The application of functional imaging techniques to personalise chemoradiotherapy in upper gastrointestinal malignancies

Abstract

Functional imaging gives information about physiological heterogeneity in tumours. The utility of functional imaging tests in providing predictive and prognostic information after chemoradiotherapy for both oesophageal cancer and pancreatic cancer will be reviewed. The benefit of incorporating functional imaging into radiotherapy planning is also evaluated. In cancers of the upper gastrointestinal tract, the vast majority of functional imaging studies have used (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET). Few studies in locally advanced pancreatic cancer have investigated the utility of functional imaging in risk-stratifying patients or aiding target volume definition. Certain themes from the oesophageal data emerge, including the need for a multiparametric assessment of functional images and the added value of response assessment rather than relying on single time point measures. The sensitivity and specificity of FDG-PET to predict treatment response and survival are not currently high enough to inform treatment decisions. This suggests that a multimodal, multiparametric approach may be required. FDG-PET improves target volume definition in oesophageal cancer by improving the accuracy of tumour length definition and by improving the nodal staging of patients. The ideal functional imaging test would accurately identify patients who are unlikely to achieve a pathological complete response after chemoradiotherapy and would aid the delineation of a biological target volume that could be used for treatment intensification. The current limitations of published studies prevent integrating imaging-derived parameters into decision making on an individual patient basis. These limitations should inform future trial design in oesophageal and pancreatic cancers.

Keywords: Functional imaging; oesophageal cancer; pancreatic cancer; radiotherapy treatment planning; response assessment; target volume delineation.

Fig 1

Magnified view of a trans-axial section through a locally advanced pancreatic adenocarcinoma. The gross tumour volume (GTV; red) was agreed by two radiation oncologists using only the planning contrast enhanced CT (CECT). Following registration with ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET), it can be seen that FDG-avid tissue extends beyond the GTV. A semi-automated process can produce volumes outlined by 40% of the maximum standardised uptake value (SUV_max; blue) or 50% of the SUV_max, which may facilitate accurate GTV definition.

Fig 2

Axial image from ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) in a patient with locally advanced pancreatic cancer. An FDG-avid peripancreatic node that was not identified at the time of diagnostic CECT was detected and included in gross tumour volume definition at the time of radiotherapy planning.

Fig 3

Axial images from ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) in a patient with locally advanced pancreatic cancer. Although FDG avidity can be used to inform target volume definition, the process cannot be fully automated. FDG-uptake can be seen to correspond with a mass within the pancreatic head (A). This area of avidity runs the length of the stent within the common bile duct, including areas beyond that of the tumour mass (B). FDG avidity is also associated with inflammatory cell glucose metabolism.