Page 60 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =Use of a 3D dosimeter to assess dosimetric leaf separation constancy over timePreliminary resultsM. BOCCIA1, C. OLIVIERO2, S. CLEMENTE2, S. RICCARDI3, N. FRANZA4, R. NIGRO31 Università degli Sudi di Napoli "Federico II",2 Azienda Ospedaliera Universitaria Federico II, Napoli 3 Ospedale San Camillo De Lellis, Rieti4 Dosimetrica noc.inf (SA)IntroductionDynamic multi leaf collimator (DMLC) mounted on modern accelerators requires a fine modeling to ensure the best performace. Among these, DLS (dosimetric leaf separation) is one of the most sensitive parameter that could affect the accuracy of delivery. An error in the measure of the DLS during commissioning or a mechanical variation of leaves gap due to wear motor and mechanical backlash of the MLC may lead to a significant difference between the delivered and planned dose on TPS. The aim of this work is to measure and monitor over time the DLS parameter, using two version (as bi-centric study) of a bi-planar diode array phantom: Delta4 and Delta4 Plus (Scandidos, Uppsala, Sweden). The dosimetric impact of a DLS error on SBRT plans for multiple treatment sites were also evaluated.Materials & MethodsTHE DLS PARAMETERS OF THE HIGH DEFINITION 120 LEAF MLC (HD MLC) AND THE 120 LEAF MLC (MILLENNIUM) MOUNTED ON A VARIAN TRUEBEAM STX (TB) AND A VARIAN CLINAC 2100 C/D RESPECTIVELY WERE INVESTIGATED WITH A DEDICATED DELTA4 ANALYSIS TOOL NAMED MACHINE QA (QUALITY ASSURANCE). THEN, 30 SBRT PLANS, WERE CALCULATED WITH PINNACLE 9.10 (PHILIPS) AND ECLIPSE 13.5 (VARIAN MEDICAL SYSTEMS) USING BOTH THE MEASURED DLS VALUE AND AN51