About this Small Lung Nodule Profile

The purpose of a profile document is to serve as an implementation guide for an imaging biomarker to achieve a claimed level of technical performance in a defined clinical setting. For the Small Lung Nodule Profile, the clinical setting is chest-CT lung cancer screening. This profile has been developed by the Small Lung Nodule Biomarker Committee to improve the reliability, consistency, and clinical utility of quantitative CT volumetry for small solid lung nodules detected in low-dose CT screening. By specifying methods and performance expectations, this document provides guidance to help ensure that changes in nodule volume can be interpreted confidently and to distinguish true biological growth from measurement variation.

In lung cancer screening, many nodules detected are small, often between 6 and 10 mm in diameter, where visual assessment alone is unreliable, and this size range is the focus of the current quantitative performance claims in this guidance. Even small inconsistencies in image acquisition, reconstruction, or analysis can produce apparent changes in nodule size that may not represent real growth. This guidance provides a framework to minimize those inconsistencies across equipment, institutions, and time.

Essence:

When comparing CT volumes of a pulmonary nodule between two screening rounds, the measurement is only as dependable as its technical uncertainty. For example, two scans might suggest a 25% increase in nodule volume; however, if the measurement variability is of the same magnitude, it is impossible to conclude whether the nodule truly grew or the difference is due to imaging noise or reconstruction settings.

This Guidance provides information regarding the expected within-subject coefficient of variation (wCV) and corresponding confidence intervals for volumetric CT measurements of small solid nodules (“Claims”). These performance claims are derived from the approach developed by the Quantitative Imaging Biomarkers Alliance, which was started by the Radiological Society of North America in 2007 to advance quantitative imaging. The sponsorship of this Biomarker Committee transitioned from QIBA to American Lung Association in 2024 to continue to allow the guidance to evolve from lung cancer screening to integrated chest CT screening for other co-morbid conditions of the chest. However, the Small Lung Nodule Biomarker Committee continues to work with the successor organization for QIBA, called the Quantitative Medical Imaging Coalition (QMIC), which supports quantitative imaging and hosts many of the legacy versions of the QIBA Profiles.   

The guidance describes:

  • How each actor (radiologist, radiographer, medical physicist, and image analyst) contributes to achieving reliable measurements.

  • The technical factors that must be controlled (scanner calibration, acquisition protocol, reconstruction parameters, and image analysis).

  • A Conformance Checklist to evaluate whether a site or scanner meets the defined performance criteria.

This information supports clinicians in interpreting small changes in nodule volume and researchers in designing trials with appropriate statistical power.

Understanding Limitations:

This guidance supports consistent quantitative measurements but does not prescribe standards of care or replace clinical judgment. Individual patient factors, such as breath-hold quality, comorbidities, or artifacts from medical devices, can still limit measurement accuracy. 

Furthermore, the parameters described are specific to solid nodules; part-solid or ground-glass nodules behave differently and are outside the scope of this version. The guidance focuses on reducing technical variability, not on establishing diagnostic thresholds or management decisions, which remain the responsibility of clinical teams.

In Practice:

This guidance and its accompanying Conformance Checklist serve as a practical tool for both clinical and research implementation. It can be integrated into site qualification for lung cancer screening programs, equipment acceptance and maintenance procedures, and training materials for radiology staff and quality assurance teams. 

The ultimate goal is to ensure that a measured change in nodule volume truly reflects a biological change in the nodule itself, thereby strengthening the reliability and confidence of applying quantitative CT screening programs across diverse healthcare settings.