recist 1.1 calculator

What this RECIST 1.1 calculator does

This tool gives a quick, structured interpretation of treatment response for target lesions using RECIST 1.1 logic. It is designed for clinical education and workflow support, not for replacing radiology reports or oncologist judgment.

It calculates percentage change from baseline and from nadir, then applies the common decision sequence used in oncology follow-up: complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD).

RECIST 1.1 response rules used in the calculator

Target lesion criteria

• CR (Complete Response): disappearance of all target lesions and pathologic nodes reduced to < 10 mm short axis.
• PR (Partial Response): at least a 30% decrease in sum of target lesion diameters, using baseline as the reference.
• PD (Progressive Disease): at least a 20% increase from nadir, and at least 5 mm absolute increase.
• SD (Stable Disease): neither PR nor PD criteria are met.

Automatic progression overrides

• Any new lesion is considered PD.
• Unequivocal progression of non-target lesions is considered PD.

How to use it correctly

1) Enter measurements in mm

Use the sum of diameters of target lesions from your baseline and current scan. Keep measurement technique consistent across timepoints whenever possible.

2) Add nadir for progression checks

Nadir means the smallest prior sum observed on study. If left blank, this calculator defaults nadir to baseline for convenience.

3) Check clinical/radiologic override boxes

If there are new lesions or unequivocal non-target progression, RECIST classification moves to PD regardless of target lesion shrinkage.

Worked example

Suppose baseline sum is 100 mm, nadir is 60 mm, and current sum is 74 mm:

• Change from baseline: -26% (not enough for PR)
• Change from nadir: +23.3%
• Absolute increase from nadir: +14 mm

Because increase from nadir is at least 20% and absolute increase is at least 5 mm, the category is PD.

Practical tips for RECIST consistency

• Use the same lesion targets across visits unless formally updated.
• Document which lesions are nodal vs non-nodal; nodal criteria differ in RECIST 1.1.
• Confirm whether nadir includes all prior visits and matches your trial/site convention.
• Record unit consistency (mm) and avoid mixing long-axis and short-axis rules incorrectly.

Important limitation and medical disclaimer

This calculator is a simplified decision aid and does not capture the full complexity of oncology response assessment, protocol-specific rules, iRECIST modifications, or patient-specific context. Final interpretation must come from qualified clinical professionals using complete imaging and clinical data.