Abstract

Radiation oncology is a rapidly evolving specialty. In analogy with the evolution from conventional radiotherapy over 3D conformal radiotherapy to intensity modulated radiotherapy and volumetric modulated arc therapy there has been a shift from the use of anatomical imaging (e.g. CT, MR) to functional imaging (e.g. DW-MRI, DCE-MRI) and biological imaging (e.g. 18F-FDG PET). In the current process of radiation treatment, the radiobiological response of tumor and normal tissue in patients is monitored non-invasively by a variety of imaging techniques. Integration of these imaging techniques into therapy selection strategies and radiation treatment can serve several purposes. First, pre-treatment assessments can steer decisions on the radiation treatment as such or on the combination with other modalities. Second, biology-based objective functions can be introduced into the radiation treatment planning process by coregistration of molecular imaging. Relevant radiobiological parameters that can be assessed include tumour burden, tumour hypoxia, tumour proliferation and tumour metabolism. This would allow us to generate customized heterogeneous dose distributions with escalated doses to tumour areas where radiotherapy resistance mechanisms are most prevalent. However, there are some hurdles to overcome including the discrepancy between resolution of imaging techniques and spatial scale at which radiosensitivity is determined and the treatment induced temporal and spatial changes in tumor morphology and biology. Third, monitoring of temporal and spatial variations in these radiotherapy resistance mechanisms early during the course of treatment can discriminate responders from nonresponders. With such information available shortly after the start of treatment, modifications can be implemented or the radiation treatment plan can be adapted based on the biological response pattern. In this teaching lecture, some background on the different imaging techniques at our disposal for early response monitoring wil be given and examples of current applications and future prospectives for the further integration of imaging in the radiation treatment process will be shown.

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