Volume doubling time (nodule / tumour growth)

VDT = t × ln 2 ÷ ln(V2 / V1); with diameters V ∝ d³. Solid lung nodule: < 400 days suggests malignant growth (further investigation) · 400–600 days indeterminate · > 600 days slow. Subsolid cancers often double more slowly.

Schwartz M. Cancer 1961;14:1272–94. Callister MEJ et al. BTS guidelines for pulmonary nodules. Thorax 2015;70:ii1–ii54.