Hypoxia is a cause of resistance to radiotherapy, especially in patients with head and neck squamous cell carcinoma (HNSCC). The purpose of this study was to evaluate (18)F-fluoroazomycin arabinoside (FAZA) positron emission tomography (PET)/computed tomography (CT) hypoxia imaging as a prognostic factor in HNSCC patients receiving radiotherapy. Forty patients with HNSCC treated with radiotherapy (66-76 Gy) were included. Static FAZA PET/CT imaging 2h post injection was conducted prior to irradiation. The hypoxic volume (HV) was delineated using a tumor-to-muscle value ≥ 1.4. In 13 patients, a repetitive FAZA PET/CT scan was conducted during the radiotherapy treatment. A hypoxic volume could be identified in 25 (63%) of the 40 tumors. FAZA PET HV varied considerably with a range from 0.0 to 30.9 (median: 0.3) cm(3). The T(max)/M(med) ranged from 1.1 to 2.9 (median: 1.5). The distribution of hypoxia among the Human Papillomavirus (HPV) positive (12/16) and negative (13/24) tumors was not significant different. In the FAZA PET/CT scans performed during radiotherapy, hypoxia could be detected in six of the 13 patients. For these six patients the location of HV remained stable in location during radiotherapy treatment, though the size of the HV decreased. In 30 patients a positive correlation was detected between maximum FAZA uptake in the primary tumor and the lymph node. During a median follow up of 19 months a significant difference in disease free survival rate with 93% for patients with non hypoxic tumors and 60% for patients with hypoxic tumors could be detected. This study emphasizes the role of FAZA PET/CT imaging as a suitable assay with prognostic potential for detection of hypoxia in HNSCC.

LET-painting was suggested as a method to overcome tumour hypoxia. In vitro experiments have demonstrated a well-established relationship between the oxygen enhancement ratio (OER) and linear energy transfer (LET), where OER approaches unity for high-LET values. However, high-LET radiation also increases the risk for side effects in normal tissue. LET-painting attempts to restrict high-LET radiation to compartments that are found to be hypoxic, while applying lower LET radiation to normoxic tissues. Methods. Carbon-12 and oxygen-16 ion treatment plans with four fields and with homogeneous dose in the target volume, are applied on an oropharyngeal cancer case with an identified hypoxic entity within the tumour. The target dose is optimised to achieve a tumour control probability (TCP) of 95% when assuming a fully normoxic tissue. Using the same primary particle energy fluence needed for this plan, TCP is recalculated for three cases assuming hypoxia: first, redistributing LET to match the hypoxic structure (LET-painting). Second, plans are recalculated for varying hypoxic tumour volume in order to investigate the threshold volume where TCP can be established. Finally, a slight dose boost (5-20%) is additionally allowed in the hypoxic subvolume to assess its impact on TCP. Results. LET-painting with carbon-12 ions can only achieve tumour control for hypoxic subvolumes smaller than 0.5 cm(3). Using oxygen-16 ions, tumour control can be achieved for tumours with hypoxic subvolumes of up to 1 or 2 cm(3). Tumour control can be achieved for tumours with even larger hypoxic subvolumes, if a slight dose boost is allowed in combination with LET-painting. Conclusion. Our findings clearly indicate that a substantial increase in tumour control can be achieved when applying the LET-painting concept using oxygen-16 ions on hypoxic tumours, ideally with a slight dose boost.

Introduction. Polarographic oxygen-sensitive electrodes have demonstrated prognostic significance of hypoxia. However, its routine application is limited. ¹⁸F-FMISO PET scans are a noninvasive approach, able to measure spatial and temporal changes in hypoxia. The aim of this study was to examine the association between measures of hypoxia defined by functional imaging and Eppendorf pO₂ electrodes. Materials and methods. A total of 18 patients were included, nine squamous cell carcinoma of the head and neck and nine soft tissue tumors. The tumor volume was defined by CT, MRI, ¹⁸FDG-PET or by clinical examination. The oxygenation status of the tumors was assessed using ¹⁸F-FMISO PET imaging followed by Eppendorf pO₂ electrode measurements. Data were compared in a ‘virtual voxel’, resulting in individual histograms from each tumor. Results. The percentages of pO₂ ≤ 5 mmHg ranged from 9 to 94% (median 43%) for all 18 tumors. For ¹⁸F-FMISO PET the T/M ratio ranged from 0.70 to 2.38 (median 1.13). Analyzing the virtual voxel histograms tumors could be categorized in three groups: Well oxygenated tumors with no hypoxia and concordance between the ¹⁸F-FMISO data and the Eppendorf measurements, hypoxic tumors likewise with concordance between the two assays and inconclusive tumors with no concordance between the assays. Conclusion. This study analyzed the relationship between ¹⁸F-FMISO PET and Eppendorf pO₂ electrode measurements by use of a virtual voxel model. There was a spectrum of hypoxia among tumors that can be detected by both assays. However no correlation was observed, and in general tumors were more hypoxic based on Eppendorf pO₂ measurements as compared to ¹⁸F-FMISO PET.

Background: In head and neck squamous cell carcinomas (HNSCC) hypoxic radioresistance can be reduced by use of the hypoxic modifier nimorazole, as shown in the DAHANCA 5 trial. Recently, a 15-gene hypoxia classifier has shown predictive impact for the effect of nimorazole by identifying ‘more’ and ‘less’ hypoxic tumors in the DAHANCA 5 cohort. A prospective multicentre EORTC-1219 study is initiated, where nimorazole and prospective use of the classifier as a predictor is tested in relation to the most recent accelerated chemoradiotherapy treatment. Validation of the gene expression classification procedures is described here. Material and methods: Formalin-fixed paraffin-embedded (FFPE) tumor material from three recent HNSCC cohorts [DAHANCA 18 (n = 96), 24 (n = 40), and IAEA Hypo (n = 55)] was used to establish and validate procedures for prospective classification of patients. Repeatability was tested for the different steps in the gene expression analysis, and reproducibility was tested with xenograft tumors (FaDu_DD, UTSCC33), where gene expression in complementary sections was compared after fixation and embedding locally and at international institutions, respectively. Intra-tumor heterogeneity was addressed by classifying biopsy samples from HNSCC tumors, where 2–4 biopsies from each tumor was accessible. Results: Procedures were successfully established for individual classification of HNSCC patients in retrospective and prospective cohorts. Measurements of gene expression levels were reproducible between different international institutions. Conclusion: Technical validation of the 15-gene hypoxia classifier demonstrated that it is suitable for implementation in prospective clinical trials.