ESTRO 2021 Abstract Book

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ESTRO 2021

slabs (from CIRS) and in real tissues (animal experiment); 3) Clinical commissioning consisting in the retrospective analysis of more than 100 clinical treatments, considering Single Field Optimization (SFO) and Multiple Field Optimization (MFO) plans. myQAiON was compared both to mPSQA in water and to the TPS in patient CT geometry. Gamma index criteria were evaluated and defined for different treatment locations. Results The proton beam model was found to be well within clinical tolerances. Differences to our commissioning data were within 0.2 mm in range, 5% in beam size and 1% in dose, considering more than 40 boxes in water. The calculated WET agreed within 4% with the TPS (Table 1). Outliers were found for lung and bone tissues against the experimental results (-11% and +8.8%, respectively). Clinical commissioning results in water were similar to the TPS. Clinical commissioning in patient CT geometry allowed defining the gamma criteria 2%/2mm for almost all clinical CT protocols, except for Abdomen where 3%/3mm was used instead. No difference between SFO and MFO beams was found. The retrospective analysis of more than 100 treatments is presented in Figure 1. Based on these results, we defined the gamma index pass rate of 95% as a warning level and 90% as a fail level.

Conclusion myQAiON was successfully commissioned and implemented for horizontal proton beam lines. mPSQA is substituted by IDC for at least 25% of the cases since 1/2/2021. mPSQA will be further reduced up to 50% in

the upcoming year, thus allowing more machine time for patient treatment. [1] Jhonson et al, PLOS ONE 2019, https://doi.org/10.1371/journal.pone.0212412

PH-0598 Variance-based sensitivity analysis of inter-observer, range and setup variability in proton therapy J. Hofmaier 1 , F. Walter 1 , I. Hadi 1 , M. Rottler 2 , R. von Bestenbostel 1 , G. Dedes 3 , K. Parodi 3 , M. Niyazi 4 , C. Belka 4 , F. Kamp 4 1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 2 University Hospital, LMU Munich, Department of Radiation Oncology , Munich, Germany , Germany; 3 Faculty of Physics, LMU Munich, Department of Medical Physics, Munich, Germany; 4 University Hospital, LMU Munich, Department of Radiation Oncology , Munich, Germany Purpose or Objective Margin concepts in proton therapy aim to cover the clinical target volume (CTV) in presence of setup (SU) and range uncertainties (RU). Due to inter-observer variability (IOV), the CTV itself is uncertain. We evaluated the combined impact of IOV, SU and RU in a variance-based sensitivity analysis (SA). Materials and Methods For 10 patients with skull base meningioma, CTVs were contoured independently by 4 clinicians using PET and MR imaging (CTV obs ). No GTV-to-CTV margin was applied. As “ground truth”, consensus CTV structures (CTV s ) were generated using the simultaneous truth and performance level estimation algorithm. PTVs were derived for each CTV obs using beam specific margins (6mm distal, 5mm proximal, 3mm lateral). For each PTV, a proton