Functional imaging for evaluation of cancers and biologically conformal radiotherapy: Past-history and present-day perspectives.

Over the past twenty years, nuclear medicine has enhanced the role of functional imaging in cancerology. A major milestone was achieved in the early 2000s with widespread availability of the positron emitter tracer 18F- deoxyglucose (FDG) and the introduction of hybrid imagers, i.e. positron imagers coupled with an X CT, providing anatomical landmarks and potently contributing to attenuation and scatter correction of the images. Other technical advances have progressively increased the quality of positron images. To date, the most widely used tracer remains FDG, which is highly beneficial in terms of sensitivity and specificity in detection of tumor sites, also providing biological information on tumors and early evaluation of treatment response for most cancers. Other highly specific tracers have been developed and are now routinely used for pheochromocytoma and paraganglioma, neuroendocrine tumors, and prostate cancer.

Biological Radiotherapy has two aspects: Internal radiotherapy consisting in administration of a tumor-specific molecule radiolabeled with an isotope delivering an adequate radiation dose to the targeted tumor sites (on the model of thyroid cancer treated with radioiodine) and external radiotherapy designed to determine tumor volume, assess response and to dose radiation according to the tumor characteristics shown by functional imaging.