ESTRO 37 Abstract book

ESTRO 37

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margin and all organs at risk (OARs) were delineated on the stable exhale phase. DWA is a system -specific arc technique (Vero SBRT system) that combines synchronized gantry-ring rotation with dynamic -MLC optimization. It was integrated in the RayStation TPS (RaySearch Laboratories, Sweden), which is using a collapsed cone dose calculation algorithm. Optimal plans were generated using multiple DWAs chosen from a set of template-based trajectories (Figure 1). All plans were evaluated using the RTOG high- and intermediate- dose spillage criteria: conformity index (CI), ratio of 50% isodose volume to the PTV (R50%), maximum dose 2 cm away from the PTV (D2cm), percent of normal lung receiving ≥ 20Gy (V20) and all other OAR constraints were evaluated. Dose delivery verification was performed with the Delta4 dosimeter. Results A total of 31 SBRT plans were analyzed. Coin lesions were planned with 51Gy/3fr (n=3). Subpleural or more centrally located lesions were treated with 48Gy/4fr (n=21) or 60Gy/8fr (n=7) depending on PTV volume and OAR constraints. Average PTV volume treated was 47.8cc (range, 7.9 - 130.3cc). Mean tumor diameter was 24mm (range, 8 - 39mm). Mostly 3 DWA were applied (range, 2 - 4) to allow intra-fraction cone-beam CT verification and to limit the amount of MUs per wave. Mean beam-on delivery time was 5.8 min (range, 2.9 - 10.1min). The template-based DWA solution could not be used in 2 cases, thus standard coplanar VMAT was used instead. The reason was collision detection during the dry-run test the first case, and insufficient planning CT scan length to allow non-coplanar dose calculation in the second case. The CI was >1.2 and < 1.5 for 7 plans, the R50% of 15 plans showed a minor violation. The cut-off volume that derived higher CIs and more low dose spillage was determined at 25cc. Except for peripheral tumors where a portion of the rib was included in the PTV, OAR constraints could be met. The average gamma (3%/3mm) passing rate for the DWA plans was 99.6% (range, 97.7- 100%). Conclusion DWA is a fast and smooth treatment approach that improves patient comfort and reduces the workload for RTTs. The current template-based solution presented some limitations, therefore the use of individualized DWA trajectories should be made available. The excellent QA results demonstrate a dosimetrically robust delivery. Better conformity and less violations on the R50% were observed for lesions larger than 25cc. PO-0997 Towards personalized dose-escalation in non- small cell lung cancer: Validation of published models M. Thor 1 , A. Jackson 1 , A. Iyer 1 , E. Bendau 1 , A. Fontanella 1 , A. Apte 1 , E. Yorke 1 , A. Rimner 2 , J. Deasy 1 1 Memorial Sloan Kettering Cancer Center, Medical Physics, New York- NY, USA 2 Memorial Sloan Kettering Cancer Center, Radiation Oncology, New York- NY, USA Purpose or Objective RTOG 0617 has demonstrated the need for patient- specific dose-escalation, derived from normal tissue complication probability (NTCP) models, of stage III non- small cell lung cancer (NSCLC) treatments. The goal of this work was to investigate the performance of eight previously published NTCP models for NSCLC in an

printing technology. Gafchromic EBT3 films were used for measurements of the dose distribution. They were cut as like shape of applicator and fixed around the applicator mounted to miniature brachytherapy source. EBT3 films were irradiated in the water for 5 minutes. Results Fabricated electronic brachytherapy source was stably operated at 50 kV, the current of brachytherapy source was 253 mA. The X-ray energy spectra was measured at 40kV and 50 kV. Both X-ray spectra have tungsten characteristics and broad bremsstrahlung X-rays with the energies up to 40keV and 50 keV respectively. The x-ray angular dose distribution was measured from +122.4° to - 122.4° at 1 cm in the air. The X-ray intensity difference in the range of 244.8° was about 20% with decrease 108.1 to 87.0±0.9 Gy/min. Percent depth doses(PDD) were measured without x-ray filter and with 1mm, 2mm x-ray filter. The PDD of without filter was more steeper dose gradient than PDDs of 1mm, 2 mm x-ray filter. The suitable treatment range can be controlled by changing of x-ray filter thickness and tube voltage. A dose of 9.8 Gy was delivered at 5 mm to hemisphere direction and average dose of 8.45±0.21 Gy was delivered to linear direction. The delivered dosage can be controlled by changing irradiation time, x-ray energy and dwell position of fabricated electronic brachytherapy source. Conclusion The study results show that the fabricated cylindrical applicator mounted miniature electronic brachytherapy source based on CNT field emission can potentially be applied for electronic intravaginal brachytherapy because of its low energy, steep dose gradient, dose distribution. Further work is needed to get homogeneous dose distribution around cylindrical applicator to verify optimization of dwell position and X-ray energy. PO-0996 Dynamic Wave Arc for lung SBRT: compliance with RTOG dosimetric criteria. C. Collen 1 , M. Burghelea 2 , R. Van den Begin 1 , G. Coussement 1 , B. Engels 1 , T. Gevaert 1 , M. De Ridder 1 1 Universitair Ziekenhuis Brussel, Radiotherapy, Brussels, Belgium 2 Universitair Ziekenhuis Brussel, Radiation Oncology, Brussels, Belgium Purpose or Objective Dynamic Wave Arc (DWA) is a novel non-coplanar VMAT solution clinically implemented in our department. We report on the compliance with RTOG 0813 and 0915 dosimetric criteria for lung SBRT using DWA. Material and Methods

This study evaluated the lung SBRT plans of patients enrolled in a prospective trial (NCT 02224547). Internal target volumes (ITVs) were generated combining gross tumor volumes of all 10 respiratory phases on a 4DCT. Planning target volumes (PTVs) consisting of ITV + 5 mm