ESTRO 2020 Abstract book

S247 ESTRO 2020

sufficient follow-up who received the complete neoadjuvant sequence with SBRT is 91% (n=10/11) versus 81% for the entire cohort (n=13/16). Acute toxicity is minimal, with most patients experiencing fatigue (grade≤2: 90%) and flare-up epigastric pain (grade 1: 52%). No acute grade ≥3 gastrointestinal toxicity has been reported. Conclusion These preliminary results indicate that the integration of SIB-SBRT following multi-agent induction chemotherapy is feasible for the neoadjuvant treatment of localized PDAC. Our first analyses show favorable R0 resection rate, acute toxicity profile and 1-year OS in selected patients. PD-0421 Association of molecular profiles of pancreatic cancer with post-operative recurrence patterns X. Zhu 1 , C. Yangsen 1 , Y. Yusheng 1 , J. Xiaoping 1 , Z. Xianzhi 1 , J. Lingong 1 , G. Lei 1 , S. Yuxin 1 , Q. Shuiwang 1 , C. Fei 1 , J. Zhen 1 , F. Fang 1 , Z. Houjun 1 1 Changhai Hospital, Radiation Oncology, Shanghai, China Purpose or Objective The consensus of radiotherapy of target volumes delineations after pancreaticoduodenectomy were uniform expansions of 1cm on regions of interest (ROI) and identical in all patients and without considerations of molecular profiling. This study was to identify recurrence patterns of pancreatic adenocarcinoma with different molecular profiles after surgery and a proper radiation dose to recurrences, for the individualized treatment plan design. Material and Methods Patients with pathologically confirmed resectable pancreatic ductal adenocarcinoma were included. Stereotactic body radiation therapy was delivered to recurrent lesions. All surgical specimens underwent immunohistochemical staining of Ki-67, P53 and PD-L1. Local recurrences were plotted with respect to the celiac axis (CA) and superior mesenteric artery (SMA) on one computed tomographic scan of a template patient. Results There were 116, 152 and 170 patients with the signal intensity of Ki-67 of ≤10%, 11%-49% and ≥50%, respectively. Furthermore, the signal intensity of P53 of ≤10%, 11%-49% and ≥50% was found in 261, 79 and 98 patients, respectively. Due to recent clinical practice of immunotherapy, PD-L1 was only tested in 89 patients, with 68 and 21 having the expression level of PD-L1 of TC0 and IC0 and TC1/2 or IC1/2. With the increasing intensity of Ki- 67, the mean distance from the superior board of the recurrent lesion to the CA (P<0.001), the inferior board to the SMA (P<0.001), the posterior board to the CA (P<0.001) and SMA (P<0.001) significantly increased. Similarly, with the increasing intensity of P53, the mean distance from the superior board of recurrence to the CA (P<0.001), the inferior board to the SMA (P=0.012), the anterior board to the SMA (P=0.013), the posterior board to the CA (P=0.043) increased. Regarding the increasing level of PD-L1, only a significant increase of the mean distance from the superior board of recurrence to the CA was found (P=0.011). Survival benefits were found in patients with all levels of Ki-67, P53 and PD-L1 receiving a BED beyond 65Gy for recurences.

Table 1. Distance between the different boards of 80% recurrences to the vessels

Distance between the superior board of 80% recurren ces and the CA

Distance between the inferior board of 80% recurren ces and the SMA

Distance between the posterior board of 80% recurren ces and the CA

Distance between the posterior board of 80% recurren ces and the SMA

Distance between the anterior board of 80% recurren ces and the SMA

Ki-67 ≤10 % 11%-

10.1mm 9.4mm 9.2mm 9.4mm ---

10.3mm 9.7mm 10.0mm 10.3mm ---

49%

≥50

13.8mm 9.9mm 11.0mm 11.0mm ---

%

P53

≤10

9.7mm 9.7mm 10.1mm ---

8.9mm

%

11%-

11.8mm 9.5mm 10.2mm ---

9.4mm

49%

≥50

13.2mm 9.9mm 10.6mm ---

9.6mm

%

PD- L1

TC0

and IC0

10.9mm ---

---

---

---

TC1 /2 or IC1/2

13.5mm ---

---

---

---

Conclusion Regarding higher intensities of Ki-67, P53 and higher levels of PD-L1, a non-uniform expansion, 14-15mm and 10- 11mm superiorly on the CA and inferiorly on the SMA, may be required. A higher dose for recurrences may be beneficial for improved survival in the case of patients' well tolerance. PD-0422 Evaluating inter-observer variation in oesophageal target volume delineation O. Nicholas 1 , G. Lewis 2 , B. Thomas 3 , M. Smyth 2 , E. Spezi 4 , S.H. Gwynne 1 1 Swansea Bay University Health Board, South West Wales Cancer Centre, Swansea, United Kingdom ; 2 Velindre University NHS Trust, Departmenf of Physics- Velindre Cancer Centre, Cardiff, United Kingdom ; 3 Velindre University NHS Trust, Department of Oncology- Velindre Cancer Centre, Cardiff, United Kingdom ; 4 Cardiff University, School of Engineering, Cardiff, United Kingdom Purpose or Objective Inter-observer variation in target volume delineation (TVD) is the most significant source of uncertainty in radiotherapy (RT). Variation in TVD can have a negative impact on survival. For clinical trials, RTQA is an essential component of delivering safe and effective RT by ensuring adherence to trial protocols. In the UK there have been two recent major clinical trials involving neoadjuvant RT in oesophageal cancer; the NeoSCOPE and Neo-AEGIS