Professor of Radiology, Department of Radiology, Isfahan University of Medical Sciences
CT-Based Response Assessment is main part of our regional practice for lymphoma because in most parts of our country PET/CT is unavailable (as in certain parts of the world). Guidelines are provided for assessing outcome can be categorized as follows: complete response, partial response, stable disease, or progressive disease.
For response evaluation, tumor burden is calculated at baseline by choosing up to six of the largest measurable target lesions (e.g., the largest nodes, nodal mass, or extra nodal deposits in solid organs) representing different body regions and overall disease burden and then performing follow-up evaluations.
Lymph nodes larger than 1.5 cm and extranodal lesions larger than 1.0 cm along their longest diameter are considered to be target lesions, although target nodal lesions are preferable.
The overall objective assessment is performed by measuring the target lesion area as the product of the perpendicular diameters (i.e., the diameter of the long axis multiplied by the diameter of the short axis) and then calculating the sum of the product of the perpendicular diameters of all considered target lesions.
No measurable disease includes lesions too small to be considered measurable, bony skeleton lesions, ascites, pleural and pericardial effusion, spread of lymphangitis, and leptomeningeal disease.
a partial response (PR) was defined as a 50% or greater reduction in the area based on bidimensional measurements.
Likewise, progression in lymphoma is defined as a 50% or greater in the area from nadir.
CR is defined as a complete resolution of all target lesions by CT scans with complete normalization of FDGPET uptake in all areas (Deauville score of 1–3), and bone marrow biopsy negativity (if it was positive or unknown at baseline).
If pretreatment PET scan was negative, lymph nodes that measured 15mm in the long axis should regress to <10 mm. CR is also defined as achievement of a partial remission by CT scan criteria (reduction in sum of longest diameters by CT imaging by >30%) with normalization (Deauville score 1–3) of FDG-PET activity in FDG-avid lymphoma.
There are some differences between RECIST, RECIL, and Lugano assessment which should be considered.