Conclusions. The IVD procedure with SOFTDISO resulted easily implementable and able to individuate errors with a limited workload. https://doi.org/10.1016/j.ejmp.2018.04.126 116. Characterization of a commercial Optically Stimulated Luminescence (OSL) dosimetry system for VMAT treatments verifications E. Bonanno a , A.G. Amico b , N. Cavalli a , A. D’Agostino a , A. Girlando a , G. Pisasale a , N. Ricottone a , C. Marino a,b a HUMANITAS-Centro Catanese di Oncologia, Medical Physics Depart- ment, Catania, Italy b Medical Physics School, University of Catania, Catania, Italy Purpose. A new commercial OSL dosimetry system was studied to analyze the possibility of its using for VMAT planning checks. The system was characterized and tested in conventional dose range (0,25–3 Gy). Methods. NanoDots (Landauer Ò ), matched with readout system MicroSTARii TM , are made of Al 2 O 3 :C, which show sensitivity 40–60 times the TL one. The characterization included: signal decrease for repeated readings; angular, energy and dose-rate dependence. A calibration curve was obtained in range 0,25–3 Gy, using RW3 slab phantom and 6 MV photon beam. A VMAT plan, regarding lung lesion, was designed and optimized with: 6 MV, 600 MU/min, Eclipse TPS and Acuros XB algorithm (13.6.23) for TrueBeam 2.5. Verification plans were created starting from the first one, both in RW3 and in anthropomorphic phantom. The measurement in RW3 was compared with the pin point measurement value. In anthropo- morphic phantom, got in position using CBCT, the OSLDs were allo- cated in four apposite inserts, with different densities, both inside and outside the PTV. Results. The OSLDs, exposed to 1 Gy and read for 5 times, showed a maximum deviation from the 1nd reading of 2% with a variation coefficient of 0,8%. In the range 0.25–3 Gy, the OSLDs exhibited a 2nd order polynomial fit with dose related to 6 MV energy. The 10 MV polynomial fit moved away from 6 MV one with increase of dose, but into error bars (Fig.). Angular dependence response presented a maximum deviation from the 0° angle reading of 2,7%, correspond- ing at 270° angle. A dose-rate dependence was not found in the range 200–600 MU/min. The results of the comparison Pin Point VS OSLD VS TPS in RW3 and in anthropomorphic phantom are showed in the Table. Conclusions. The OSLD exhibited to be feasible for VMAT verifica- tions in conventional fractionated treatments using 6 MV photon beams. https://doi.org/10.1016/j.ejmp.2018.04.127 117. Synergistic use in external beams breast irradiation of two in vivo monitoring devices: A study in anthropomorphic female phantom C. Arilli a , Y. Wandael b , M. Casati a , L. Marrazzo a , G. Galeotti b , S. Calus c , M. Grusio d , S. Pallotta a,c , C. Talamonti c,a a AOU Careggi, Medical Physics Unit, Florence, Italy b AOU Careggi, Radiotherapy Unit, Florence, Italy c University of Florence, Department of Experimental and Clinical Biomedical Sciences ‘‘Mario Serio”, Florence, Italy d Best Medical SRL, Italy Purpose. To evaluate the sensitivity of two systems for in vivo dosimetry, the IQM detector (iRT Systems GmbH, Koblenz, Germany) and the SoftDiso software (Best Medical Srl, Italy), in detecting deliv- ery and set-up errors which can occur in 3DCRT external breast irradiation. Methods. IQM is a transmission chamber mounted below the MLC, whose signal is dependent on radiation fluence [1]. SoftDiso recon- structs the dose distribution at the isocenter plan using the informa- tion derived from treatment EPID images and calculates the R-value, defined as the ratio between measured and planned dose at the isocenter [2]. To simulate the female anatomy, the ALDERSON- RANDO phantom was modified with two silicon breast prosthesis. A 3DCRT plan of left breast was created and modified to mimic out- put errors (adding 2–3-5–10 MU) and a jaw position error (opening and closing one jaw 2–3-5–7 mm). Additionally set-up errors were simulated by moving the phantom in anterior-posterior direction (2–3-5–10 mm) and by rotating it (1°–2.8°). The deviations of IQM signal and R-value from the original values were evaluated for all plans and phantom positions. Results. The IQM signal and R-value linearly increase with the MU increment (R 2 = 1 and 0.97 respectively) (Fig. 1a). The IQM signal is linearly correlated with the jaws position (R 2 = 0.93 and 0.97 for close and open jaw), while R-value is less sensitive to jaws position- y = -2E-09x 2 + 0,0025x - 0,7769 y = -2E-09x 2 + 0,0025x - 1,2196 0 50 100 150 200 250 300 350 0 50000 100000 150000 200000 Dose (cGy) Counts 6X 10X RW3 Phantom Dose Pinpoint (cGy) Dose OSLD (cGy) Dose TPS (cGy) Dose difference OSLD- PinPoint (%) 222,90 223,41 224,8 0,23 Anthropomorphic Phantom OSLD Dose OSLD (cGy) Dose TPS (cGy) Dose difference OSLD- TPS (%) Position 1 205,97 200 2,99 Position 2 98,53 101,65 -3,07 Position 3 126,22 131,90 -4,30 Position 4 149,88 147,62 1,53 Abstracts / Physica Medica 56 (2018) 133–278 135