ESTRO 2023 - Abstract Book

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ESTRO 2023

patients received involved field irradiation (IFI). The rates of in-field and out-field locoregional failure were 23.6% and 3.6% for ENI and 10.3% and 5.1% for IFI group, respectively, showing no significant difference. There were more grade 3 ESCC patients (P=0.089) and patients treated with chemotherapy (P<0.001) in the ENI group. After the propensity score matching, there were still no significant difference between the ENI and IFI patients in the failure patterns. In the multivariate analysis among T1b patients, no clinicopathologic factors, including RT field, RT dose, RT technique, concurrent chemotherapy use, tumor grade, and tumor multiplicity were associated with the survival outcomes listed above. After the propensity score matching, concurrent chemotherapy use was associated with favorable locoregional recurrence free survival (Hazard ratio, 0.25; P=0.036) and progression free survival (HR, 0.23; P=0.026). 10 (10.6%) patients experienced grade ≥ 3 adverse events.

All patients % (n=138)

cT1a % (n=20)

cT1b % (n=94)

cT1x % (n=24)

Failure sites

Total

24.6 (34) 30.0 (6) 24.5 (23) 20.8 (5)

Locoregional 22.5 (31) 25.0 (5) 22.3 (21) 20.8 (5) Infield Locoregional 18.8 (26) 25.0 (5) 18.1 (17) 16.7 (4) Outfield locoregional 3.6 (5) 0.0 (0) 4.3 (4) 4.2 (1) Distant metastasis 5.1 (7) 5.0 (1) 6.4 (6) 0.0 (0)

Conclusion cT1a patients who cannot receive endoscopic resection, showed similar rates of failure compared with cT1b patients, which questioned the accuracy of the staging and raised the need for aggressive treatment such as chemoradiotherapy. In cT1b patients, IFI with concurrent chemotherapy could be a reasonable treatment option.

PO-1391 Dose intensification in Locally Advanced Pancreatic Cancer using Robotic SBRT

M. valzano 1 , M. Loi 1 , P. Bonomo 1 , L. Masi 2 , R. Doro 2 , V. Salvestrini 2 , M. Banini 1 , V. Lorenzetti 1 , I. Morelli 1 , A. Romei 1 , V. Di Cataldo 1 , G. Francolini 1 , D. Greto 1 , M. Mangoni 1 , G. Simontacchi 1 , L. Livi 1 1 Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Radiation Oncology, Firenze, Italy; 2 Istituto Fiorentino di Cura e Assistenza (IFCA), CyberKnife Center, Firenze, Italy Purpose or Objective Radiotherapy in locally advanced pancreatic cancer (LAPC) has been proposed as a consolidative local treatment after induction chemotherapy in stable disease, or as a primary treatment in patients unfit to either surgery or chemotherapy. It has been proposed that improved local response may be obtained if a Biologically Effective Dose (BED10, assuming α / β =10 Gy) of 100 Gy is delivered to the tumor. We investigated the use of robotic SBRT, with real-time tumor tracking, to a prescribed dose of 50 Gy in 5 fractions (BED10=100 Gy) in a cohort of LAPC patients. Materials and Methods We conducted a retrospective review of LAPC patients treated with robotic SBRT at our institution from May 2021 to October 2022. Planning aim was to cover ≥ 93% of the GTV with ≥ 95%(V47.5) of the target dose (50 Gy in 5 fractions) and 95% of the PTV with 95%(V38) of the target dose (40 Gy in 5 fractions). Dose constraints to Organs at Risk (OAR) were prioritized over target dose objectives. Mandatory constraint for dose-limiting OARs (duodenum, stomach, bowel) were V35 ≤ 0.5cc and V25 ≤ 10cc. Real-time tumor tracking was implemented following endoscopic ultrasound-guided fiducial marker placement. Toxicity was reported according to CTCAE v 5.1 scale. Results Ten patients were included in our analysis. Two patients received exclusive irradiation, while 8 patients underwent SBRT as a local consolidation after obtaining stable disease/partial response following induction chemotherapy with different regimens: Nab-paclitaxel and Gemcitabine for 2 patients; Gemcitabine for 1 patient; FOLFIRINOX for 4 patients; FOLFOX for 1 patient. Median GTV was 45.0 (10.6-81.4) cc. The median number of implanted fiducials for each SBRT treatment was 2 (range 1-2). Planning aim was achieved in 6 cases. The median GTV (47.5Gy) and PTV(38Gy) coverage was 94.1% (range 79.9 – 100%) and 95,8% (range 92.1– 100%) respectively. Median V35 was 0.14 (range 0.0 – 0.49), 0.10 (range 0.0 – 0.5), and 0.25 (range 0.0 – 0.49) cc for duodenum, stomach and bowel respectively. Median V25 was 4.3 (range 0.0 – 7.97), 1.86 (range 0.0 – 7.78), and 5.63 (range 1.8 – 10.0) cc for duodenum, stomach and bowel respectively (Fig.1).