ESTRO 2020 Abstract Book

S862 ESTRO 2020

the observation period, suggest excellent biocompatibility of the proposed marker. Conclusion We developed a novel biocompatible artifact-robust and highly visible solid fiducial marker. Although further evaluation is needed in clinical settings, our findings suggest its feasibility and benefits for implementation in kilo-voltage X-ray IGRT. PO-1588 Effect of breathing motion on robustness of locoregional proton plans for left-sided breast cancer A. Petoukhova 1,2 , L. Klaassen 2,3 , S. Habraken 2,4 , J. Jacobs 2 , M. Sattler 2,4 , K. Verhoeven 5 , Y. Klaver 2 1 Haaglanden Medical Centre, Department of Medical Physics, Leidschendam, The Netherlands ; 2 HollandPTC, Department of Radiation Oncology, Delft, The Netherlands ; 3 Delft University of Technology, Faculty of Mechanical- Maritime and Materials Engineering, Delft, The Netherlands ; 4 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands ; 5 GROW School for Oncology and Developmental Biology- Maastricht University Medical Centre, Department of Radiation Oncology MAASTRO, Maastricht, The Netherlands Purpose or Objective To investigate dosimetric impact of breathing motion on robustly optimised proton therapy treatment plans for left-sided breast cancer patients with an indication for locoregional irradiation. Material and Methods Clinical Target Volumes (CTVs) (left-sided breast, level 1 to 4 axillary, interpectoral and internal mammary lymph node (LN) regions) and organs at risk (heart, lungs and right breast) were delineated on 4D-CTs of ten female thoracic patients. CTVs of the level 1-4 axillary lymph nodes, interpectoral lymph nodes and internal mammary lymph nodes were combined in CTV elective . Two beams were used in a pencil beam scanning set-up. Beam angles were chosen to be the most favorable for each patients´ anatomy and were either a combination of 50 and 350 degrees or 0 and 45 degrees. After treatment planning to a prescribed dose of 40.05 Gy (RBE) in 15 fractions was made on the time-averaged CT, the dose was calculated with Monte Carlo on all ten phases of the breathing cycle and the robustness to setup and range errors (5mm and 3%, respectively) was evaluated for those ten phases. Correlations were evaluated between the phases of the breathing cycle and the D98% of the CTV and the D mean of the heart. Results Eight out of thirty of the correlation coefficients were statistically significant: 0.12 and -0.12 for D98% of the CTV breast of patient 2 and 7, respectively; 0.20, 0.29, 0.13 and 0.2 for D mean of the heart of four patients. At the most extreme values of the 28 robustness scenarios, the clinical goals are met for all but two patients (see Table). For the first patient, the maximum values of the D2% for the CTV elective exceeded the prescribed dose by 7.7% for all phases of the breathing cycle. For the second patient, D mean of the heart was 1.02 Gy and a strong dependence of D mean on breathing phases was observed, probably because of a large heart movement with the breathing cycle. For this patient, the amplitude of the breathing motion was 1.4 and 1.9 mm for mid-sternum and nipple, respectively. In Fig. 1, the dose distribution and the result of the robustness analysis with their correlation analyses for patient 4 , where every dot represents one scenario, are shown.

Poster: Physics track: Intra-fraction motion management

PO-1587 Novel biocompatible artifact-robust and highly visible fiducial marker for image-guided radiotherapy T. Wang 1 , N. Ikeo 2 , K. Okumura 3 , H. Akasaka 1 , R. Yada 1 , K. Yoshida 1 , D. Miyawaki 1 , T. Ishihara 1 , N. Mukumoto 1 , Y. Shimizu 1 , T. Mukai 2 , A. Nakaoka 1 , R. Sasaki 1 1 Kobe University Graduate School of Medicine, Radiation Oncology, Kobe, Japan ; 2 Kobe University, Department of Mechanical Engineering, Kobe, Japan ; 3 Kobe University Hospital, Centre for Radiology and Radiation Oncology, Kobe, Japan Purpose or Objective Develop a novel biocompatible, artifact-robust and highly visible solid fiducial marker for kilo-voltage X-ray image- guided radiation therapy (IGRT). Material and Methods The fiducial marker is made of one of the physiologically essential metal elements in the human body. An in-house phantom was designed to systematically evaluate its image artifacts (by the metal artifact index) and image visibility (by the contrast-to-noise ratio) under different conditions. Image artifacts were assessed on kilovoltage computed tomography (CT) and cone-beam CT (CBCT). The marker visibility was evaluated on two types of kilo-voltage 2D planar X-ray images from the linear accelerator. In-vivio biocompatibility characteristics, including histological and biochemical blood testing, were evaluated using the animal model of rats over 12 weeks. Results Results were compared to those from the conventional gold fiducial marker. Imaging artifacts were found dramatically suppressed by our proposed biocompatible marker compared to the gold marker (as the artifact index decreased by up to 68% in CT and by up 81% and 65% in CBCT, respectively. The visibility of the proposed marker exhibited satisfied CNRs above 2.0 for 23/32 exposures under various phantom settings, being comparable to the results of gold marker (24/32 exposures with CNRs >2.0). Further, minimal local fibrosis at the implantation site and absence of adverse effects in nearby organs over