ESTRO 2021 Abstract Book

S1574

ESTRO 2021

from Mirada Medical Ltd. Results

In figure 1, the left graph shows motion difference between Mid-P estimates compared to: rigid registration, 4DCT GTV contour motion, and landmarks. The right graph shows PTV margins based on motion estimates[2] from the two Mid-P methods and GTV contours. Motion differences range from 0-2mm and when converted to margins differ by <0.2mm.

Figure 2 shows box plots of voxel intensity within a GTV contour thresholded at -300HU for the two Mid-P and BH images. Asterisks indicate that voxel intensities belong to different distributions according to the Kruskal-Wallis test (p<0.05). For four patients there are no statistical differences between the three scans. In one patient observed variations are within the range of variations between individual 4DCT phases. Conclusion The experiments described can effectively assess a Mid-P implementation against independent measures of breathing motion from a 4DCT scan and BH image. The two tested implementations produced similar outputs. Defining pass/fail criteria for any Mid-P implementation based on these experiments is ongoing. This work is funded by Eurostars grant E!113263. [1] Wolthaus, J. et al https://doi.org/10.1016/j.ijrobp.2007.11.042 [2] van Herk, M., P. Remeijer and J. V. Lebesque. https://doi.org/10.1016/S0360-3016(00)00518-6 [3] Vandemeulebroucke, J. et al. The POPI-model a point-validated pixel-based breathing thorax model ICCR, 2007 Purpose or Objective This study attempts to explore a novel lung stereotactic body radiotherapy (SBRT) planning technology that can balance the advantages and disadvantages of conformational radiotherapy (CRT) and intensity modulated radiotherapy (IMRT) / volumetric modulated arc therapy (VMAT) in Pinnacle Treatment Planning System (TPS). Materials and Methods This study retrospectively analyzed the treatment plans of twenty peripheral lung cancer patients who underwent SBRT in our center. For each of the patients, treatment plans were designed based on planning methods including CRT, IMRT, VMRT and the proposed CRT-IMRT-combined (Co-CRIM) planning techinique using Pinnacle TPS, respectively. In the Co-CRIM technique, an inverse optimization algorithm was applied, and the number of subfields in each field was limited to one. The minimum subfield area was set to the size of the GTV, and the minimum MU of the subfield was the quotient obtained through dividing fractional dose by twice the total number of fields. The performance of Co-CRIM was evaluated through the comparisons of various dosimetric parameters of planning target volume (PTV) and organs at risk (OARs), monitor units (MU), plan verification pass rate γ, and planning time with CRT, IMRT and VMAT. PO-1847 A novel CRT-IMRT-combined (Co-CRIM) planning technique for peripheral lung SBRT Y. Duan 1 , Z. Xu 1 1 Shanghai Chest Hospital, Shanghai Jiaotong university, Shanghai, China