ИСТИНА

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 ( N≥4) on CyberKnife (CK) and Gamma Knife (GK). Materials and methods. 13 patients with 68 brain metastases previously treated on the CK radiosurgery system were selected. Then contours of targets and critical structures according to CT and MRI data were transferred from MultiPlan to Leksell GammaPlan for reproducing treatment plan. The value of dose, covering 100% of target volume, was equal for both modality. Following characteristics were calculated from dose-volume histogram (DVH): homogeneity index (HI), coverage (CO), conformity indexes (CIRTOG, nCI), gradient indexes (GI50, GI25) and doses in normal tissues (V10, V12, V10net, V12net). The original software was developed for the automate DVH processing . Results. Following results we achieved while comparing indicators calculated for two SRS system. Depending on the targets volume: for volume [0,01;0,1) cm3 statistically reliable difference for CIRTOG, nCI was no obtained (CIRTOG: 1,523 ± 0,094 (GK) vs 1,623 ± 0,166 (CK), p=0,35; nCI: 1,535 ± 0,092 (GK) vs 1,623 ± 0,166 (CK) ,p=0,35); for volume [0,1;6] cm3 GK dose distribution is more conformal (nCI: 1,262 ± 0,075 (GK) vs 1,313 ± 0,079 (CK),p<0,05). For all volumes of target CK gives more homogeneous dose distributions in target (HI: 62,43 (35,18 – 81,48) % (GK) vs 18,25 (13,82 – 24, 30) % (CK), p <0,001); the GK dose heterogeneity in target is accompanied by high dose gradient out of the target and lower V10 and V10net values. Independently on the total number of lesions (N): nCI values are equal for CK and GK (1,211 ± 0,036 (GK) vs 1,332 ± 0,066 (CK) , p=0,25), however CIRTOG conformity is better on GK (1,151 ± 0,023 (GK) vs 1,332 ± 0,066 (CK), p<0,05). For all N dose distribution in target is more homogeneous on CK (62,22 (18,02 - 78,04) % (GK) vs 21,93 (20,16 - 23,75) % (CK),p< 0,001), while dose gradients are higher on GK allowing more effective irradiation dose decreasing in brain.