DOSIMETRIC CHARACTERISTICS OF PLANS RADIOSURGICAL TREATMENT OF MULTIPLE BRAIN METASTASES ON CYBERKNIFE AND GAMMA KNIFE
The aim of the study was to assess the quality of plans and comparison of the dosimetric parameters of dose distributions for the radiosurgery of multiple brain metastases on CyberKnife (CK) and Gamma- Knife (GK). 13 patients with multiple brain metastases (N≥4) treated with radiosurgery were selected for the investigation. Contours of targets and critical structures according to CT and MRI data were trans- ferred from MultiPlan to GammaPlan. The value of dose, covering 100 % of target volume, was equal for both devices. Following characteristics were calculated from dose-volume histogram (DVH): homogene- ity index (HI), coverage (CO), indexes of conformity (CIRTOG, nCI), gradient index (GI50, GI25) and doses in normal tissues (V10, V12, V10net, V12net). The original software was developed for the automate DVH pro- cessing. Following results we achieved while comparing indicators calculated for two devices. 1. De-pending on the targets volume: for volume [0.001;0.1) cm3 statistically reliable difference for CI, nCIRTOGwas no obtained; for volume [0.1;6] cm3 GK dose distribution is more conformal. For all target volumes CK gives more homogeneous dose distributions in target; the GK dose heterogeneity in target is accom- panied by high dose gradient out of the target and lower V10 and V10net values. 2. Independently on the to- tal number of lesions (N): nCI values are equal for CK and GK, however CIRTOG conformity is better on GK. For all N dose distribution in target is more homogeneous on CK, while dose gradients are higher on GK allowing more effective irradiation dose decreasing in brain.