In actuality, tumors do not necessarily grow symmetrically different portions may grow at different rates ( 5). While RECIST has been promoted as a simple and practical one-dimensional measurement approach that provides more reproducible results than the World Health Organization method, both criteria suffer from several limitations ( 2), including the assumptions that tumor size changes in a symmetric fashion, that tumor volume is simply related to a planar measurement, and that four discrete categories of volume change are sufficient to quantify disease response or progression.
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RECIST is an update to the 1979 World Health Organization method ( 4), which relied on two-dimensional measures achieved by multiplying a tumor's maximum diameter in the transverse plane by its largest perpendicular diameter on the same image.
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Similarly, short-term knowledge of tumor response is needed to make patient-specific therapy decisions to give the best possible clinical outcome.Ĭurrently, nodule size is typically evaluated by comparing the maximum diameter of a nodule on serial scans in accordance with the Response Evaluation Criteria in Solid Tumors (RECIST) ( 2, 3), which place nodule response in one of four categories: complete response, partial response, stable disease, and disease progression. Such small changes in size are difficult to recognize visually, particularly when nodules are irregular in shape. A nodule of that size will have doubled in volume when it measures 6.3 mm in diameter. Nodules as small as 5 mm (about 65 mm 3 in volume) may require short-term follow up in as little as 3–6 months.
The time interval depends on the specific clinical circumstance some lung cancers, particularly adenocarcinomas, are more aggressive than others and may spread outside the thorax and become systemically disseminated, even when the primary tumor is small. Size measurements need to be accurate and consistent to enable assessment of nodule change in a short time interval. Lung nodule measurements made with computed tomography (CT) are used in clinical practice to assess size change estimated from serial scans obtained over time to predict the likelihood of malignancy ( 1) and to monitor the response of tumor to treatment ( 2). Understanding and quantifying the sources of volumetric measurement error in the assessment of lung nodules with CT would be a first step toward the development of methods to minimize that error through system improvements and to correctly account for any remaining error. The review points to the need for continued research to examine volumetric accuracy as a function of a multitude of interrelated variables involved in the assessment of lung nodules. The need for public databases of phantom scans, as well as of clinical data, is discussed. A number of underexamined areas of research regarding volumetric accuracy are identified, including the measurement of nonsolid nodules, the effects of pitch and section overlap, and the effect of respiratory motion. The purpose of this article is to provide a review of published studies relevant to the computed tomographic (CT) volumetric analysis of lung nodules. Volume measurement precision and accuracy depend on a number of factors, including image-acquisition and reconstruction parameters, nodule characteristics, and the performance of algorithms for nodule segmentation and volume estimation.
Lung nodule volumetry is used for nodule diagnosis, as well as for monitoring tumor response to therapy.