Lung Nodule Volume Doubling Time Calculator

Volume doubling time (VDT) is the time it takes a nodule to double in volume, assuming exponential growth. It is calculated as VDT = (t × ln 2) / ln(V2 / V1), where t is the interval between scans and V1 and V2 are the earlier and later volumes.

When volume is estimated from diameter by treating the nodule as a sphere (V = π/6 × D³), the volume ratio is the cube of the diameter ratio, so VDT = (t × ln 2) / (3 × ln(D2 / D1)).

Diameter doubling time is 3× VDT.

VDT bands use unrounded values: <400 days, 400–<600 days, and ≥600 days.

Horeweg’s screening analysis advocated VDT assessment for intermediate-size nodules; its size thresholds and participant probabilities are not a complete contemporary management algorithm.

BTS 2015 notes that rapid growth of a new nodule may imply an inflammatory process; rapid growth does not exclude a neoplasm.

In Hong’s selected cohort of resected invasive adenocarcinomas, median VDT for lepidic-predominant tumours was 1140.6 days; 19 of 26 were part-solid on CT. This is not a solid-nodule population reference value.

Each nodule is calculated separately. These calculations do not provide a combined cancer-risk assessment or select an index nodule for management. BTS 2015 recommends basing risk assessment in people with multiple pulmonary nodules on the largest nodule (Grade C).

VDT estimated from one diameter assumes spherical, uniform growth and is less reliable than measured volumetry.

BTS 2015 uses a ≥25% volume change to define significant growth (Grade C); its account of NELSON likewise reports a requirement for at least 25% volume change.

For the evaluated protocols, the criterion that the percentage volume change should be >25% before calculating the VDT was ignored.

These recommendations belong to BTS 2015’s assessment pathway. Initial risk, morphology, reliable measurements, prior imaging and cancer context must be considered; GrowTime does not determine those conditions.

BTS 2015 recommends composite prediction models, based on clinical and radiological factors, to estimate the probability that a nodule ≥8 mm or ≥300 mm³ is malignant (Grade C). GrowTime does not calculate that probability, and its intermediate-size display range (5–<10 mm or 100–<300 mm³ on the first measurement) is a separate convention adapted from Horeweg’s NELSON analysis.

BTS 2015 recommends further diagnostic investigation—biopsy, imaging or resection—for clear growth or VDT <400 days assessed after three months and one year (Grade C).

For nodules in the BTS surveillance pathway with VDT 400–600 days, BTS 2015 offers ongoing yearly surveillance or biopsy according to patient preference (Grade C).

For VDT >600 days, BTS 2015 offers discharge or ongoing CT surveillance, taking account of patient preference, fitness and age (Grade C).

Within its solid-nodule surveillance pathway, BTS 2015 recommends discharge after stability (<25% volume change) on CT after one year (Grade C); a single endpoint comparison does not establish the complete pathway or exclude intervening growth.

When 2D diameter measurements are used to assess growth, BTS 2015 recommends CT follow-up for a total of two years (Grade D).

BTS 2015 recommends no nodule follow-up below 5 mm maximum diameter or 80 mm³ volume (Grade C); this is a separate size-based recommendation, not an inference from a calculated VDT.

In ESTI’s screening pathway, a decrease may indicate a benign process, with ongoing follow-up to ensure shrinkage continues.

Lung-RADS v2022 defines growth as >1.5 mm increase in mean diameter within twelve months; slow-growing solid or part-solid nodules across multiple screening examinations may still be suspicious. GrowTime does not assign Lung-RADS categories.

Fleischner 2017 discusses VDT and the greater reproducibility of volumetry, but its incidental-nodule recommendations are not GrowTime’s three VDT display bands; applicability, morphology, size and prior imaging remain essential.

The 2023 AJR expert-panel review describes volumetry as the primary size method for solid nodules in the European screening position statement and BTS recommendations.

Calculation and contextual guidance reviewed 30 October 2026. BTS 2015 remains the published basis used here; a BTS pulmonary nodules consultation draft is open for comments until 1 December 2026 and is not implemented.

What is the formula for volume doubling time?

VDT = (t × ln 2) / ln(V2 / V1), where t is the time between scans and V1 and V2 are the nodule volumes. If volumes are estimated from diameters assuming a sphere, VDT = (t × ln 2) / (3 × ln(D2 / D1)).

Should I use volume or diameter?

BTS 2015 recommends diameter measurements where volumetry is not possible or there is clear evidence of marked growth (Grade D). BTS 2015 describes NELSON’s failed-volumetry fallback as manually measuring maximum diameter in three perpendicular planes. Horeweg’s thesis manuscript describes estimating unavailable volumes from a manually measured diameter assuming a sphere, while its main diameter measurements were software-derived. These source descriptions differ; GrowTime’s single-diameter spherical estimate does not reproduce BTS’s three-plane account or NELSON’s semiautomated measurements.

What volume doubling time suggests lung cancer?

No calculated VDT diagnoses or excludes cancer. In Horeweg’s NELSON screening analysis, reported 2-year lung cancer probabilities among participants whose largest nodule measured 50–500 mm³ were 9.9% (95% CI 6.9–14.1) for VDT <400 days, 4.0% (1.8–8.3) for VDT 400–<600 days and 0.8% (0.4–1.7) for VDT ≥600 days. These are screening-cohort observations, not this patient’s calculated probability. Growth does not establish malignancy: benign nodules, including hamartomas, can have VDTs comparable to slow-growing cancers. A longer calculated volume doubling time does not establish benignity. Some lung cancers grow slowly.

Can growth be assessed on a 3-month follow-up CT?

BTS 2015 reports better VDT accuracy after one year than after three months, particularly for nodules <6 mm. For screen-detected nodules suitable for volumetry, ESTI’s 2025 recommendation uses substantial-growth thresholds of VDT <250 days at three months, <400 days at six months and <500 days at twelve months or later, accounting for measurement variability. GrowTime does not implement that screening pathway. Diameter change <1.7 mm is within the measurement variability discussed by BTS 2015; the calculated VDT may be unreliable.