ESTRO 2022 - Abstract Book

S1456

Abstract book

ESTRO 2022

patients, a total amount of 460 automated plans (AP) for different radiation therapy techniques were generated by the use of the “Plan Explorer” auto planning module (RaySearch Laboratories, Stockholm, Sweden). Clinical objectives were checked for the selected AP candidates and evaluated against the respective clinical manual plan (MP) created in the “Raystation” TPS that were taken as base line. Plan evaluations considered selected dosimetric plan parameters. Target coverage, homogeneity index (HI), conformity index (CI), organs at risk sparing, efficiency of design and planned delivered times were compared between MP and APs. Quality assurance of MP and AP was performed in order to evaluate the dosimetric accuracy of automatically generated VMAT plans. Results The lexicographic optimization-based algorithm implemented in Plan Explorer was able to produce plans of clinical quality, meeting target coverage objectives and organs at risk constraints for a random cohort of prostate cancer patients. With equivalent Target Planning Volume (PTV) V95%, D98% , Dmax% , HI and CI, significant improvements in organ at risk (OARs) sparing of the rectum, bladder and intestine were obtained, with mean dose reductions for AP of 4.5% (Range: 7.1% - 2.7%); 3.5% (Range: 5.1% - 1.2%) and 2.7 % (Range: 5.3 – 0.2), respectively, for the mean-organ-dose parameter. Significant differences in the average number of monitor units (MU) were found between MP and AP, depending on the radiation therapy technique. Therefore delivery times can be reduced considering clinical criteria. Not only overall active plan design time for AP was reduced by 55% with respect to MP, but, in addition, resources for AP optimizations could be used outside of normal working hours, allowing to increase production and optimize resource use. Conclusion Plan Explorer can automatically generate acceptable clinical treatment plans for prostate cancer with either improved or similar results compared to manually created plans. Time reduction in plan design as well as human & computational resources optimization improves clinical efficiency. Purpose or Objective Immobilization with an open face mask is more comfortable and less invasive than frame-based immobilization during radiosurgery, but concerns about intra-fraction motion must be addressed, particularly when treating multiple brain metastases with a single isocenter. The online setup control with surface gating has been shown to improve the safety of SRS treatments. We developed an institutional protocol, evaluated the accuracy of the patient setup, and analyzed the impact of setup uncertainties on the dose distribution, PTV coverage and OAR sparing. Materials and Methods Fifteen patients treated in a single fraction and single isocenter for multiple brain metastases (2 to 8 lesions) were included in this study. The VMAT-plans were calculated with Varian HyperArc and delivered on a TrueBeam clinac equipped with an optical surface monitoring system (OSMS, Align-RT, Vision-RT). The patients were fixed with an open face mask on a dedicated board (QFix Encompass), the same immobilization setup was used for MR-imaging directly after the CT- simulation. A GTV to PTV margin of 2 mm was used for contouring. The prescribed dose was 18 to 20 Gy at the encompassing 80%-isodose. The patients were initially set up according to the displacement shown by the OSMS, the positioning was then adjusted by IGRT. Patient positioning was controlled online, using as baseline a reference surface acquired immediately after the setup- CBCT. If the real time shifts detected be the OSMS exceeded 1mm/1°, the beam was automatically stopped and IGRT- repositioning was performed. The real time shifts were recorded during the entire treatment. Finally, an end-CBCT was acquired. The planning-CT was shifted and rotated according to the displacements detected by the end-CBCT and the HyperArc plan was recalculated on the displaced planning-CT. Results The displacement shown by the OSMS during the initial patient positioning correlated very well to the setup CBCT shifts (translations 0.6 ± 0.4 mm, rotations 0.5 ± 0.3°). The OSMS-detected real time shifts did not show a significant dependence on the couch rotation, with a trend towards bigger shifts for couch angle 90°/270°. The average shifts between the setup- CBCT and the end-CBCT were 0.3 mm / 0.3° (with a maximum shift of 1.1 mm / 1.2° for one patient). The recalculated plans showed for all patients a GTV coverage ≥ 99.5%. The average PTV volume encompassed by the prescribed isodose was 94% (worst coverage 90% for the outlier patient). No relevant difference in the OAR-dose was observed. Conclusion Surface gating allows a safe delivery of HyperArc treatments of multiple brain metastases with a single isocenter, if the tolerances for the online monitoring are sufficiently small. The clinical outcome will be assessed in a longer follow-up. PO-1658 Frameless Surface-Gated Single-Isocenter Radiosurgery: Setup Accuracy and Plan Robustness S. Puccini 1 , M. Hoeft 1 , U. Großmann 1 , J. Halbur 1 , D. Völzke 1 , R. Semrau 1 , H. Rief 1 1 Strahlentherapie Bonn-Rhein-Sieg, ,, Bonn - Troisdorf - Euskirchen, Germany

PO-1659 Participation in clinical trials improved harmonization of dosimetric parameters applied in SBRT

M. Josipovic 1 , M. van Overeem Felter 2 , W. Ottosson 2 , E. Worm 3 , H. Sand 4 , M. Nielsen 5 , T. Bjørn Nielsen 5 , R. Slot Thing 6 , G. Fredberg Persson 2 1 Copenhagen University Hospital - Rigshospitalet, Dept. of Oncology, Copenhagen, Denmark; 2 Copenhagen University Hospital - Herlev and Gentofte, Dept. of Oncology, Copenhagen, Denmark; 3 Århus University Hospital, Dept. of Oncology, Aarhus, Denmark; 4 Aalborg University Hospital, Dept. of Medical physics, Dept. of Oncology, Aalborg, Denmark; 5 Odense