Abstract
Background and purpose
Positron-emission tomography (PET) with [18F]-fluoromisonidazole (FMISO) permits consideration of radiotherapy dose escalation to hypoxic volumes in head and neck cancers (HNC). However, the definition of FMISO volumes remains problematic. The aims of this study are to confirm that delayed acquisition at 4 h is most appropriate for FMISO-PET imaging and to assess different methods of volume segmentation.
Patients and methods
A total of 15 HNC patients underwent several FMISO-PET/computed tomography (CT) acquisitions 2, 3 and 4 h after FMISO injection. Three automatic methods of PET image segmentation were tested: fixed threshold, adaptive threshold based on the ratio between tumour-derived and background activities (RT/B) and the fuzzy locally adaptive Bayesian (FLAB) method. The hypoxic fraction (HF), which is defined as the ratio between the FMISO and CT volumes, was also calculated.
Results
The RT/B for images acquired at 2, 3 and 4 h differed significantly, with mean values of 2.5 (1.7–2.9), 3 (2–4.5) and 3.4 (2.3–6.1), respectively. The mean tumour volume, as defined manually using CT images, was 39.1 ml (1.2–116 ml). After 4 h, the mean FMISO volumes were 18.9 (0.1–81), 9.5 (0.9–33.1) and 12.5 ml (0.9–38.4 ml) with fixed threshold, adaptive threshold and the FLAB method, respectively; median HF values were 0.47 (0.1–1.93), 0.25 (0.11–0.75) and 0.35 (0.14–1.05), respectively. FMISO volumes were significantly different.
Conclusion
The best contrast is obtained at the 4-hour acquisition time. Large discrepancies were found between the three tested methods of volume segmentation.
Zusammenfassung
Hintergrund und Ziel
Die Positronenemissionstomographie (PET) mit [18F]-Fluoromisonidazol (FMISO) ermöglicht in der Strahlentherapie für Kopf-Hals-Tumore (KHT) eine Dosissteigerung auf hypoxische Volumina. Allerdings bleibt die Bestimmung der FMISO-Volumina problematisch. Ziel dieser Studie ist es, verschiedene Volumen-Segmentierungsmethoden zu beurteilen und zu bestätigen, dass eine verzögerte Aufnahme von 4 h das Beste für die FMISO-PET-Bildgebung ist.
Patienten und Methoden
Insgesamt 15 KHT-Patienten unterzogen sich mehreren Aufnahmen einer FMISO-PET/Computertomographie (CT) jeweils 2, 3 und 4 h nach FMISO-Injektion. Es wurden drei automatische Segmentierungsmethoden von PET-Bildern getestet: ein fester Schwellenwert, ein adaptiver Schwellenwert, basierend auf dem Verhältnis zwischen den tumorösen und den Hintergrundaktivitäten (VT/H), sowie die „fuzzy-locally-adaptive-bayesian“-(FLAB-)Methode. Die hypoxische Fraktion (HF), die als das Verhältnis zwischen dem FMISO-Volumen und dem CT-Volumen definiert ist, wurde ebenfalls berechnet.
Ergebnisse
Die VT/H für Bilderaufnahmen nach 2, 3 und 4 h unterschieden sich mit einer mittleren Wert von jeweils 2,5 (1,7–2,9), 3 (2–4,5) und 3,4 (2,3–6,1) signifikant. Das mittlere, manuell mittels CT definierte Tumorvolumen betrug 39,1 ml (1,2–116). Nach 4 h ergaben sich mittlere FMISO-Volumina und eine mittlere HF von jeweils 18,9 ml (0,1–81) und 0,47 (0,1–1,93) mit dem festen Schwellenwert, 9,5 ml (0,9–33,1) und 0,25 (0,11–0,75) mit dem adaptiven Schwellenwert sowie 12,5 ml (0,9–38,4) und 0,35 (0,14–1,05) mit der FLAB-Methode. Die FMISO-Volumina waren signifikant unterschiedlich.
Schlussfolgerung
Den besten Kontrast erhält man bei der 4-Stunden-Aufnahme. Zwischen den drei getesteten Segmentierungsverfahren wurden große Unterschiede festgestellt.
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Funding
No funding was received for this study.
Acknowledgements
The authors thank Pippa McKelvie-Sebileau for medical editorial assistance in English.
Compliance with ethical guidelines
Conflict of interest. B. Henriques de Figueiredo, T. Merlin, H. de Clermont-Gallerande, M. Hatt, D. Vimont, P. Fernandez and F. Lamare state that there are no conflicts of interest.
All studies on humans described in the present manuscript were carried out with the approval of the responsible ethics committee and in accordance with national law and the Helsinki Declaration of 1975 (in its current, revised form). Informed consent was obtained from all patients included in studies.
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Henriques de Figueiredo, B., Merlin, T., de Clermont-Gallerande, H. et al. Potential of [18F]-Fluoromisonidazole positron-emission tomography for radiotherapy planning in head and neck squamous cell carcinomas. Strahlenther Onkol 189, 1015–1019 (2013). https://doi.org/10.1007/s00066-013-0454-7
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DOI: https://doi.org/10.1007/s00066-013-0454-7