Radiation treatment planning in brain tumours

Summary

Aim: Amino acid PET has become an important diagnostic tool for brain tumour imaging. In this data analysis, the potential impact of amino acid PET with 3-O-methyl- 6-[¹⁸F]fluoro-L-DOPA ([¹⁸F]OMFD) on radiation treatment planning is addressed by the following questions: 1. Was tumour tissue identified with OMFD-PET which was not covered by the conventionally derived planning target volume (PTV)? 2. Would the PTV have been changed incorporating OMFD-PET? Patients, methods: OMFD-PET of 25 patients after subtotal resection of malignant glioma was evaluated. The region of elevated tracer uptake of PET and of contrast enhancing masses on MRI were outlined as separate gross tumour volumes (GTV_MRI and GTV_OMFD) and reconstructed in the planning CT for comparison with the conventionally drawn GTV_conv. A PTV_new based on GTV_conv+MRI was calculated. Pairwise differential volumes were calculated to estimate overlap and differential volumes delineation by each image modality and the PTV_conv and PTV_new respectively. Results: Differential volume analysis showed > 10 cm³ of GTV_OMFD outside GTV_conv and GTV_MRI in 5/25 patients respectively. From GTV_MRI >10 cm³ were found outside GTV_OMFD in 8/25 patients. Although all tumour areas indicated by [¹⁸F]OMFD were covered by the conventionally derived PTV, based on a GTV_OMFD+MRI, the PTV_new would have been enlarged >20% in seven patients. In seven patients the PTV_new would have been reduced. Conclusion: OMFD-PET indicated tumour tissue outside the tumour region identified with MRI, adding valuable information for the delineation of the GTV in radiation treatment planning. OMFD-PET contains the potential to tailor the high dose radiation to the appropriate tumour volume, especially if dose escalation is desired.

Zusammenfassung

Ziel: Die PET mit Aminosäure-Tracern hat sich als wichtige Methode in der Hirntumordiagnostik entwickelt. In dieser Datenanalyse wurde der potenzielle Einfluss von PET mit 3-O-Methyl-6-[¹⁸F]fluor-L-DOPA ([¹⁸F]OMFD) auf die Bestrahlungsplanung anhand folgender Fragen untersucht: 1. Wurde mit OMFD-PET Hirntumorgewebe identifiziert, das nicht von dem konventionell ermittelten PTV (planning target volume) erfasst wurde? 2. Wäre das PTV unter Einbeziehung des OMFD-PET geändert worden? Patienten, Methoden: Von 25 Patienten wurden die Daten von OMFD-PET nach subtotaler Resektion von malignen Gliomen evaluiert. Die Region mit erhöhter Traceraufnahme im PET und erhöhter Kontrastmittelaufnahme im MRT wurden als separate GTV (gross tumour volume) markiert (GTV_OMFD und GTV_MRT), im Planungs-CT rekonstruiert und mit dem konventionell ermittelten GTV_conv verglichen. Ein PTV_neu basierend auf dem GTV_cov+MRT wurde berechnet. übereinstimmende und differente Volumenanteile zwischen den Bildmodalitäten bzw dem PTV_conv und PTV_neu wurden ermittelt. Ergebnisse: Die differentielle Volumenanalyse zeigte > 10 cm³ des GTV_OMFD außerhalb von GTV_conv und GTV_MRT in jeweils 5/25 Patienten. In 8/25 Patienten lag >10 cm³ des GTV_MRT außerhalb des GTV_OMFD. Wenngleich alle [¹⁸F]OMFD-positiven Regionen vom PTV_conv erfasst wurden, wäre auf der Basis von GTV_OMFD+MRT das PTV_neu in sieben Patienten um >20% vergrößert worden. In sieben Patienten wäre das PTV_neu verkleinert worden. Schlussfolgerung: OMFD-PET zeigte Tumorgewebe außerhalb der MRT-positiven Areale und liefert zusätzliche Informationen für die Bestimmung des GTV in der Strahlentherapieplanung. OMFD-PET beinhaltet als Zusatzinformation das Potential Hochdosisstrahlentherapie im adäquaten Tumorvolumen zu applizieren, besonders wenn eine Dosiseskalation angestrebt wird.

Keywords

Brain tumour - positron emission tomography - radiation treatment planning - multimodal imaging - 3-O-methyl-6-[¹⁸F]fluoro-L-DOPA

Schlüsselwörter

Hirntumor - Positronenemissionstomographie - Bestrahlungsplanung - multimodale Bildgebung - 3-O-Methyl-6-[¹⁸F]fluor-L-DOPA

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