Page 42 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =3) The DQA plans for 6 clinical patients were irradiated in different dynamic conditions, to give a total of 19 cases. The measured and planned dose distributions were evaluated with the same γ- index criteria used in step 2 and the measured chamber doses were compared with the planned mean doses in the sensitive volume of the chamber.Results1) A very slight enlargement of the field size and of the penumbra was observed in the SI direction (on average<1mm), in line with the overall average CyberKnife System error for tracking treatments. 2) Comparison between the planned and the correctly delivered dose distributions confirmed the dosimetric accuracy of the RTS for simple plans. The multicriteria ã analysis was able to detect the simulated errors, proving the robustness of our method of analysis. 3) All of the DQA clinical plans passed the tests, both in static and dynamic conditions. No statistically significant differences were found between static and dynamic cases, confirming the high degree of accuracy of the RTS (see Table 1).ConclusionsThe presented methods verified the mechanical and dosimetric accuracy of the Synchrony RTS. Our measurements confirmed the fact that the RTS, if used properly, is able to treat a moving target with great precision. By combining PinPoint ion chamber, EBT3 films, and gamma evaluation of dose distributions, our DQA method robustly validated the effectiveness of CyberKnife and Synchrony System.Static cases Dynamic cases p-values3%LDD/3mm96.1 ± 4.5 95.1 ± 6.1 0.69 (%)2%LDD/2mm98.8 ± 1.3 98.4 ± 1.7 0.493%LDD/1mm98.1 ± 2.2 97.6 ± 2.4 0.63<ΔD>(%)2.7 ± 2.0 3.1 ± 1.8 0.64Table 1. Comparison between the mean gamma passing rates and the mean PinPoint dose differences for static and dynamic cases created for delivery quality assurance on patient plans. p-values were calculated with Student’s paired t-tests.Note: = mean gamma passing rates; LDD = local dose difference. <ΔD> = mean PinPoint dose differences.33