PET/Computed Tomography in Treatment Response Assessment in Cancer: An Overview with Emphasis on the Evolving Role in Response Evaluation to Immunotherapy and Radiation Therapy.

The effectiveness of cancer treatment must be assessed early in the course of the therapy so that regimens can be tailored in an individualized manner. Whole-body metabolic burden, metabolic tumor volume and total lesion glycolysis are the newer quantitative PET metrics that reflect the overall disease burden and take into account the stage of the disease, the heterogeneous intra-tumoral metabolism and uptake of PET tracer. Immunotherapy response evaluation in solid tumors is challenging, and combined use of anatomical and molecular imaging could evolve as the optimal way for assessing treatment response to immunotherapy. PET based parameters may be better predictors of response, necrosis and recurrence of disease after radiation therapy vis-à-vis the conventional cross-sectional imaging.