Predictors of outcome following Gamma Knife surgery for acromegaly

Abstract

Object Gamma Knife surgery (GKS) is gaining popularity in the treatment of patients with acromegaly after transsphenoidal tumor excision. In this paper, the authors examine the efficacy of GKS and predictors for biochemical remission. Methods The authors retrospectively reviewed data spanning the period 1997–2008 in their hospital Gamma Knife statistics database. Forty patients with a mean age of 64 years (range 19–73 years) underwent GKS for acromegaly during that period. Transsphenoidal subtotal tumor excision had been performed prior to GKS in all these patients, except for 3 deemed to be at high surgical risk. All GKS treatment plans were formulated by the same team that performed the microsurgical procedures. Biochemical remission was defined as a growth hormone (GH) level < 2 ng/ml and an insulin-like growth factor–I level that was considered normal with reference to the patient's age and sex. The mean follow-up period after radiosurgery was 73.8 months (range 12–132 months). Results Three patients died during the study period of causes unrelated to surgery or GKS. Twenty-nine patients (72.5%) underwent 1 radiosurgery session, and 11 patients (27.5%) required 2 radiosurgery sessions. Among the patients who underwent 1 radiosurgery session, excellent responses (76%–100% reductions in tumor size, GH level, and insulin-like growth factor–I level) were observed in 18 (62%; p < 0.0001), 20 (69%; p < 0.0001), and 5 patients (17%; p = 0.21), respectively. Tumors < 1 cm3 and those with no evidence of cavernous sinus extension were statistically significantly related to a good response in tumor size reduction (p = 0.029 and p = 0.0016, respectively). Subgroup analyses were performed in patients who attained biochemical remission in GH levels; the subgroups included patient sex, patient age, target volume, isodose volume, prescribed dose and isodose, pre-GKS GH level, and evidence of cavernous sinus extension. Only male sex was found to be a statistically significant predictor of good hormone regulation (p = 0.0124). The presence of a cavernous sinus extension was the statistically significant predictor of poor hormone control (p = 0.0011) in our study. Conclusions Subtotal tumor excision followed by GKS was an effective treatment for acromegaly. Tumors < 1 cm3 and those with no evidence of cavernous sinus extension responded well to treatment. Male sex and absence of cavernous sinus involvement can be regarded as predictors of biochemical remission.