ABSTRACT
This chapter reviews the response assessment after the completion of therapy, as well as during treatment. Adaptive radiation therapy started to adapt to setup errors and intrafraction motion. After treatment response assessment with positron emission tomography (PET) was developed a first trial assessing the feasibility of PET-guided adaptive treatment was conducted. Quality of life during-treatment assessments could be used similarly to organs-at-risk and tumor during-treatment assessment for adaptive treatment. Metabolic tumor response assessment using fludeoxyglucose (FDG)-PET is a powerful tool measuring and predicting treatment response. FDG-PET can also successfully predict the onset of esophagitis with a median time to onset of 11.6 days after PET and an area under the curve of 0.84. Comparing computed tomography (CT) and FDG-PET during treatment after two-thirds of treatment were completed, a reduction of metabolic tumor volume of 70% was observed while gross tumor volume assessed by CT was reduced only by 41%.
