Predicting and evaluating response to therapy may become one of the most important indications for FDG-PET in oncology. The FDG-PET result could serve as a surrogate for actual patient outcomes in clinical practice and in drug development. The FDG-PET end result can be qualitative or, increasingly often, quantitative.

In this context, three methodological aspects of a totally different nature are of crucial importance: getting the right numbers out of the scan (standardization, validation of simplified quantitative measures), validating the biological relevance of the tracer signal (changes), and developing and validating the response criteria. In this chapter, examples of each of these domains (physics, biology, and epidemiology) will be discussed. To some extent, the cases have been modified from actual practice for didactical reasons.

A 62-year-old female with locally advanced cancer of the left breast was treated with experimental neoadjuvant chemotherapy. No data have been published on FDG-PET and this new therapeutic agent. A secondary aim of the study is to explore the use of FDG-PET to evaluate the response to this therapy.

Acquisition and processing parameters and findings

Dynamic FDG-PET scans were obtained at baseline and after one cycle of therapy. The PET scanner (ECAT EXACT HR+; Siemens/CTI, Knoxville) used provides an axial field of view of 15.5 cmand produces 63 transaxial slices with a slice thickness of 2.5mm. The patient fasted for at least 6 hours prior to the imaging sessions. The patient was scanned in the supine position with arms at her sides. The patient was positioned in such a way that the dominant lesions were in the center of the field of view.