Brock below 10%
CT surveillance is generally used, with timing shaped by size or volume, morphology, and growth.
Full PanCan / McWilliams model
Brock Pulmonary Nodule Risk Calculator
Estimate pulmonary nodule malignancy probability with the published full nine-predictor Brock model, then place the result in the British Thoracic Society diagnostic pathway.
Full model coefficientsBTS threshold contextEvidence reviewed August 2026
Educational clinical decision support. The result is a population-model estimate, not a cancer diagnosis or patient-specific order. Confirm CT features, prior imaging, growth, model applicability, and local multidisciplinary practice.
Full PanCan model
Enter the published Brock predictors
Use CT descriptors from the radiology report whenever possible. The model uses maximum diameter—not the average diameter used by Fleischner tables.
Patient-level predictors
The published model encodes sex as a binary variable. This is a limitation of the derivation data, not a statement about identity.
Nodule and CT predictors
Calculated locally in your browserNo patient data uploadedPublished model version displayed
BTS diagnostic pathway
What the 10% Brock threshold means
The published BTS guideline recommends the full Brock model for initial malignancy estimation in appropriate nodules. A result above 10% moves to PET-CT when the nodule is large enough for local PET detection, followed by Herder-model reassessment. It does not mean a 10% result should automatically be biopsied.
Brock above 10%
Offer PET-CT when technically appropriate, then recalculate probability with the Herder model.
After PET-CT
Management decisions use the post-PET estimate, patient fitness, preferences, and multidisciplinary review.
Different questions
Brock versus Fleischner
Brock estimates cancer probability. The Fleischner nodule assistant summarizes surveillance intervals for eligible incidental nodules. Keep the measurement convention straight: Brock uses maximum diameter; Fleischner uses an averaged diameter.
Upstream context
Screening eligibility is separate
The Brock result does not determine whether someone should receive annual LDCT screening. Use the pack-year and LDCT eligibility calculator for current screening criteria and exposure history.
Transparent calculation
How the full Brock model is calculated
The full model keeps the nonlinear diameter transformation, spiculation, and every published coefficient. The calculation happens in two steps.
1
Build the linear predictor
Calculate LP
Baseline− 6.7892
Age+ 0.0287 × (age − 62)
Patient+ 0.6011 × female + 0.2961 × family history + 0.2953 × emphysema
Diameter− 5.3854 × [(diameter ÷ 10)⁻⁰·⁵ − 1.58113883]
Nodule+ attenuation + 0.6581 × upper lobe
CT context− 0.0824 × (nodule count − 4) + 0.7729 × spiculation
2
Convert LP to probability
Apply the logistic function
P = 100 ×eLP1 + eLP
The result is multiplied by 100 and displayed as the estimated malignancy probability.
Coefficient key
How categorical inputs are encoded
For yes/no predictors: yes = 1 and no = 0
Solid nodule
0
Reference category
Part-solid nodule
+0.3770
Added to LP
Pure ground-glass
−0.1276
Added to LP
Model inputs: age, model-encoded sex, first-degree family history of lung cancer, emphysema, maximum nodule diameter, attenuation, upper-lobe location, total nodule count, and spiculation.
Model boundaries
Where the estimate needs extra caution
Screening-derived population
The model came from screening cohorts enriched for smoking exposure. Calibration may differ in incidental, never-smoking, regional, and referral populations.
Imaging inputs matter
Spiculation, attenuation, count, and maximum diameter should come from a high-quality CT interpretation. Entry error directly changes the estimate.
Subgroup performance varies
A 2025 meta-analysis found variation by nodule size, attenuation, population, and solitary versus multiple nodules despite good overall discrimination.
Not for every lung lesion
Do not use this 1–30 mm nodule tool for a pulmonary mass, obvious benign calcification, acute infectious process, or as a substitute for growth assessment.
Binary sex encoding
The original coefficient set only provides male and female categories. This limits applicability outside the derivation variable structure.
Probability is not management
Symptoms, prior cancer, patient fitness, preferences, PET availability, and multidisciplinary judgment can change the pathway.
Frequently asked questions
Brock score and pulmonary nodule cancer risk
What is a Brock score for a lung nodule?
The Brock score is a calculated probability that a CT-detected pulmonary nodule is malignant. It combines patient-level and CT-level predictors from the full PanCan model; it is an estimate, not a diagnosis.
What Brock score leads to PET-CT?
The published BTS pathway uses a Brock probability above 10% to offer PET-CT when the nodule is above the local PET detection threshold. PET findings then enter the Herder model; 10% is not an automatic biopsy threshold.
Is Brock the same as Fleischner?
No. Brock estimates malignancy probability. Fleischner recommendations provide follow-up intervals for eligible incidentally detected nodules. A clinician may use both within a broader pathway, but one does not replace the other.
Which nodule size should I enter?
Enter the maximum nodule diameter in millimeters for the modeled nodule. This differs from the average of long- and short-axis diameters used in Fleischner size categories. Use consistent thin-section CT measurements and the radiology report.
Why does Brock ask for the number of nodules?
Nodule count is an independent term in the published model. Holding all other predictors constant, a lower total nodule count increases the calculated probability for the modeled nodule.
Does the Brock model use smoking history?
Smoking exposure is not an input in the published full model used here. The model was developed in screening cohorts enriched for current and former smokers, so clinicians should consider transportability and local calibration in other populations.
Can Brock be used for ground-glass and part-solid nodules?
The full model includes solid, part-solid, and non-solid attenuation. Performance and calibration may differ across nodule subgroups, so morphology, persistence, growth, and guideline context remain essential.
Should I use Brock for a lesion larger than 30 mm?
No. A lesion larger than 30 mm is a pulmonary mass rather than a nodule and falls outside this calculator. It requires an individualized diagnostic pathway.
Evidence base
Primary study, guideline, and validation material
Evidence and source availability reviewed August 16, 2026. The BTS pulmonary nodule guideline was published in 2015; its update group is active, so the publication year and current review status are stated separately.
McWilliams et al. Probability of Cancer in Pulmonary Nodules Detected on First Screening CT (NEJM, 2013)Primary PanCan model derivation and external validation study.British Thoracic Society Guidelines for the Investigation and Management of Pulmonary Nodules (Thorax, 2015)Published BTS pathway recommending full Brock-model estimation and the 10% PET-CT threshold.BTS Pulmonary Nodule Risk CalculatorOfficial BTS implementation and explanation of the Brock and Herder models.Tammemägi et al. Evaluation of Prediction Models for Pulmonary Nodules (JAMA Network Open, 2020)External evaluation and recalibration of lung-nodule malignancy models in screening data.Wang et al. Diagnostic accuracy of the Brock model: systematic review and meta-analysis (2025)Contemporary pooled evaluation showing better performance for the full model and variation by population and nodule characteristics.
BTS Pulmonary Nodules Guideline Update Group PulmTools pulmonology cluster
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