Volume doubling time (VDT) calculator for pulmonary nodules (volume-based)

Note to first time users: This calculator requires the volume of the investigated nodule at the initial and follow-up examinations. This should be obtained whenever possible via volumetry. Alternatively you can obtain an approximate nodule volume with a spherical formula here, however be aware that this only gives a rough estimate of the VDT. As a further alternative (e.g. for subsolid nodules) you can use this diameter-based formula, however note that this method is also less reliable. The calculator can also be used to check whether based on the initial nodule volume follow-up and VDT calculation are a reasonable approach to management. Please read the detailed ‘Notes’ section below too.

Notes

Formula

• This calculator uses the modified Schwartz formula:
  • VDT = [ ln₂ × ∆T ] / [ ln( X₂ / X₁ ) ]
    • X₂ and X₁ = the final and initial nodule volumes
    • ∆T = time (in days) between the two scans
    • ln = natural logarithm

How to interpret the VDT

• The NELSON, UK Lung Cancer Screening Trial, and the Danish Lung Cancer Screening Trial studies used VDTs <400 days as the trigger for further investigation in indeterminate lung nodules.
• It must be stressed that these studies only considered a VDT <400 days clinically important if it was accompanied by >25% nodule volume growth.
• Important caveats apply to large lesions where tumor volume exceeding the vascular supply can result in a misleadingly long VDT. Also it must be stressed that some smaller malignant lesions can demonstrate long periods of slow growth followed by rapid increase over a short period of time. In all cases VDT is only one of the several features one has to consider while assessing lung nodules.
  • ^{Devaraj A, van Ginneken B, Nair A, Baldwin D. Use of Volumetry for Lung Nodule Management: Theory and Practice. Radiology. 2017 Sep;284(3):630-644. doi: 10.1148/radiol.2017151022. PMID: 28825886.}
• The NELSON trial has demonstrated the following:
  • Patients with <100 mm³ (or <5 mm diameter) nodules have a low lung cancer risk (0.4-0.6%).
  • Cancer risk is intermediate for 100-300 mm³ (5-10 mm diameter) nodules (1.3-2.4%). For these lesions follow-up imaging with VDT calculation can be particularly useful.
  • >300 mm³ (and/or >10 mm diameter) nodules have a high risk of malignancy. Immediate further diagnostic workup (e.g. PET-CT) is warranted rather than follow-up and VDT calculation!
• VDT-based lung cancer risk was as follows:
  • VDT >600 days: 0.8%
  • 400-600 days: 4%
  • <400 days: 9.9%
  • ^{Horeweg N, van Rosmalen J, Heuvelmans MA, van der Aalst CM, Vliegenthart R, Scholten ET, ten Haaf K, Nackaerts K, Lammers JW, Weenink C, Groen HJ, van Ooijen P, de Jong PA, de Bock GH, Mali W, de Koning HJ, Oudkerk M. Lung cancer probability in patients with CT-detected pulmonary nodules: a prespecified analysis of data from the NELSON trial of low-dose CT screening. Lancet Oncol. 2014 Nov;15(12):1332-41. doi: 10.1016/S1470-2045(14)70389-4. Epub 2014 Oct 1. PMID: 25282285.}

Acquisition parameters are important too

• Especially for small nodules using similar acquisition parameters for the initial and follow-up CT examinations is crucial.
• Comparisons between e.g. a noncontrast and contrast enhanced CT are less reliable and should be treated with caution.
• Factors such as slice thickness, pitch, and reconstruction kernel technique (filtered backprojection vs. iterative) can also potentially influence volumetric measurements.
  • ^{Mohamed Hoesein FA, Bülbül M, de Jong PA. Pulmonary nodule follow-up: be careful with volumetry between contrast enhanced and unenhanced CT. Ann Transl Med. 2016 Sep;4(18):346. doi: 10.21037/atm.2016.08.43. PMID: 27761450; PMCID: PMC5066033.}

Last updated: 2021-08-25