Session Item

Defining the clinical target volume (CTV) is a complex and challenging task that is traditionally owned by the radiation oncologists. Variations of CTVs drawn by different radiation oncologists for the same patient are substantial and vastly exceed the physical/technical uncertainties of targeting the radiation beam on a voxel in the patient.  Input from physicists is needed to provide a more scientific basis for CTV definition. Research and development is required along at least three different directions.  The first direction is the modeling of disease spread beyond the visible gross tumor volume, and infiltration of lymph nodes. Modeling the impact of multi-modality treatments including systemic therapies and immunotherapy, and their ability to take care of microscopic disease is also important. The second direction is to provide a probabilistic framework for CTV definition. The current binary CTV approach (100% tumor or 0% tumor) does not capture the inherent uncertainties of defining the CTV. The third and most immediate direction is to standardize current CTV definition practices based on existing clinical guidelines, by implementing them as computer algorithms in treatment planning systems.