Features of the RECIST 1.1 calculator version 1.0 beta:

Progressive disease is declared when there is an increase in sum of target disease ≥ 20%, stable diease when the change is > -30% and ≤ 20%, partial response when there is a decrease in sum of target disease ≥ 30%, and complete response when all lesions have disappeared or all lesions have disapeared and all nodal disease is < 10 mm each.

If measurements from a previous scan at the nadir represent complete response, progressive disease will be declared if any measurement > 0 mm is entered for a target, unless the check box stating that the lesion is a node is checked, in which case only when the measurement is ≥ 10 mm will progressive disease be declared. i.e. if in a patient with complete response, a lesion that has disappeared, reappears, there is progressive disease.

Progressive disease will not be declared if the sums of target disease do not differ by ≥ 5 mm, unless the difference represents the reappearance of a lesion that had previously disappeared (defined by the user by including a measurement of 0 mm in the nadir column or a normal nodal meaurement (< 10 mm), and a measurement not equal to 0 mm in the current scan column) in a patient who had previous complete response. RECIST 1.1 does not directly specify whether the 5 mm difference applies after complete response in nodal disease. Clearly this is a problem and will be seen if, for example, two nodes are the only targets and they increase from 9 to 10 mm. This will be reported as progressive disease, but you should be careful, this measurement is within the bounds of error and you should use your discretion as well as the allowance in RECIST 1.1 to continue monitoring until a reliable conclusion can be made. This application retains the required 5 mm difference even for nodal disease as it may be inferred that since nodes retain measurement and are almost always present, the same rules as for reappearance of lesions may not apply.

In order to allow modified trial protocols, no prompt will be given to ensure the lesions meet the minimum size criteria for measurable lesions - it is the user's responsibility to select appropriate lesions.

Summary of the Response Evaluation Criteria In Solid Tumours (RECIST) 1.1

A baseline scan is performed not more than one month before the start of treatment. Subsequent response to treatment is evaluated against this scan or the subsequent scan demonstrating the lowest sum of target disease (nadir).

Target lesions are defined at baseline and must be ≥ 10 mm in longest diameter or ≥ 15 mm in short axis if the lesion is a lymph node (although lymph nodes ≥ 10 mm are considered pathological, but non-measurable). If the CT slice thickness is > 5 mm, the extranodal disease must be ≥ twice the slice thickness. Measurable disease on a chest radiograph is ≥ 20 mm, provided the lesion is "clearly defined and surrounded by aerated lung" (1).

A maximum of 5 lesions may be chosen, with a maximum of 2 per organ. The sum of all the extra-nodal long axis measurements and nodal short axis measurements is calculated. When analysing a follow up scan, the same lesions are measured and the sum of target disease is again calculated. Measurements need not be along the same axis (as measured at baseline), but should always be the longest axis of the lesion at that point in time. It does not even have to be at the same slice position, provided the measurement is of the same lesion. However, if the initial measurements are in the axial plane, all further measurements of that lesion must remain in the axial plane. Likewise, if the initial measurements are in the coronal plane (this is acceptable although not well defined in RECIST 1.1), all further measurements of that lesion must be in the coronal plane (assumed).

Bone lesions with a soft tissue component ≥ 10 mm can be designated as target lesions. Sclerotic bone lesions can not be used. Although solid lesions should be used in preference, cystic lesions may be used provided they represent the disease being studied.

If a lesion disappears, the measurement of that lesion is clearly 0 mm, however, if the lesion remains present, but is too small to measure accurately, a default measurement of 5 mm should be given. If lymph nodes decrease to < 10 mm, these are considered to be disease free, but remain target lesions (until new target lesions are selected - usually when disease has progressed and a new baseline scan performed prior to a change in treatment). If lesions merge, the long axis of the resulting lesion is measured as one lesion in place of the individual lesions. If lesions split, the long axis of each individual lesion is added.

An increase of ≥ 20% from the nadir (or baseline, if it represents the point at which the sum of target disease was lowest) represents progressive disease. If the burden of non-target or non-measurable disease increases unequivocally, then progressive disease may be declared, but the increase really must be unequivocal. If a new lesion appears, progressive disease is declared. If, for example, there is doubt as to whether a lesion is new or, say, inflammatory change, follow up scans are required. If the new lesion is confirmed, the date of progression is taken to be the date on which the new lesion was first detected.

A decrease in the sum of target disease of ≥ 30% represents partial response.

Stable disease lies between partial response and progressive disease.

Complete response is the disappearance of all lesions with nodes measuring < 10 mm and normal tumour markers.

If a lesion reappears after disappearing in a patient with complete response, progressive disease is declared. However, if such a lesion behaves in this manner in a patient with stable disease or partial response, it is the change in sum of target disease that defines the response or progression.

PET-CT and MR may be used. The main specification is that imaging protocols are consistent throughout the trial. Therefore, contrast timings, MR sequences and planes should remain the same.

References

1. Eisenhauer EA, Therasse P, Bogaerts J, et al. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur. J. Cancer. 2009;45(2):228–247.

Further reading

2. Van Persijn van Meerten EL, Gelderblom H, Bloem JL. RECIST revised: implications for the radiologist. A review article on the modified RECIST guideline. Eur Radiol. 2010;20(6):1456–1467.
3. Nishino M, Jagannathan JP, Ramaiya NH, Abbeele ADV den. Revised RECIST Guideline Version 1.1: What Oncologists Want to Know and What Radiologists Need to Know. AJR. 2010;195(2):281–289.