ESTRO 2022 - Abstract Book

S1103

Abstract book

ESTRO 2022

Conclusion Higher splenic radiation doses increase the odds of severe post-CRT lymphopenia, which is common and is an independent predictor of poorer OS and higher risks of recurrence and infections in gastric cancer patients receiving adjuvant CRT. Considering the spleen as an organ-at-risk and optimizing the splenic DVH parameters before plan evaluation may decrease the risk of severe post-CRT lymphopenia.

PO-1307 High-dose stereotactic ablative body radiotherapy for locally advanced pancreatic cancer

H.I. Lee 1 , H. Kang 1 , E.K. Chie 1

1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of

Purpose or Objective To evaluate clinical outcomes of patients with locally advanced pancreatic cancer (LAPC) treated with high-dose stereotactic ablative body radiotherapy (SABR), and determine dose parameters correlated with treatment outcomes and adverse events. Materials and Methods A single institution cohort of 51 patients with LAPC treated with high-dose SABR ( ≥ 40 Gy) between 2017 and 2020 was retrospectively analyzed. Majority of the patients underwent induction chemotherapy (92.2%) for a median of 13 cycles (range, 4-29 cycles) before SABR, and had partial response in 56.9% of patients, stable disease in 19.6%, and progressive disease in 15.7%. Median prescribed dose was 50 Gy (range, 40-50 Gy) delivered in 5 fractions in all patients. Twenty-eight (54.9%) patients underwent daily adaptive SABR using magnetic resonance imaging guidance and 23 (45.1%) patients underwent linac-based non-adaptive SABR. GTV D min and GTV D max were defined as the minimum and maximum dose absorbed by 1cc of the GTV, respectively. Overall survival (OS), progression-free survival (PFS), freedom from loco-regional progression (FFLP), and freedom from distant progression (FFDP) were calculated from the start date of SABR. Results With a median follow-up of 14.6 months (range, 3.2-56.9) after SABR, the 1-year and 2-year OS rates were 71.5% (95% CI, 56.0%-82.4%) and 47.4% (95% CI 31.3%-61.9%), respectively. The 1-year and 2-year cumulative incidence of loco-regional progression were 13.2% (95% CI, 6.1%-27.2%) and 45.4% (95% CI, 29.7%-64.6%), respectively. All nine (17.6%) patients who underwent resection had R0 resection. On multivariate analysis, longer duration of induction chemotherapy (>3 months) and greater CA 19-9 decline after SABR (>50%) were associated with improved OS and PFS (all p<0.05). Response to induction chemotherapy showed significant association with PFS and FFDP (all p<0.05), and a trend toward improved OS (p=0.098). Among patients with oligometastatic cancer, response to induction chemotherapy showed a significant association with OS (p=0.009). GTV D min ≥ 50 Gy was related with significantly improved FFLP (p=0.019) and PFS (p=0.031), whereas prescribed dose and GTV D max were not. Grade 2 and 3 late toxicities occurred in 12 (23.5%) and 3 (5.9%) patients, without grade 4 or higher event. Dose to the organ at risk (D max <38 Gy and D 1cc <34 Gy) was significantly related with grade ≥ 2 late event. MRI- guided adaptive RT showed the fewer trend of grade 3 late toxicity (3.6% vs. 8.7%, p=0.398) Conclusion High-dose SABR is an effective treatment option for LAPC patients with favorable clinical outcomes and minimal interference with systemic therapy. Prospective randomized trial incorporating SABR is warranted to further elucidate the role of radiotherapy in patients with LAPC. 1 Amsterdam UMC, University of Amsterdam, Department of Radiation Oncology, Amsterdam, The Netherlands; 2 Amsterdam UMC, Vrije Universiteit Amsterdam, Department of Gastroenterology and Hepatology, Amsterdam, The Netherlands; 3 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Fiducial markers can assist in target localization during cone beam CT (CBCT) guided radiotherapy. The purpose of this study is to assess technical feasibility of fiducial marker implantation for use in pre-operative gastric cancer radiotherapy. Materials and Methods Fiducial markers were placed endoscopically in the stomach of gastric cancer patients (MaagART-01 trial, No. NL7036) prior to radiation treatment (45Gy in 25 fractions; daily CBCT imaging). Each procedure was performed under mild or deep sedation by one of four gastroenterologists. All of the currently 12 included patients received gold markers (Visicoil, Core Oncology, CA, USA; Ø 0.35mm x 10mm length), which were individually backloaded into a 22-gauge endoscopic needle prior to each placement. The last 5 patients also received liquid markers (BioXmark, Nanovi, Kongens Lyngby, Denmark; injection volume 0.08 − 0.20 mL). The liquid marker was loaded once per patient in a 25-gauge injection needle, allowing placement of multiple subsequent markers without retraction of the needle. We evaluated duration of implantation (from first loaded needle entering the endoscope to final fiducial placed) and occurrence of complications (e.g. bleeding, perforation, fever). For each marker, we determined whether (a) its implantation was assessed as successful at time of implantation (i.e., marker secured in tissue), (b) it was present on the PO-1308 Feasibility of endoscopic fiducial marker implantation in the stomach for use in image-guided RT M. Bleeker 1 , R. Pouw 2 , A. Bel 1 , J. Sonke 3 , M. Hulshof 1 , A. van der Horst 1