ESTRO 37 Abstract book

S1199

ESTRO 37

These results are collected in Fig.2. This figure shows the behaviour of the voltage (mV), the current (mA) and the frequencies (Hz) in S1 and S2 operating states during BaseLine session (a). The same figure displays the behaviour of the voltage (b), the current (c) and the frequency (d) measured in the five sessions during S1 state, respectively.

differences for various OARs range from ~1 to ~5 Gy with 95% CI for the mean. The H plan QA results gave passing rates of 90% or higher for γ: 3%, 3mm (global) with the H IMRT delivery time being comparable to the RA TB delivery time.

Fig. 1: DVH for OARs, with H lower mean doses compared to the TB

Conclusion In patients with heart failure, guarantee VAD functionality for any type of dose is crucial. In this work, we showed that the pump continued its proper work after irradiation under high-energy photon beams. Future measurements will involve in vitro investigation of the system by simulating some typical radiotherapy treatments using 18MV energy photon beams where the influence of the neutron activation on the components can become important. EP-2166 Halcyon clinical performance evaluation for Head and Neck treatments compared to Truebeam D. Mihailidis 1 , R. Scheuermann 1 , C. Kennedy 1 , L. Brady 1 , L. Dong 1 , J. Metz 1 1 PENN-Perelman Center for Advanced Med, Radiation Oncology, Philadelphia, USA Purpose or Objective Evaluate the dosimetric performance and delivery of the Varian Halcyon TM (H) system and compare it with that of the Varian Truebeam TM (TB). Halcyon is the new radiotherapy platform that offers a single 6X-FFF straight-through linac with a new jawless fast dual level stacked MLC system, all optimized for rapid intensity modulated deliveries. This is our initial clinical experience for Head and Neck (H&N) treatments compared to the Truebeam platform. Material and Methods The dosimetric and delivery performance of the first clinical H system was studied at UPenn for a number of H&N patients. Based on our experience with the prototype system, fast IMRT delivery resulted in superior dosimetric results than VMAT (RapidArc) delivery for the H 1 . For our clinical implementation, H&N cases were planned for IMRT on the H and were compared with the TB VMAT plans and delivery times. For our first seven H&N patients, the comparison was based on dose distributions, plan verification and quality assurance accuracy, and the overall delivery times of the two systems. Our institutional prescriptions and optimization objectives were used for the plan optimization and the plans were reviewed and evaluated by the same clinician. The MVCBCT image dose is part of the H workflow and is included in the plan optimization for the H. Results In six cases, IMRT plans on the H were dosimetrically superior to the VMAT plans on the TB in that the OARs received lower mean doses. In 1 case, the TB VMAT plan was superior. DVHs between H and TB plans for OARs, with most OARs for the H plan receiving lower doses for the complex H&N cases, are shown in Fig. 1. The dose

Fig. 2: OAR dose differences TB minus H.

Conclusion The first clinical Halcyon system was implemented for H&N patients with overall comparable or superior performance for fast IMRT delivery compared to the Truebeam system. We are currently accruing more H&N patients and the additional data will also be presented. In addition, we are also performing studies for other treatment sites. 1 D. Mihailidis et al., Dosimetric advantage of IMRT compared to VMAT for H&N plans using a prototype jawless and fast MLC system. Med. Phys. 44 , (2017) 2945 EP-2167 Commissioning of the Elekta APEX dynamic micro multi-leaf collimator C. Ferrer 1 , R. Plaza 1 , C. Huertas 1 , Z. Aza 1 , R. Morera 2 , A. Serrada 1 1 Hospital universitaria La Paz, Radiofísica y Radioprotección, Madrid, Spain 2 Hospital universitaria La Paz, Oncología Radioterápica, Madrid, Spain Purpose or Objective APEX is the last model of micro multi-leaf collimator (mMLC) produced by Elekta, which attaches to the Linac head, for its use in Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT). This work studies its dosimetric and geometric characteristics, including mechanical stability, to achieve the state of reference of this add-on mMLC. Material and Methods All measurements have been realized on an 6MV Elekta Synergy linear accelerator equipped with a 160-leaf Agility MLC, with APEX attached to it. APEX weights 50 kg and consists of 56 pairs of tungsten alloy leaves with nominal width of 2.45 mm at the isocenter, which permits a maximum field of 12cm x 14 cm. The leaf design is double focused, with no tongue and groove design. Measurements of dose distribution, radiation penumbra and field factors were carried out using an IBA CC13 and