Thoracic Imaging 2003 - Society of Thoracic Radiology

Reporting Tumor Measurements in Oncologic Imaging
Todd R. Hazelton, M.D.
Assistant Professor of Radiology and Oncology
H. Lee Moffitt Cancer Center and Research Institute
At the University of South Florida
Objective: To review the role of the radiologist in reporting
tumor measurements in thoracic oncology with emphasis on
newer RECIST criteria and older WHO criteria.
In addition to clinical, biochemical, surgical, and pathologic
data, evaluation of tumor response by quantitative measurements
on cross-sectional imaging provides objective information
regarding chemotherapy efficacy that is used both clinically and
in the development of new anticancer drugs. For these reasons,
radiologists should be familiar with the standards for reporting
tumor measurements that have been established and are widely
used in oncology for clinical trials.
WHO Criteria for Reporting Tumor Response:
The older World Health Organization (WHO) tumor
response assessment criteria were established to standardize the
recording and reporting of tumor response outcomes. 1 This
system utilizes bidimensional measurements as a quantitative
component in the assessment of tumor response to chemotherapy
drugs. Measurements are reported in centimeters (cm) as the
maximum diameter and the greatest perpendicular diameter (at a
right angle) in the same plane for primary and metastatic lesions
whose margins are clearly defined on CT, MRI, or other imaging
study. With this technique, typically up to three lesions per
organ, whose diameters are greater than the image thickness, are
selected as “measurable” and bidimensional measurement values
are then reported. The same acquisition technique must be
utilized for follow-up studies to ensure comparability of subsequent
measurements. Nonmeasurable disease sites are primary
or metastatic lesions which cannot be accurately measured in
two dimensions as they are either measurable in only one
dimension (unidimensional) or are unmeasurable.
In the WHO criteria, the percentage of the decreased or
increased tumor measurements is used to determine whether
there is response or progression of disease, respectively.
Progression of disease (PD) occurs if the surface area approximation
(product of the longest diameter by greatest perpendicular
diameter) for one or more measurable lesions increases by
25% or if one or more new lesions appear. A complete
response (CR) is when all lesions disappear and are absent on
two different observations that are no less than four weeks apart.
A partial response (PR) is noted when the measurable lesions
persist, but have decreased in size by 50% or more as measured
on two different observations not less than four weeks apart.
When measurable disease has not increased more than 25% in
size nor decreased greater than 50% in size, the classification of
“no change (NC)” is given. Both measurable disease and
unmeasurable disease are used in the evaluation of the patient,
with assessment of response involving all parameters. In measurable
disease, the poorest response designation prevails in the
final response classification. 1, 2
RECIST Criteria for Reporting Tumor Response:
In contrast to the standard bidimensional WHO criteria for
the radiologic assessment of response of solid tumors, which
were developed prior to helical CT and other digital imaging
techniques, new guidelines which utilize unidimensional measurements
and modern imaging techniques have been widely
adopted for clinical research protocols. A special report published
in 2000 outlined the new “Response Evaluation Criteria
in Solid Tumors (RECIST). 3 The primary changes with the
newer criteria relate to the adoption of unidimensional tumor
size measurement, better defining the cut-off point for progressive
disease, and specifying clear-cut guidelines about minimum
lesion size and the number of lesions to evaluate when multiple
ones are present.
With the RECIST criteria, only patients with measurable disease
at baseline are included in protocols where objective tumor
response is the primary end point. Measurable disease means
the presence of at least one measurable, histologically confirmed
lesion that can be accurately measured in at least one
dimension of 2 cm or greater for conventional radiographic, CT,
and MRI techniques and 1 cm or greater with helical CT techniques.
Lesions smaller than these values, as well as bone
lesions, leptomeningeal disease, ascites, pleural effusion, pericardial
effusion, lymphangitic carcinomatosis, cystic lesions,
and abdominal masses that are not confirmed and followed by
imaging techniques are considered non-measurable lesions. The
recommendations favor the use of MRI and helical CT given
their reproducibility and ability to consistently display measurable
target lesions. Lesions on chest radiography may be used as
measurable disease if they are clearly defined and surrounded
by aerated lung. Ultrasound (US) should not be used to measure
target lesions for objective tumor response.
With the RECIST criteria, it is important for the radiologist
to properly select and document “target” and “non-target”
lesions. For target lesions, representative measurable lesions up
to a maximum of five per organ and ten in total should be identified
and recorded at baseline. These lesions should be selected
with regard to their size, with longer diameter lesions favored,
as well as lesions which are suitable for accurate, repeated
measurements on imaging follow-up. All other lesions or sites
of disease should be identified as non-target lesions and should
also be recorded at baseline. These lesions are not measured,
but the presence or absence of each should be reported on all
follow-up examinations.
Response criteria with RECIST for target lesions includes
complete response (CR) with the disappearance of all lesions,
partial response (PR) with at least a 30% decrease in the sum
total of the longest diameters of the target lesions compared to
baseline, progressive disease (PD) with the appearance of new
lesions or at least a 20% increase in the sum total of the longest
diameters of the target lesions compared to the smallest sum
total of longest diameters since treatment started, and stable disease
(SD) where there is neither significant tumor shrinkage nor
growth to qualify as PR or PD, respectively. 3
Applications in Thoracic Oncology:
While new protocols will typically utilize the RECIST criteria
to assess solid tumor response to drug therapy, some older
protocols may still be active which used the older WHO criteria.
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