Tumour hypoxia imaging with 18 F-fluoroazomycinarabino- furanoside PET/CT in patients with locally advanced rectal cancer Birgitte M. Havelund a,d , Paw C. Holdgaard b , Søren R. Rafaelsen c , Lise S. Mortensen e , Jørn Theil f , Dirk Bender f , John Pløen a , Karen-Lise G. Spindler a,d and Anders Jakobsen a,d Objective The aim of this study was to investigate the feasibility of 18 F-fluoroazomycinarabinofuranoside ( 18 F-FAZA) positron emission tomography (PET)/ computed tomography (CT) in patients with locally advanced rectal cancer. Materials and methods The study included 14 patients with locally advanced rectal cancer. Before chemoradiotherapy, PET/CT with 18 F-FAZA was performed with static 15 min images 2 h after injection of 18 F-FAZA. Attenuation correction was obtained with a low-dose CT, and a contrast-enhanced CT was performed immediately after the PET scan. Results 18 F-FAZA uptake [mean and maximum standardized uptake value (SUV mean ) and (SUV max )] was significantly higher in rectal tumours than in both muscles (P < 0.003) and normal intestinal walls (P <5 ¾ 10 –5 ). The tumour to muscle (T/M) ratios ranged from 1.19 to 3.05 with a mean of 1.97, whereas the tumour to intestinal wall (T/I) ratios had values of 1.73–5.81 with a mean of 2.83. Intense activity accumulating in the bladder produced obvious scattered activity, which spread into the surrounding tissue. Tumour volumes excluding scatter were therefore determined, in which the SUV max and SUV mean were also significantly higher than in both muscles (P< 0.004) and normal intestinal walls (P <2 ¾ 10 –5 ) and had T/M ratios of 1.19–2.72 with a mean of 1.85 and T/I ratios of 1.71–5.40 with a mean of 2.67. The individual SUV max , SUV mean , T/M and T/I values were significantly higher in the entire tumour volume compared with the tumour volume adjusted for scatter from the urinary bladder (P < 0.005), although the absolute differences were small. Conclusion 18 F-FAZA PET/CT is feasible for visualization of hypoxia in patients with rectal cancer, but scattered activity from the urinary bladder should be taken into consideration. Nucl Med Commun 34:155–161  c 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins. Nuclear Medicine Communications 2013, 34:155–161 Keywords: 18 F-fluoroazomycinarabinofuranoside, hypoxia, imaging, PET, radiotherapy, rectal neoplasm Departments of a Oncology, b Nuclear Medicine, c Radiology, Vejle Hospital, Vejle, d Institute of Regional Health Services Research, University of Southern Denmark, Odense, Departments of e Experimental Clinical Oncology and f Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, Aarhus C, Denmark Correspondence to Birgitte Mayland Havelund, Department of Oncology, Vejle Hospital, Kabbeltoft 25, 7100 Vejle, Denmark Tel: +45 794 06038; fax: +45 794 06907; e-mail: birgitte.mayland.havelund@slb.regionsyddanmark.dk Received 12 July 2012 Revised 27 August 2012 Accepted 24 October 2012 Introduction The standard treatment of locally advanced rectal cancer is long-course chemoradiotherapy (CRT) followed by surgery based on total mesorectal excision. Preoperative CRT reduces the risk of local recurrence, but the individual response to CRT varies [1]. A minor group of patients will experience complete tumour response verified by pathological examination of the surgical specimens and may therefore be candidates for watchful waiting without surgery [2,3]. A better method for selecting these patients is thus of prime importance. Tumour hypoxia is an acknowledged phenomenon in the development of malignant tumours [4], and hypoxia- associated radiotherapy (RT) resistance has been known for decades [5]. The clinical importance of hypoxia in relation to RT is best established in squamous cell carcinoma of the head and neck, in which tumour hypoxia is linked to poor survival after RT [6]. Tumour hypoxia has been identified in adenocarcinomas of the rec- tum [7,8], but the role of hypoxia in relation to CRT for rectal cancer remains to be determined. Previously, direct measurement of the oxygen tension in the tumour using a polarographic ‘Eppendorf ’ needle electrode was considered the gold standard method for measuring hypoxia [9]. Another commonly used method is injection of nitromidazole derivates (e.g. pimonidazole) and subsequent immunohistochemical visualization in the resected tumour or in biopsies [9]. Noninvasive measurement of hypoxia by PET scans using hypoxia-specific tracers is attractive because of the Data were presented at the ESMO 14th World Congress on Gastrointestinal Cancer (June 27–30, 2012), and have been published as an abstract in Ann Oncol 2012; 23(Suppl 4) ( 18 F-FAZA in rectal cancer, abstract no. P-0298). Original article 0143-3636  c 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/MNM.0b013e32835bd5bc Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.