-beam, non-coplanar plan utilizing 6 MV photons was generated to encompass the PTV within the 85% isodose line. Excess normal brain volume irradiated was defined as the volume outside the GTV receiving the prescribed dose. Results When lesions were divided into two groups - Group A (pre-operative GTV’s 15 cc, n = 4) - the average volume of normal brain irradiated was significantly smaller if pre-operative SRS was used for treatment of lesions in Group A (9.5 vs. 16.8 cc, paired t-test, p = 0.0045). In contrast, this volume was smaller for Group B lesions if post-operative SRS was used for treatment of these lesions (27.6 vs. 51.2 cc, p = 0.252). A comparison of groups with respect to mean volume differences between pre- and post-operative SRS was significantly different (two-sample t-test p = 0.016). GTV and the difference between pre- and post-operative volume were highly correlated (Pearson correlation = −0.875, p