Cheese-phantom

TomoTherapy Cheese-Phantom (Gammex RMI, Middleton, WI, USA), or equivalent phantoms from other commercial companies, are phantoms for the calibration of CT scanners available at most of the radiotherapy departments. Concretely, the Cheese-Phantom (CP) consists of an 18-cm-thick solid water cylinder with a diameter of 30 cm. The cylinder presents 20 holes with 28 mm of diameter, in which inserts representing the range of densities observed in the clinical environment (tissue inserts) could be placed (Table ​(Table1).1). In our study, for the evaluation of the impact of CT artifacts, three different materials (aluminum, titanium, and steel) were considered. For the simulation of the PET lesions, 6 fillable inserts were developed with a transparent material of density 1.2 g/cm³: 3 large tubes (TL) and 3 small tubes (TS) with volumes 33 and 11 ml, respectively. Metallic, fillable, and tissue inserts were placed in Cheese-Phantom following two configurations: head and neck and prostate carcinoma (Fig. ​(Fig.2).2). The 6 homemade inserts were filled with gallium-68 for the PC configuration and with fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) for the head and neck configuration. The choice for the activity concentrations, volumes, and location of the fillable inserts was based on a previous quantification study of 21 prostate and 16 head and neck PET lesions. In this section, the PET/CT system employed for the 10-min scans was BB, and the segmentation of the 6 fillable spheres on PET images was performed with the 40% algorithm.

Densities of the commercially available (tissue and metallic) placed on the Cheese-Phantom

Setup employed for the identification of radiomic features robust to metal artifacts in PET/CT. Metallic (gray), tissue (brown), and fillable (large tubes (TL) and small tubes (TS), blue) inserts were placed in Cheese-Phantom following the head and neck and prostate carcinoma configurations