Correspondence to: Patrick Therasse, MD, EORTC Data Center, Avenue E, Mounier 83/11, B-1200, Brussels, Belgium (e-mail: pth{at}eortc.be)
OConnell addressed two different issues that have been and still are the focus of specific research programs. The first issue is the use of three-dimensional measurement to assess tumor volume and response. These measurements can be made with most modern computed tomography (CT) machines and do not require a positron emission tomographycomputed tomography (PETCT) machine. To date, the added value of a three-dimensional approach used in the context of tumor response evaluation has not been proven to bring additional information that would alter the decision taken at the end of a trial. The second issue is the use of PET scans to measure tumor response. As OConnell indicates, this tool can certainly be useful to differentiate scar tissue from residual tumor tissue after treatment, but this can be done with PET scan alone. Also, objective quantification of the tumor response in terms of metabolic activity remains mostly unvalidated to date.
Although we can recognize the advantages of using a PETCT machine instead of two separate machines (and examinations), we dont see that there is any added information generated by PETCT systems in tumor response evaluation compared with either standard PET or CT examinations alone. However, the author is right when he says that we will have to take this new imaging technique into account for future revision of the RECIST (Response Evaluation Criteria in Solid Tumors) guidelines.
NOTES
Dr. Otto Hoekstra (Department of Nuclear Medicine, Free University Hospital, Amsterdam) and Dr. Frédéric Lecouvet (Department of Radiology, St. Luc University, Brussels) contributed to this discussion.
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