Application of functional imaging to radiotherapy (RT) is a rapidly expanding field with the development of new modalities and techniques. Functional imaging of PET in conjunction with RT provides new avenues towards the clinical application of dose painting-a new RT strategy delivering optimized dose redistribution according to the functional imaging information to further improve tumor control. Two prototypical strategies of dose painting are reviewed: dose painting by contours (DPBC) and dose painting by numbers (DPBN). DPBN set a linear correlation of the boost dose and image intensity of this same voxel while homogeneous dose is given to the subvolume contoured by a threshold created in PET images in DPBC. Both comply strict organs at risk (OAR) constraints and are alternatives for boosting subvolumes in clinical practice.This review focuses on the rationale, target validation, dose prescription verification and evaluation and recent clinical achievements in the field of integrating PET imaging into RT treatment planning. Further research is necessary in order to investigate unresolved problems in its routine clinical application thoroughly.

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