Dosimetric comparison of between multileaf and fixed cone collimator plans with cyberknife-M6 in the benign skull base tumors

Abstract

CyberKnife (CK) is a SRS technique that ensures highly conformal dose distrubutions using a linac based robotic arm and image guidance with real-time tumor tracking. We aimed to retrospectively evaluate the clinical benefit and dosimetric outcomes of MLC and fixed cone-plans. Eleven acoustic schwannoma and 20 glomus jugulare patients' plans were retrospectively re-planned and analyzed. Treatment time, homogenity index (HI), conformity index (CI) and gradient index (GI) for PTV, volumetric doses of brain and brainstem, cochlea, beams and monitor units (MUs) were compared between MLC and fixed collimator planning system. The cochlea dose was observed significantly decrease in MLC plans (p= 0.023). Brainstem maximum point dose and also V10 Gy and V15 Gy of brain were significantly lower in MLC plans (p= 0.021, p= 0.014, p= 0.000, retrospectively). MLC plans consist less nodes and segments in comparison to fixed plans, also has less MU and shorter deliver treatment time (p= 0.00). The average delivered MUs in MLC plans are lower by 45% (p= 0.000). We confirmed the feasibility of time delivery effiency and reduced delivered MU in MLC planning techniques. Our analysis revealed that MLC plans have almost equivalant treatment plans with the fixed ones. The most precious finding is the MLC plans obtained higher protection on critical structures and consistently showed better dose gradient fall which is important for toxicity and second malignancies.