Page 35 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =treatment, were analyzed in order to determine the position accuracy and also to evaluate the intra- fraction motion. Finally, a MVCT post-treatment were also acquired in six patients underwent radiosurgery with HT.ResultsMean setup errors and standard deviations in phantom study were 0.0±0.1 mm, 0.1±0.3 mm, 0.1±0.3 mm, for the IEC-X, IEC-Y, IEC-Z directions and 0.3±0.3°, 0.2±0.2°, 0.2±0.2° rotational variations (pitch, roll, yaw), respectively. The mean vector displacement (v) was 0.4±0.2 mm. Moreover, the mean rotational variations could be considered negligible. The very low recorded values show that HT system is able to achieve treatment accuracy typical of SRS (v<1mm).The mean intra-fraction motions recorded in patients were 0.1±0.2 mm, -0.3±0.6 mm, 0.0±0.5 mm, 0.2±0.3°,0.2±0.4°, 0.0±0.3° for the IEC-X, IEC-Y, IEC-Z, pitch, roll and yaw, respectively. The mean vector displacement, in this case, was 0.8±0.3 mm, showing that the mask minimized the intra-fraction motion to a mean value < 1mm. No dependence on the treatment time was observed.ConclusionThe results of our study demonstrate that a mask-based fixation system have a high repositioning accuracy. Given the small setup error and intra-fraction movement, thermoplastic masks, combined with HT positioning system, may be used for high-precision treatments, like radiosurgery.26