Related Experiment Video
Updated: Apr 16, 2026
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
Target delineation variability and corresponding margins of peripheral early stage NSCLC treated with stereotactic
Heike Peulen1, José Belderbos1, Matthias Guckenberger2
1The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Purpose:
To quantify the target delineation variability in peripheral early stage lung cancer treated with SBRT and derive corresponding margins.
Methods And Materials:
Sixteen early stage NSCLC GTV's were delineated by 11 radiation oncologists from 4 institutes. A median surface was computed and the delineation variation perpendicular to this surface was measured (local standard deviation=SD). The overall target delineation variability was quantified by the root-mean-square (rms) of the local SD. The required margin was determined by expanding all delineations to encompass the median surface, where after the underlying probability distribution was modeled by a number of uncorrelated 'pimples-and-dimples'.
Results:
The overall target delineation variability was 2.1mm (rms). Institute I-III delineated significantly smaller volumes than institute IV, yielding target delineation variabilities of 1.2mm and 1.8mm respectively. The margin required to obtain 90% coverage of the delineated contours was 3.4mm and 5.9mm respectively. The factor α in M=αΣ required to calculate adequate margins was 2.8-3.2, which is larger than the 2.5 found for 3D rigid target displacement.
Conclusion:
A relatively small target delineation uncertainty of 1.2mm-1.8mm (1SD) was observed for early stage NSCLC. A 3.4-5.9mm GTV-to-PTV margin was required to account for this uncertainty alone, ignoring other sources of geometric uncertainties.
