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Fig. 3. —Two drawings illustrate method of volumetric analysis for
assessing response of rectosigmoid cancer to radiation therapy. In this
example, for simplicity, lesion is assumed to be cubic shaped, with side
length (L). Right-hand drawing shows size of lesion before radiation therapy
(dotted lines) and after partial response to radiation therapy
(solid lines). Side lengths of cube were reduced by 30%—from 1
L to 0.7 L. This change leads to reduction close to 50% of area of base
(gray) and reduction of 65.7% of volume of cube. According to
Response Evaluation Criteria in Solid Tumors guidelines
[8], partial response to
therapy is present with decrease in lesion maximal diameter of more than 30%.
According to World Health Organization criteria
[6], partial response is
present if decrease of product of maximal perpendicular diameter of lesion is
more than 50%. Relationship between maximal diameter, area, and volume of
lesion has been used to obtain partial response threshold for volumetric
analysis (65.7%).
