PD-L1 PET Imaging During Neoadjuvant (Chemo)Radiotherapy in Esophageal and Rectal Cancer

50 Gy in 2 Gy fractions over 25 working days + capecitabine 1650 mg/m2/d PO

25 Gy in 5 Gy fractions over 5 working days

41.4 Gy in 1.8 Gy fractions over 23 working days + carboplatin AUC of 2 mg/ml/min + paclitaxel 50 mg/m2 IV Q1W

10 mg atezolizumab IV followed by 37 MBq 89Zr-atezolizumab IV. PET imaging will be done before neoadjuvant CRT/SCPRT (day 0) and between day 10-14 during CRT/SCPRT.