Two or four hour [¹⁸F]FMISO-PET in HNSCC

Summary

[¹⁸F]Fluoromisonidazole positron emission tomography (FMISO-PET) is a non invasive imaging technique that can assist detecting intra tumour regions of hypoxia. FMISO-PET evinces comparatively low signal-to-noise-ratio (SNR) and may be acquired dynamically or after different uptake times post injection (p. i.). The aim of this study was to identify, if static images acquired two hours (MISO2) or four hours (MISO4) p. i. reveal higher contrast. Patients, methods: As part of a prospective trial, 23 patients with cancers of the head and neck underwent [¹⁸F]fluoro deoxyglucose (FDG) PET before and during curative radiochemotherapy. Additionally, FMISO-PET studies 2 h and 4 h p. i. were done before treatment and after a mean dose of 11 Gy, 23 Gy and 57 Gy during RCT. After coregistration, a dedicated software was used to define the gross tumour volume (GTV) by FDG PET for the primary tumour. This volume was overlaid to the FMISO images and hypoxia within the GTV was determined. The contrast between hypoxia determined by MISO2 and by MISO4 was investigated and analysed with the Wilcoxon-matched-pairs test. Results: Mean SUV_max in tumours of all examinations was 2.2 (stdev: 0.4, min: 1.3, max: 3.4) after 2 h and 2.4 (stdev: 0.7, min: 1.1, max: 4.4) after 4 h. In the neck musculature the mean SUV_max was 1.5 at both time points and the mean SUV_mean decreased from 1.2 after 2 h to 1.1 after 4 h, respectively. These effects resulted in significantly rising contrast ratios from MISO2 to MISO4. The differently defined contrasts revealed significantly higher values for examinations 4 h p. i. (p < 0.002). Conclusion: Data acquisition of [¹⁸F]FMISO should be done 4 h p. i. to gather the optimal contrast, preferably allowing further analysis, e. g. hypoxic sub volume definition for therapy planning.

Zusammenfassung

Die [¹⁸F]Fluormisonidazol-Positronenemissionstomographie (FMISO-PET) ist ein nicht invasives Bildgebungsverfahren, das hypoxische Subvolumina in Tumoren detektieren kann. Die FMISO-PET kann dynamisch oder statisch nach unterschiedlichen Uptakezeiten post injectionem (p.i.) akquiriert werden, hat aber ein vergleichsweise niedriges Signal zu Rausch Verhältnis (SNR). Ziel dieser Studie war es für spätere Analysen zu klären, ob der Bildkontrast in statisch aufgenommenen Untersuchungen nach einer Uptakezeit von zwei Stunden (MISO2) oder vier Stunden (MISO4) p.i. höher ist. Patienten, Methoden: Bei einer Subgruppe von 23 Patienten einer prospektiven Studie zur kurativen Radiochemotherapie (RCT) von Plattenepithelkarzinomen des Hals-Nasen-Rachen-Raumes (HNSCC) wurden vor und während der Therapie [¹⁸F]Fluordeoxyglukose (FDG-)PET-Untersuchungen durchgeführt. Zusätzlich wurden bei diesen Patienten FMISO-PET-Aufnahmen zwei und vier Stunden p.i. nach Strahlentherapiedosen von im Mittel 11Gy, 23Gy und 57Gy während der RCT akquiriert. Nach Koregistrierung aller PET- und CT-Datensätze wurde die Rover-Software (ABX, Radeberg) verwendet, um das aus der FDG-PET abgeleitete „gross tumour volume” der Primärtumoren festzulegen. Diese Volumina wurden in die FMISO-Datensätze kopiert um Hypoxie innerhalb des Primärtumors zu definieren. Der Kontrast zwischen hypoxischen Regionen in den Aufnahmen MISO2 und MISO4 wurde untersucht und mit dem Wilcoxon-Rangsummen-Test auf signifikante Unterschiede geprüft. Ergebnisse: Der mittlere SUV_max der Primärtumoren aller Untersuchungen war 2.2 (stdev: 0.4, min: 1.3, max: 3.4) nach 2 h p.i. und 2.4 (stdev: 0.7, min: 1.1, max: 4.4) nach 4 h p.i.. Der mittlere SUV_max in der Nackenmuskulatur war zwei und vier Stunden p.i. 1.5 und der mittlere SUV_mean fiel von 1.2 nach 2 h auf 1.1 nach 4 h ab. Diese geringen Veränderungen bedingten aber einen steigenden Kontrast von MISO2 nach MISO4. Für die unterschiedlich definierten Kontraste ergab der Wilcoxon-Rangsummen-Test signifikant höhere Werte in den Untersuchungen vier Stunden p.i. (p < 0.002). Schlussfolgerung: Die Datenakquisition für die [¹⁸F]FMISO-PET sollte vorzugsweise vier Stunden p.i. erfolgen, da der Kontrast zwei Stunden p.i. schlechter ist. Diese Datensätze eignen sich deshalb besser für weitere Analysen, z.B.für die verbesserte Definition hypoxischer Tumorsubvolumina zur Strahlentherapieplanung.

Keywords

FMISO PET - head and neck cancer - tumour-tomuscle-ratio - contrast-to-noise-ratio - bio-imaging - radiotherapy treatment planning

Schlüsselwörter

FMISO PET - Kopf/Hals-Tumoren - Tumor-zu-Muskel-Signalverhältnis - Kontrast-zu-Rausch-Verhältnis - Bioimaging - Strahlentherapie-planung

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