Description: Publication date: Available online 21 December 2016 Source: Radiotherapy and Oncology Author(s): Judith van Loon, Aniek J.G. Even, Hugo J.W.L. Aerts, Michel Öllers, Frank Hoebers, Wouter van Elmpt, Ludwig Dubois, Anne-Marie C. Dingemans, Roy I. Lalisang, Pascal Kempers, Boudewijn Brans, Véronique Winnepenninckx, Ernst-Jan Speel, Eric Thunnissen, Kim M. Smits, Ronald Boellaard, Danielle J. Vugts, Dirk De Ruysscher, Philippe Lambin Background and purpose PET imaging of cetuximab uptake may help selecting cancer patients with the highest chance of benefit. The aim of this phase I trial was to determine the safety of the tracer 89 Zr-cetuximab and to assess tumour uptake. Methods Two dose schedules were used; two consecutive doses of 60 MBq 89 Zr-cetuximab or a single dose of 120 MBq, both preceded by 400 mg/m 2 of unlabelled cetuximab. Toxicity (CTCAE 3.0) was scored twice weekly. PET-CT scans were acquired on days 4, 5 and 6 (step 1) or 5, 6, 7 (step 2). Because tumour uptake could not be assessed satisfactorily, a third step was added including EGFR overexpressing tumours. Results Nine patients were included (6 NSCLC; 3 HNC). No additional toxicity was associated with administration of 89 Zr-cetuximab compared to standard cetuximab. A tumour to blood ratio (TBR) > 1 was observed in all but one patient, with a maximum of 4.56. TBR was not different between dose schedules. There was a trend for higher TBR at intervals > 5 days after injection. Conclusions Both presented 89 Zr-cetuximab administration schedules are safe. The recommended dose for future trials is 60 MBq, with a minimum time interval for scanning of 6 days.