ESTRO 2023 - Abstract Book

S88

Saturday 13 May

ESTRO 2023

Conclusion IMPT treatment of esophageal cancer can be performed in a robust manner, resulting in sufficient target coverage over the treatment course. Adaptation to correct for underdosage of the ITV appears to be most effective in the 1st week of treatment. Diaphragm baseline shifts, heart water equivalent depth, and weight loss are predictive factors for ITV under dosage, and should be incorporated in an adaptation protocol. OC-0126 Linac-based pancreatic SABR using combined triggered imaging with auto beam hold and CBCTs A. Miovecz 1,2,3 , K. Kisivan 1 , D. Erdelyesi 1 , D. Gutyina 1 , C. Glavak 1 , G. Lukacs 4 , K. Mahr 5 , A. Gulyban 6 , Z. Kaposztas 7 , F. Lakosi 1,2 1 Moritz Kaposi General Hospital, Dr. Jozsef Baka Center, Department of Radiation Oncology, Kaposvar, Hungary; 2 University of Pécs, Faculty of Health Sciences, Department of Medical Imaging, Kaposvar, Hungary; 3 University of Pécs, Faculty of Health Sciences, Doctoral School of Health Sciences, Pécs, Hungary; 4 Moritz Kaposi General Hospital, Department of Oncology, Kaposvar, Hungary; 5 Zala County Hospital Szent Rafael, Department of Oncology, Zalaegerszeg, Hungary; 6 Institut Jules Bordet, Medical Physics Department, Bruxelles, Belgium; 7 Moritz Kaposi General Hospital, Department of Surgery, Kaposvar, Hungary Purpose or Objective To demonstrate our clinical experiences with linac-based stereotactic ablative radiotherapy (SABR) using triggered imaging (TI) and auto-beam hold (ABH) for locally advanced pancreatic cancer (LAPC). Materials and Methods Between 2016 and 2021 patients with LAPC treated with induction chemotherapy (iCT) followed by VMAT-based SABR were included. ITV-based(5), phase-gated(5) or deep-inspiration breath-hold(DIBH,4) techniques were used. Treatment verification started with 3D/4D CBCTs followed by intrafractional TI+ABH using intraoperatively placed peritumoral surgical clips(10), bile duct stent(3), lipiodol(1). In case of ≥ 3mm deviations, delivery was interrupted for correction using additional imaging (2D/3D match±CBCT) or a gating threshold adjustment. A post-RT CBCT was done for the verification of residual errors and OARs. Post-RT CBCT verification was performed using (half-arc) Spotlight mode for time efficiency. Beam interruptions and treatment time were recorded. The Krippendorff's- α coefficient ( α≥ 0.8) was used to determine the agreement among 5 radiation therapists (RTT) in 4 LAPC cases (40 CBCTs) about the OARs positions relative to planning risk volume (PRV) on both pre-and post-DIBH-CBCTs. Progression free survival (PFS) and overall survival (OS) were assessed by the Kaplan-Meier analysis and reported both from start of iCT and end of SABR. Acute and late toxicity were scored using CTCAEv4. Results Fourteen LAPC patients were analyzed. Gemcitabine (29%) or Folfirinox (71%) iCT regimens were given. The median treatment time was 19±11 min. with significantly shorter time span with DIBH-SABR compared to phase-gated ones (19.9±6.2 vs. 30±13.4, p<0.01). On average, beams were interrupted once (range: 0-3) per treatment sessions. Based on the reviews of individual RTTs DIBH-CBCT can be used to reliably determine OARs position relative to PRV [Krippendorff- α =0.85 (0.71 1)], independently from CBCT acquisition type. In two pts offline treatment adaptations were made due to substantial volume- and positional changes of the stomach. The median OS/PFSiCT were 20 and 12 months, while OS/PFSSABR were 15