ESTRO 36 Abstract Book

S438 ESTRO 36 2017 _______________________________________________________________________________________________

Germany 2 German Cancer Consortium DKTK, Partner Site Freiburg, Freiburg, Germany 3 Medical Center University of Freiburg - Faculty of Medicine - University of Freiburg, Department of Radiation Oncology, Freiburg, Germany 4 Medical Center University of Freiburg - Faculty of Medicine - University of Freiburg, Department of Pathology, Freiburg, Germany 5 Medical Center University of Freiburg - Faculty of Medicine - University of Freiburg, Department of Nuclear Medicine, Freiburg, Germany 6 University of North Carolina, Department of Radiation Oncology, North Carolina, USA 7 Karolinska Institutet - Stockholm University, Department of Medical Radiation Physics, Stockholm, Sweden Purpose or Objective The goal of this work is to show the technical feasibility and to evaluate the normal tissue complication probability (NTCP) and the tumor control probability (TCP) of the intensity modulated radiation therapy (IMRT) dose painting technique using 68 Ga-HBED-CC PSMA-PET/CT in patients with primary prostate cancer (PCa). Material and Methods We studied 10 RT plans of PCa patients having PSMA- PET/CT scans prior to radical prostatectomy. One contour was semi automatically generated for each patient on the basis of the 30% of SUVmax within the prostate (GTV-PET). For each patient, two IMRT plans were generated: PLAN 77 , which consisted of whole-prostate radiation therapy to 77 Gy in 2.2 Gy per fraction; PLAN 95 , which consisted of whole-prostate RT to 77 Gy in 2.2 Gy per fraction, and a simultaneous integrated boost to the GTV-PET to 95 Gy in 2.71 Gy per fraction. The feasibility of these plans was judged by their ability to reach prescription doses while adhering to the FLAME trial protocol. Comparisons of TCPs based on co-registered histology after prostatectomy (TCP-histo) and normal tissue complication probabilities (NTCP) for rectum and bladder were carried out between the plans. Results Prescription doses were reached for all patients plans while adhering to dose constraints. The mean doses on GTV-histo for [Plan 77 and Plan 95 ] were 75.8±0.3 Gy and 96.9±1 Gy, respectively. In addition, TCP-histo values for Plan 77 and Plan 95 were 70±7 %, and 95.7±2 %, respectively. PLAN 95 had significantly higher TCP-histo (p<0.0001) values than PLAN 77 . There were no significant differences in rectal (p=0.563) and bladder (p=0.3) NTCPs between IMRT dose painting for primary PCa using 68 Ga-HBED-CC PSMA-PET/CT was technically feasible. A dose escalation on GTV-PET resulted in significantly higher TCPs without higher NTCPs. PO-0825 Multi-scenario sampling in robust proton therapy treatment planning E. Sterpin 1 , A. Barragan 2 , K. Souris 2 , J. Lee 2 1 KU Leuven, Department of Oncology, Leuven, Belgium 2 Université catholique de Louvain, Molecular imaging- radiotherapy and oncology, Brussels, Belgium Purpose or Objective Beam specific PTVs (BSPTV) or robust optimizers are superior to conventional PTVs for ensuring robustness of proton therapy treatments. In these planning strategies, realizations ('scenarios”) of a few types of uncertainties are simulated: errors in patient setup, CT HU conversion to stopping powers, and, more recently, breathing motion. However, baseline shifts of mobile targets should also be taken into account, which complicates the sampling of the space of possible scenarios. We compare the 2 plans. Conclusion

influence matrix). After solving the optimization problems, the optimal fluence map is imported back to Eclipse for leaf sequencing and final dose calculation using the Eclipse API. The entire workflow is automated, requiring user interaction solely to prepare the contours and beam arrangement prior to launching the HCO Eclipse API plugin. Optimization requires ~1-3 hours, after which the automated plan including final dose calculation is ready in Eclipse. Results HCO IMRT automatic planning was tested for 10 patients with spinal lesions who had previously been treated to 24 Gy in a single fraction using either VMAT (8 patients) or multi-field IMRT (2 patients). All automated HCO plans used multi-field IMRT. A typical automated and clinical plan comparison is shown in Figure 1, demonstrating improved PTV coverage, cord and esophagus sparing with the automated plan. As shown in Table 1, on average, the automated plan improved PTV coverage (V95%) by 1%, cord maximum dose by 2%, cord D0.35cc by 12%, cauda maximum dose by 15%, and esophagus V18Gy by 100%. All HCO plans met all clinical planning criteria. Table-1. Comparison of clinical and HCO automated plans for ten patients. For each criterion, the better score is bolded.

Figure-1. Comparison of the clinical and automated plans for a patient. A1-A3 represent the automated plan and C1- C3 represent the clinical plan. Conclusion Hierarchical constrained optimization shows promise as a powerful tool to automate IMRT treatment planning. The automated treatment plan meets all clinical criteria and compares favorably in relevant metrics to the plan generated by planners. Using Eclipse API, we developed a plugin which fully automates the workflow and can be implemented into clinical use after thorough testing.

Poster: Physics track: Treatment planning: applications

PO-0824 IMRT dose painting for prostate cancer using PSMA-PET/CT: a planning study based on histology K. Koubar 1,2 , C. Zamboglou 2,3 , I. Sachpazidis 1,2 , R. Wiehle 1,2 , S. Kirste 2,3 , V. Drendel 2,4 , M. Mix 2,5 , F. Schiller 2,5 , P. Mavroidis 6,7 , P.T. Meyer 2,5 , A.L. Grosu 2,3 , D. Baltas 1,2 1 Medical Center University of Freiburg - Faculty of Medicine - University of Freiburg, Division of Medical Physics - Department of Radiation Oncology, Freiburg,