Content area
Full Text
Eur J Nucl Med Mol Imaging (2007) 34:15631565 DOI 10.1007/s00259-007-0487-1
EDITORIAL COMMENTARY
Imaging of tumour hypoxia using PET and 18F-labelled tracers: biology meets technology
Tove Grnroos & Heikki Minn
Published online: 28 June 2007 # Springer-Verlag 2007
One current major goal in non-invasive nuclear imaging of cancer is prediction of the fractional hypoxic volume, i.e. the proportion of hypoxic cells within a solid tumour. Hypoxic cells in both rodent and human tumours are about threefold more resistant to radiation therapy than their well-oxygenated counterparts [1], and there is also strong evidence to link hypoxia with malignant progression leading to increased invasive potential and metastasis [2]. Ever since the discovery that 2-nitroimidazole-based compounds bind to cellular macromolecules under a low oxygen concentration [3], attempts have been made to utilise this chemical property to design a probe capable of external imaging of hypoxic tumour cells. Such a probe is desired by the radiotherapy community to help overcome the limited success in clinical trials in which tumour oxygenation has been targeted. One might assume that detection of hypoxic tumours with functional imaging will lead to a therapeutic gain through the use of methods permitting selective cell kill in poorly oxygenated regions within a larger tumour volume [4, 5].
The development of nitromidazole derivatives and thiosemicarbazone ligands labelled with short-lived radio-nuclides, such as 123I(T1/2=13.3 h), 64Cu (T1/2=12.7 h) and
18F(T1/2=109.8 min), as tools for hypoxia imaging utilising SPECT and PET has been a major task during recent decades [6]. With the advent of integrated PET and CT scanners featuring full radiation therapy planning capability, it is obvious that PET tracers in particular will receive much attention in the near future. The key issue is the ability to translate the volumetric information from a functional imaging study to the treatment planning system. In this context, both scanner resolution and target-to-background uptake ratio are important, since quantitation of hypoxia-specific radionuclide uptake is relevant for optimisation of intensity-modulated radiotherapy (IMRT). Inverse planning IMRT utilises a so-called dose painting by numbers technique, which assumes that small irregular volumes inside a tumour should receive a higher than standard photon dose to control hypoxic and radioresistant cells [7]. Combining IMRT with planning PET/CT using a hypoxia-avid tracer is an attractive but as yet unproven method...