Clinical and Volumetric Predictors of Local Control after Robotic Stereotactic Radiosurgery for Cerebral Metastases: Active Systemic Disease May Affect Local Control in the Brain
Aim. The aim of the study was to assess the association between physical and biological dose normalized to volume of the metastatic tumor as well as clinical factors with local control in patients with brain metastases who underwent robotic stereotactic radiosurgery.
Material and Methods. A cohort of 69 patients consecutively treated with robotic radiosurgery between 2011 and 2016 was analyzed. The patients were treated with either single fraction radiosurgery or hypofractionated regimens. Biologically effective dose (BED) was calculated assuming alpha/beta value = 10 and both physical dose and BED were normalized to the tumor volume to allow dose-volume effect evaluation. Moreover, clinical and treatment-related variables were evaluated to asses association with local control.
Results. A total of 133 tumors were irradiated and their volumes ranged between 0.001 and 46.99 cm3. Total dose, BED above 59 Gy, presence of a single metastasis, and extracranial progression were significantly associated with LC in univariate analysis. In multivariate analysis only presence of a single metastasis, BED10 > 59 Gy and extracranial progression as an adverse factor retained their significance. Excluding a priori the BED2/cm3 parameter which can be considered redundant in construction of the Cox model resulted with confirmation of significance of all of the remaining variables.
Conclusions. Hypofractionated treatment schemes have similar efficiency to single fraction treatment in terms of local control and the effect depends on BED irrespective of fractionation schedule. Effective control of extracranial sites of the disease is associated with probability of local control in the brain which is consistently lower in patients with multiple lesions.