Biological imaging in radiation oncology

The goal of this study was to discuss the value of integrating biological imaging (PET, SPECT, MRS etc.) in radiation treatment planning and monitoring. Studies in patients with brain tumors have shown that, compared to CT and MRI alone, the image fusion of CT/MRI and amino acid SPECT or PET allows a more correct delineation of gross tumor volume (GTV) and planning target volume (PTV). For FDG-PET, comparable results with different techniques are reported in the literature also for bronchial carcinoma, ear-nose-and-throat tumors, and cervical carcinoma, or, in the case of MRS, for prostate cancer. Imaging of hypoxia, cell proliferation, apoptosis, tumor angiogenesis, and gene expression leads to the identification of differently aggressive areas of a biologically inhomogeneous tumor mass that can be individually and more appropriately targeted using innovative IMRT. Thus, a biological, inhomogeneous dose distribution can be generated, the so-called dose painting. In addition, the biological imaging can play a significant role in the evaluation of the therapy response after radiochemotherapy. Clinical studies in ear-nose-and-throat tumors, bronchial carcinoma, esophagus carcinoma, and cervical carcinoma suggest that the sensitivity and specificity of FDG-PET for the therapy response are higher compared to anatomical imaging (CT and MRI). Clinical and experimental studies are required to define the real impact of these investigations in radiation treatment planning, and especially in the evaluation of therapy response.