RECIST 1.1 Calculator for Tumor Response

This calculator helps assess solid tumor response to treatment according to RECIST 1.1 criteria by calculating the percentage change in the sum of longest diameters of target lesions.

What is a RECIST Calculator?

A RECIST (Response Evaluation Criteria in Solid Tumors) calculator is a tool used by oncologists and radiologists to standardize the assessment of how solid tumors respond to cancer treatment. The most current version is RECIST 1.1. It provides objective criteria to determine whether a tumor disappears, shrinks, stays the same, or gets bigger.

RECIST 1.1 Formula and Explanation

The core of RECIST 1.1 is the percentage change in the sum of the longest diameters (SLD) of target lesions.

Formula:

% Change = ((Follow-up SLD - Baseline SLD) / Baseline SLD) * 100

RECIST 1.1 Response Categories

Response Category	Criteria
Complete Response (CR)	Disappearance of all target lesions.
Partial Response (PR)	At least a 30% decrease in the SLD of target lesions, taking as reference the baseline SLD.
Progressive Disease (PD)	At least a 20% increase in the SLD of target lesions, taking as reference the smallest SLD recorded since the treatment started or the appearance of one or more new lesions.
Stable Disease (SD)	Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD.

Practical Examples

Example 1: Partial Response

• Baseline SLD: 100 mm
• Follow-up SLD: 60 mm
• Calculation: ((60 – 100) / 100) * 100 = -40%
• Result: Partial Response (PR), as the decrease is more than 30%.

Example 2: Progressive Disease

• Baseline SLD: 80 mm
• Follow-up SLD: 100 mm
• Calculation: ((100 – 80) / 80) * 100 = +25%
• Result: Progressive Disease (PD), as the increase is more than 20%.

How to Use This RECIST Calculator

1. Enter the sum of the longest diameters of the target lesions from the initial (baseline) scan into the “Baseline Sum” field.
2. Enter the sum of the longest diameters from the subsequent (follow-up) scan into the “Follow-up Sum” field.
3. Click “Calculate Response” to see the percentage change and the RECIST 1.1 response category.
4. Use the “Reset” button to clear the fields or “Copy Results” to copy the outcome.

Key Factors That Affect RECIST Assessment

• Image Acquisition Quality: Consistent imaging protocols are crucial for accurate measurements.
• Lesion Selection: Proper identification of target lesions is fundamental.
• Measurement Technique: The method used to measure the longest diameter can introduce variability.
• Presence of New Lesions: The appearance of any new lesion automatically signifies progressive disease.
• Non-Target Lesions: Changes in non-target lesions can also affect the overall assessment.
• Inter-observer Variability: Different radiologists might measure lesions slightly differently.

Frequently Asked Questions

What does RECIST stand for?

Response Evaluation Criteria in Solid Tumors.

What is a target lesion?

A measurable lesion, typically at least 10 mm in its longest diameter, chosen for repeated assessment.

What is the maximum number of target lesions in RECIST 1.1?

A maximum of five target lesions in total, and no more than two lesions per organ.

What constitutes a “new lesion”?

Any lesion identified on a follow-up scan that was not present at baseline. The appearance of a new lesion is considered progressive disease.

How are lymph nodes measured?

Lymph nodes are measured in their short axis. A node must be at least 15 mm in the short axis to be a target lesion.

What if a target lesion disappears?

If all target lesions disappear, it is considered a Complete Response (CR).

Does this calculator work for all cancer types?

RECIST is primarily for solid tumors. Other criteria exist for specific cancers like lymphoma or GIST.

Where can I find the official RECIST guidelines?

The RECIST working group provides documentation and resources on their official website.