ESTRO 38 Abstract book

S52 ESTRO 38

Hospital, Department of Oncology, Aarhus, Denmark ; 3 Leiden University Medical Centre, Department of Clinical Oncology, Leiden, The Netherlands; 4 Cambridge University Addenbrooke’s Hospital, Department of Radiotherapy, Cambridge, United Kingdom; 5 University Medical Center Utrecht, 6 Department of Radiotherapy, Utrecht, The Netherlands Purpose or Objective The international, multicentre EMBRACE II study combines Image‐Guided Adaptive Brachytherapy for cervix cancer with an advanced protocol for external beam radiotherapy (EBRT) with specific target volume selection, contouring and treatment planning procedures. Well‐defined EBRT is an integral part of the overall treatment strategy with the primary aim of improving nodal control and reducing morbidity. Before entering EMBRACE II, institutes had to go through accreditation regarding EBRT and brachytherapy. This study describes the development of EBRT plan quality through the accreditation dummy‐run. Material and Methods The EMBRACE II EBRT planning concept is based on improved conformality[1] through eased coverage criteria for planning target volumes (PTV45Gy: V95%≥95% and Nodal PTV D90%≥98%) with the aim to reduce overall irradiated volume and spare OARs. Lymph nodes are irradiated by a simultaneous integrated boost and by coverage probability planning it is ensured that 98% of each nodal CTV is covered by 100% of the prescribed dose. As part of accreditation, a treatment planning dummy‐run in combination with educational blocks and submission of an examination case was provided and evaluated by the study coordinators. Replanning and resubmission was required if hard constraints were violated or soft constraints were violated more than once or with a considerable amount. This study describes the plan quality of 113 submitted EBRT dose distributions from 67 centres. Results Twenty‐four centres passed after first submission, and 23 and 10 centers needed one or more revisions, respectively. IMRT, VMAT and tomotherapy were used in 7%, 88% and 5% of the centers, and 6, 10 and 15 MV in 71%, 24% and 5% of centers, respectively. It was possible to produce acceptable plans with all techniques, energies, and treatment planning systems. The most common reasons for revisions were non‐compliant conformality index, relatively high OAR doses or insufficient lymph node coverage. Only a few (6) first submissions were rejected because of (minor) hard constraint violations. Individual feedback improved plan quality considerably (Table 1 and Figure 1) with a significant improvement of conformality index from 1.12 to 1.03. A better cooling down of the PTV edges particularly resulted in a median V43Gy reduction of 133cm 3 from first plan submission to approved plan.

Fig. 1 3D tumour contour, a single pin and the corresponding 3D modulator (upper panel); Measured vs simulated dose distributions (middle/lower panel).

Fig. 2 Measured vs. simulated X‐Z (upper/middle panel) and X‐Y (lower panel) dose distributions. Conclusion Utilizing state‐of‐the‐art 3D printing technique to manufacture complex modulators is possible. Combining the advantages of very short treatment time, the 3D range‐modulator could be an alternative to treat lung tumours with the same conformity as full raster‐scanning treatment. Further measurements must be conducted to investigate the full potential of the 3D range‐modulator. PV-100 Development of plan quality through EBRT dummy run in the EMBRACE-II study for cervical cancer Y. Seppenwoolde 1 , M. Sanggaard Assenholt 2 , D. Georg 1 , R. Nout 3 , L.T. Tan 4 , T. Rumpold 1 , A. De Leeuw 5 , I. Jürgenliemk‐Schulz 5 , C. Kirisits 1 , R. Pötter 1 , J.C. Lindegaard 2 , K. Tanderup 2 , T.E. Collaborative Group 1 1 Medical University of Vienna, Department of Radiotherapy, Wien, Austria; 2 Aarhus University