Page 41 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =Validation of a delivery quality assurance method for CyberKnife tumor-tracking stereotactic treatmentsE. MASTELLA1,2, S. VIGORITO2, E. RONDI2, G. PIPERNO3, A. FERRARI3, E. STRATA3, D. ROZZA3, B.A. JERECZEK-FOSSA3,4, F. CATTANI 21Fondazione CNAO – Centro Nazionale di Adroterapia Oncologica, Unità di Fisica Medica, I-27100 Pavia, Italia.2IEO – Istituto Europeo di Oncologia, Unità di Fisica Medica, I-20141 Milano, Italia3IEO – Istituto Europeo di Oncologia, Divisione di Radioterapia, I-20141 Milano, Italia.4Università degli Studi di Milano, I-20122 Milano, Italia.IntroductionThe aim of this work was to evaluate the geometric and dosimetric accuracy of the CyberKnife Synchrony Respiratory Tracking System (RTS) and to validate a method for pretreatment patient- specific delivery quality assurance (DQA).Materials and MethodsAn EasyCube phantom was mounted on the ExacTrac gating phantom, which can move along the superior–inferior (SI) axis of a patient to simulate a moving target. We compared dynamic and static measurements. For each case, a Gafchromic EBT3 film was positioned between 2 slabs of the EasyCube, while a PinPoint ionization chamber was placed in the appropriate space. There were 3 steps to our evaluation: 1) the field size, the penumbra, and the symmetry of 6 secondary collimators were measured along the 2 main orthogonal axes. Dynamic measurements with deliberately simulated errors were also taken. 2) The delivered dose distributions (from step 1) were compared with the planned ones, using the γ analysis method. The γ passing rates were evaluated using 3 acceptance criteria: 3%local dose difference (LDD)/3mm, 2%LDD/2mm, 3%LDD/1mm).32