ESTRO 2023 - Abstract Book

S1118

Digital Posters

ESTRO 2023

Conclusion Liver SBRT in breath-hold using SGRT and prolonged breath-holds by NHFT is feasible for the majority of patients. Breath holding resulted in high-quality CBCT imaging (Figure 2) that showed breath-hold variations smaller than the PTV margin. However, to further decrease the PTV, internal anatomy-based inter- and intra-breath-hold monitoring is desired.

PO-1389 Prediction of daily GI doses in SBRT for pancreatic cancers using the shortest distance to GTV.

Y. Uchinami 1 , T. Kanehira 2 , K. Nakazato 2 , Y. Fujita 1 , S. Takahashi 1 , H. Taguchi 3 , K. Kobashi 4 , N. Katoh 1 , K. Takahashi 5 , H. Aoyama 6 , N. Miyamoto 2 , K. Yokokawa 2 1 Hokkaido University Faculty of Medicine and Graduate School of Medicine, Department of Radiation Oncology, Sapporo, Japan; 2 Hokkaido University Hospital, Department of Medical Physics, Sapporo, Japan; 3 Hokkaido University Hospital, Department of Radiation Oncology, Sapporo, Japan; 4 Hokkaido University Faculty of Medicine and Graduate School of Medicine, Global Center for Biomedical Science and Engineering, Sapporo, Japan; 5 Hokkaido University Graduate School of Medicine, Department of Biostatistics, Sapporo, Japan; 6 Hokkaido University Faculty of Medicine and Graduate School of Medicine, Department of Radiation Oncology,, Sapporo, Japan Purpose or Objective Stereotactic body radiotherapy (SBRT) for pancreatic cancers is expected to improve treatment outcomes, but dose uncertainty due to inter-fractional motion should be considered. This study aims to verify whether the daily gastrointestinal tract (GI-tract) doses can be predicted based on the shortest distance between gross tumor volume (GTV) and GI-tract. Materials and Methods The analyzed cases included ten pancreatic cancer patients receiving a fiducial-based respiratory-gated SBRT of 40 Gy in 5 fractions. The planning CT was scanned at the natural expiration, and the SBRT plan was generated by step-and-shoot intensity-modulated radiotherapy (IMRT) with 9-10 portals. Here, we defined this reference treatment plan as PLANref. Before every fraction, CT images for dose evaluation were obtained at the same position and respiratory phase as in the planning CT. Using PLANref, the dose was evaluated by re-calculating PLANref on the daily CT with the same positional relationship between the isocenter and the fiducial marker. We also defined the re-calculated evaluation plan as PLANeval. The three-dimensional shortest distance was calculated from GTV to each GI-tract (gastro-duodenum, small intestine, and large intestine) using a commercially available MIM maestro ver. 7.0 (MIM Software, Cleveland, OH, USA). The institutional dose constraint is volume receiving 33 Gy (V33) < 0.5 cm3 for the planning at risk volume (PRV) of each organ, which was