ESTRO 36 Abstract Book

S282 ESTRO 36 _______________________________________________________________________________________________

treatments. Measurements performed by DUO are compared to EBT3 film for cases with and without motion, as well as motion with the MLC tracking algorithms enabled. Results Fig.1 shows the comparison of the SUP-INF 3DCRT static beam profile measured by DUO in the solid water phantom and the same beam delivered using a patient specific breathing motion pattern with and without MLC tracking. The predictive tracking has a lower discrepancy with respect to the static beam showing a reduction of the beam misplacement from ±70% to ±12% and ±58% to 20% in the solid water and timber phantom respectively. Discrepancies between DUO and EBT3 are within 2.4% overall. Temporal analysis shows the interplay effects between beam position and target motion with clear difference between predictive and non–predictive algorithms.

Figure 2: Gamma passing rate for the plans (6 MV) with errors, normalized to the detectability threshold, measured by SRS, 729 (merged) and 1500 (merged) dosimeters. Conclusion Improving the resolution of the planar detector used for QA increases the points with gamma<1. The SRS matrix can detect delivery errors in almost all cases at 2%L/1mm. Reference [1] G. A. Ezzell et al., 'IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119,” Med. Phys 36 , 5359 (2009) . OC-0532 QA of stereotactic radiotherapy combined with electromagnetic MLC tracking by a silicon detector M. Petasecca 1 , M.K. Newall 1 , M. Duncan 1 , V. Caillet 2 , B. James 1 , J.T. Booth 2 , M.L.F. Lerch 1 , V. Perevertaylo 3 , P. Keall 4 , A.B. Rosenfeld 1 1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong NSW, Australia 2 Royal North Shore Hospital, Northern Sydney Cancer Centre, Sydney - NSW, Australia 3 SPA-BIT, Microelectronics, Kiev, Ukraine 4 University of Sydney, Radiation Physics Laboratory- School of Medicine, Sydney - NSW, Australia Purpose or Objective Optimisation of treatment delivery based on patient- specific intra-fractional changes in anatomy is compulsory in organs affected by breathing or cardiac cycle. MLC tracking by using electromagnetic transponders implanted in the tumor is one strategy to adapt the beam shape and position in real-time. MLC tracking combined with highly conformal delivery modalities such as SRT has been shown to be feasible for lung and liver cancer treatment on a standard linac. QA for such treatments requires specialised tools with high spatial resolution for accurate measurement of sharp dose fall-off and high timing resolution for verification of the interplay of effects between organ motion and modulation of the irradiation fields. A dosimetry system for fast verification of the performance of MLC tracking in SRT is proposed. Material and Methods A monolithic 2D silicon detector, known as DUO, has been developed and comprises 512 pixels each with size 40x800mm 2 and pitch 0.2mm arranged in two linear orthogonal arrays. The DUO is read out by a multichannel electrometer synchronised with the linac. For evaluation of the accuracy and effectiveness of MLC tracking in both soft tissue and lung, we placed DUO in a solid water phantom, homogeneous timber phantom and timber phantom with a solid water spherical hidden target of 1 cm diameter. We installed the phantoms on a moving platform supplied with a set of patient-specific motion patterns. The commercial Calypso system provides real- time position of the target to the MLC software which has been tested using a predictive and non-predictive tracking algorithm. We planned the target dose using 3DCRT (a 2 cm diameter field) and IMRT (with 5mm margins)

Conclusion It is observed that motion distorts the planned dose profile in both solid water and lung phantom. MLC tracking reduces dose smearing significantly as demonstrated by the no-motion and motion-tracking results. The DUO detector has proven to be an effective tool for pre- treatment verification of real-time adaptive stereotactic deliveries with both high spatial resolution for dose profiling and high temporal resolution for pulse by pulse dose reconstruction. S. Pallotta 1 , L. Foggi 1 , S. Calusi 1 , L. Marrazzo 1 , C. Talamonti 1 , L. Livi 2 , G. Simontacchi 2 , R. Lisci 3 1 University of Florence, Department of Medical Physics, Firenze, Italy 2 University of Florence, Department of Radiotherapy, Firenze, Italy 3 University of Florence, Department of Agricultural- Food and Forestry System, Firenze, Italy Purpose or Objective Dose delivery to moving targets can be approached following different strategies. For stereotactic radiotherapy treatments motion-encompassing methods, respiratory-gating techniques and respiration- synchronized techniques permit the treatment during lesions motion using different dose planning/delivering solutions. In all cases the complexity of the proposed methods needs the development of solutions for accurate Quality Assurance tests as stated also by AAPM TG76. For this purpose we developed a new phantom: ADAM (Anthropomorphic Dynamic breAthing Model), capable of simulating realistic patient movements. The phantom and some preliminary tests showing ADAM performances are here presented. Material and Methods ADAM is a 3D printed anthropomorphic phantom created using a real patient CT data. The central portion of the OC-0533 ADAM: a breathing phantom for testing radiotherapy treatment on moving lesions