Adapting dose prescription to tumour heterogeneities: The impact of the functional contrast

Tumours are heterogeneous structures. The evolution of functional imaging techniques and the use of new tracers for PET images allow characterizing tumour heterogeneities in terms of clonogenic cell density, partial oxygen pressure or proliferation. Within this context, the basic idea is to prescribe PET-based non uniform dose distributions in order to improve treatment outcome. Two scenarios can be considered to adapt treatment to tumour heterogeneities: namely the dose boosting or the dose redistribution. In the first case a sub-volume within the tumour will receive a higher dose, while in the second scenario the mean dose is kept equal to the clinical uniform dose but is redistributed within the tumour compartments considered. A dose redistribution based on maximisation of the tumour control probability (TCP) under constraint was considered. A number of FDG and FMISO PET simulated datasets considering different tumour shapes and heterogeneities and two clinical cases were used in this study. For each case six contrasts were considered in order to analyse the impact of the functional contrast on dose calculation and treatment outcome calculated with TCP. For all contrasts considered there is only a small benefit using dose redistribution with FDG-PET (TCP increase <; 3%) but a high benefit with FMISO-PET images (TCP increase >; 5%). For the dose boosting scenario the TCP increase is higher (up to 7% and 55% for a 5Gy boost applied to FDG and FMISO PET resp.).