  Medical imaging phantoms are widely used for validation and verification of
imaging systems and algorithms in surgical guidance and radiation oncology
procedures. Especially, for the performance evaluation of new algorithms in the
field of medical imaging, manufactured phantoms need to replicate specific
properties of the human body, e.g., tissue morphology and radiological
properties. Additive manufacturing (AM) technology provides an inexpensive
opportunity for accurate anatomical replication with customization
capabilities. In this study, we proposed a simple and cheap protocol to
manufacture realistic tumor phantoms based on the filament 3D printing
technology. Tumor phantoms with both homogenous and heterogenous radiodensity
were fabricated. The radiodensity similarity between the printed tumor models
and real tumor data from CT images of lung cancer patients was evaluated.
Additionally, it was investigated whether a heterogeneity in the 3D printed
tumor phantoms as observed in the tumor patient data had an influence on the
validation of image registration algorithms. A density range between -217 to
226 HUs was achieved for 3D printed phantoms; this range of radiation
attenuation is also observed in the human lung tumor tissue. The resulted HU
range could serve as a lookup-table for researchers and phantom manufactures to
create realistic CT tumor phantoms with the desired range of radiodensities.
The 3D printed tumor phantoms also precisely replicated real lung tumor patient
data regarding morphology and could also include life-like heterogeneity of the
radiodensity inside the tumor models. An influence of the heterogeneity on
accuracy and robustness of the image registration algorithms was not found.
