| The integration of FDG-PET functional data into conventional anatomically-based GTV delineation may lead to optimization of dose to biological target volumes in radiotherapy. We are proposing a method for uncovering tumor sub-volumes using functional data. For a cohort of 27 histo-pathologically proven non-small cell lung carcinoma patients, background uptake values were sampled over slices containing tumor within contra-lateral healthy lung and then scaled by the ratio of tissue densities between healthy lung and tumor. Signal-to-background uptake values within volumes of interest encompassing the tumor were scored from which differential uptake volume histograms were constructed. These were subsequently decomposed into the minimum number of analytical functions that yielded acceptable net fits, as assessed by chi.;2values. For our patient population, at least four sub-volumes over the sampled volume of interest consistently evolved. It is possible that sub-volume thresholds may be extracted from custom-made differential uptake volume histograms for individual patients and then subsequently used for delineation of biological target volumes. At this point, however, we can only make a hypothesis that crossing point of the second and third fitted peak of the uptake volume histogram may help in singling out necrotic tissue, while the crossing point between third and fourth fitting function may help in identification of the glycolytic sub-volume within the tumor. Extensive pre-clinical studies are needed to establish correlation between these sub-volumes and their true underlying physiology. |
