Linac-based pancreatic SABR using combined triggered imaging with auto beam hold and CBCTs
OC-0126
Abstract
Linac-based pancreatic SABR using combined triggered imaging with auto beam hold and CBCTs
Authors: Adam Miovecz1,2,3, Katalin Kisivan1, Dora Erdelyesi1, David Gutyina1, Csaba Glavak1, Gabor Lukacs4, Karoly Mahr5, Akos Gulyban6, Zsolt Kaposztas7, Ferenc Lakosi1,2
1Moritz Kaposi General Hospital, Dr. Jozsef Baka Center, Department of Radiation Oncology, Kaposvar, Hungary; 2University of Pécs, Faculty of Health Sciences, Department of Medical Imaging, Kaposvar, Hungary; 3University of Pécs, Faculty of Health Sciences, Doctoral School of Health Sciences, Pécs, Hungary; 4Moritz Kaposi General Hospital, Department of Oncology, Kaposvar, Hungary; 5Zala County Hospital Szent Rafael, Department of Oncology, Zalaegerszeg, Hungary; 6Institut Jules Bordet, Medical Physics Department, Bruxelles, Belgium; 7Moritz Kaposi General Hospital, Department of Surgery, Kaposvar, Hungary
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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).
Material 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 and 8 months, respectively. Five (36%) patient reached exceptional long tumor control (22-41 months (iCT), 18-32 months (SABR), two of them are still alive without any sign of progression. The dominant pattern of failure was distant metastasis (12/14). There was no Gr. ≥2 acute/late RT-related toxicity.
Conclusion
Linac-based pancreatic SABR with TI+ABH is feasible. Peritumoral fiducials improves utility, while DIBH-CBCT -preferably with half arc- provides the best image quality at a reasonable treatment time. The clinical efficacy is comparable with the literature, showing durable tumor control and favorable survival besides negligible RT side effect.