Assessing margin expansions of internal target volumes in 3D and 4D PET: a phantom study

• Published in: Annals of nuclear medicine Vol. 29; no. 1; pp. 100 - 109
• Main Authors: Jani, Shyam S., Lamb, James M., White, Benjamin M., Dahlbom, Magnus, Robinson, Clifford G., Low, Daniel A.
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Japan 01-01-2015; Springer Nature B.V
• Subjects: Algorithms; Humans; Imaging; Imaging, Three-Dimensional - instrumentation; Imaging, Three-Dimensional - methods; Lung - diagnostic imaging; Lung - physiopathology; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - physiopathology; Medicine; Medicine & Public Health; Models, Biological; Normal Distribution; Nuclear Medicine; Original Article; Phantoms, Imaging; Positron-Emission Tomography - instrumentation; Positron-Emission Tomography - methods; Radiology; Respiration; Robotics; Tumor Burden; 4D-PET; Lung cancer
• ISSN: 0914-7187; 1864-6433
• DOI: 10.1007/s12149-014-0914-x

Background and Purpose
To quantify tumor volume coverage and excess normal tissue coverage using margin expansions of mobile target internal target volumes (ITVs) in the lung.
Materials and methods
FDG-PET list-mode data were acquired for four spheres ranging from 1 to 4 cm as they underwent 1D motion based on four patient breathing trajectories. Both ungated PET images and PET maximum intensity projections (PET-MIPs) were examined. Amplitude-based gating was performed on sequential list-mode files of varying signal-to-background ratios to generate PET-MIPs. ITVs were first post-processed using either a Gaussian filter or a custom two-step module, and then segmented by applying a gradient-based watershed algorithm. Uniform and non-uniform 1 mm margins were added to segmented ITVs until complete target coverage was achieved.
Results
PET-MIPs required smaller uniform margins (4.7 vs. 11.3 mm) than ungated PET, with correspondingly smaller over-coverage volumes (OCVs). Non-uniform margins consistently resulted in smaller OCVs when compared to uniform margins. PET-MIPs and ungated PET had comparable OCVs with non-uniform margins, but PET-MIPs required smaller longitudinal margins (4.7 vs. 8.5 mm). Non-uniform margins were independent of sphere size.
Conclusions
Gated PET-MIP images and non-uniform margins result in more accurate ITV delineation while reducing normal tissue coverage.