ESTRO 37 Abstract book

ESTRO 37

S605

mm) for both phantoms and both PTV sizes. The dose to the testes did not indicate a dependence on PTV margin reduction. Generally, the measured doses were higher for the large PTV compared with the small PTV. Furthermore, doses were higher for the 1-year phantom compared with the 10-year phantom, which can be explained by the organs being closer to the treatment field for a younger child. Conclusion Reduction of PTV margin from 5 mm to 3 mm resulted in a beneficial decrease in the absorbed dose to thyroid and mamma, both being highly radiosensitive organs. Therefore, the results indicate that doses from scattered and leakage radiation to those out-of-field organs can be reduced by employing a PTV margin as small as clinically acceptable. The results show that doses to organs far from the treatment field, where leakage radiation from the linac head tends to dominate, is less dependent on PTV margin size. PO-1074 Pinnacle Auto-Planning using EMBRACE II guidelines for EBRT of cervix carcinoma; clinical experience M. Groenen 1 , C. Verhagen 1 , A. Snyers 1 , C. Verhoef 1 , R. Van Leeuwen 1 1 Radboud university medical center, Radiation Oncology, Nijmegen, The Netherlands Purpose or Objective In the EMBRACE II study protocol, EBRT planning g guidelines include insights from recent studies such as the EMBRACE I study. Compared to other clinically used or study planning guidelines, the EMBRACE II study has a large number of planning objectives that are different (e.g., less strict coverage criteria for PTVs). Described is the clinical experience of Radboud University Medical Center, using the Pinnacle Auto- Planning (A-P) module an automated planning framework that facilitates and speeds up planning for the EMBRACE II protocol and gives uniform results, independent of the experience of the planner. Material and Methods Seventeen patients were planned and treated according to the EMBRACE II protocol (EBRT 25x1,8Gy to the elective PTV) using a VMAT technique, consisting of two 10MV full arcs with different collimator rotations (Elekta Agility). Using a SIB technique, nodal PTVs (PTV_Nx) were boosted to 55, 57.5 or 60 Gy. For treatment planning, Pinnacle A-P was used, (Philips, v9.10, settings in table 1). To facilitate the use of A-P, scripting was used to create help contours and to load the appropriate A-P technique and scorecard. To meet the PTV_Nx coverage criteria in the optimization, the CTV_Nx optimization goal was increased with respect to the prescribed dose (PD), while lowering the PTV_Nx–CTV_Nx optimization goal with respect to the PD. For this study, dose parameters of the most recent six patients were analyzed, thus excluding patients treated during the learning curve period.

Results Dose parameters are shown in table 2 with violated constraints indicated in red. EMBRACE II Target volume constraints were met for all patients except for the ITV45 coverage criterium (1 violation) and CTV_T_HR homogeneity criterium (4 violations). For the bladder and rectum it proved difficult to meet all constraints for all patients. Generally, a clinically acceptable plan could be obtained with a single A-P run with an additional quick optimization run or rescaling of monitor units.

Conclusion An automated planning strategy for EMBRACE II EBRT planning using Pinnacle Auto-Planning is clinically implemented. Clinically acceptable plans could be obtained with little intervention by the dose planner.