PET–CT Modification of RECIST Guidelines

Extract

The World Health Organization′s 1981 criteria (1) for tumor size evaluation in response to cytotoxic treatment were simplified to the RECIST (Response Evaluation Criteria in Solid Tumors) guidelines (2) as a result of a consensus task force established in 1994. The purpose of this modification was to standardize measurements of lesion size in response to chemotherapy in adults (2,3). The RECIST guidelines were designed to allow accurate, reproducible measurements without excess time or effort. Consequently, one-dimensional measurements replaced previous two-dimensional measurements. Computed tomography (CT) provides anatomic information about the size and location of lesions. Axial CT measurements are used to assess tumor size. Positron emission tomography (PET) imaging is typically used to measure metabolic activity, which is increased in tumors. PET–CT systems have a number of advantages over CT or PET imaging alone that may allow more accurate assessment of tumor response by distinguishing scar tissue from residual tumor (4) and by facilitating easier orthogonal lesion measurements in three planes (5). Therefore, modification of RECIST guidelines to incorporate this new technology may have added benefit.