ESTRO 2022 - Abstract Book

S1104

Abstract book

ESTRO 2022

first scan post-implantation (pre-treatment CT or first CBCT (on reconstructed CBCT or projection images)) and (c) it was present on the last fraction’s CBCT. Finally, we assessed adequacy of location, i.e. in or near the stomach wall. Results In total, we attempted to implant 79 markers (5 − 8 per patient; 61 Visicoil and 18 BioXmark; Fig 1). Duration of implantation was 16 − 38 min (mean=24 min), implantation time per marker was 2.5 − 5.4 min (mean=3.7 min). There were no procedure- related complications. At time of implantation, 68 markers were assessed to be implanted successfully (Fig 2). When markers were assessed as not successful at time of implantation (all Visicoil), this was mostly due to either technical difficulties (e.g. unable to push marker out of needle), or incomplete implantation caused by peristaltic motion. On the first scan post-implantation, 65 markers were present. Of those, 59 were still present on the last fraction’s CBCT, 4 disappeared prior to radiation treatment (within 1 − 10 days post-implantation), and 2 disappeared during treatment (15 and 22 days post-implantation; fractions 5 and 8). Four markers (all Visicoil) were not placed correctly: one in diaphragm, one in spleen, and two in fatty tissue >1 cm from the stomach. For the markers that remained full treatment, no migration was observed. Conclusion Fiducial marker placement in the stomach was technically feasible and successful, for both Visicoil (38 of 61 attempts, 62%) and BioXmark (17 of 18, 94%). Visibility and benefit of fiducial markers in image-guided radiotherapy (using 4DCT and 4DCBCT) will be evaluated in an ongoing study.