ESTRO 2024 - Abstract Book

S3820

Physics - Image acquisition and processing

ESTRO 2024

The Model 062M Electron density phantom (CIRS) has been scanned both with a titanium insert of known density and thickness and without it. For each CT scan, two reconstructions were performed, one using the Standard reconstruction (Br40) and the other using Direct Density reconstruction (Sd36), resulting in a total of four CT datasets. For the two CT scans without the metal insert (Standard and Direct Density), the density has been overwritten to the theoretical density of the metal insert at the location where it should be placed. For all CT datasets, a PTV (28.53 cc) has been delineated in the vicinity of the metal, and a VMAT plan with a prescription of 10 Gy (AAA v.16, Eclipse) using two arcs has been created, avoiding the entry of the beam into the metal. The same plan has been carried out in all the CT scans. Besides assessing the PTV, the dosimetry has been evaluated in a control region (32.21 cc) around the metal, and through a gamma analysis (2% 2 mm) [2]. Additionally, a patient with a metal prosthesis has been planned using Direct Density and Standard CT reconstructions. These dosimetry have been evaluated by comparing results in PTV, OARs, and gamma analysis (2% 2 mm).

Results:

The dose results for the four CT scans of the Model 062M Electron density phantom are shown in Table 1 and gamma results are shown in Table 2.

Table 1. Where EDD Tit refers to the electron Direct Density reconstruction with Titanium, Stand Tit refers to the Standard reconstruction with Titanium, EDD Ftit refers to the electron Direct Density reconstruction without titanium, and Stand Ftit refers to the Standard reconstruction without titanium. In Ftit reconstructions the density has been overwritten to titanium density in the respective locations.

Gamma (%)

EDD Ftit/Stand Ftit

100.00

EDD Ftit/EDD Tit

99.70

Stand Tit/ Stand FTit

99.49

EDD Tit/Stand Ftit

99.74

Stand Tit/ EDD Ftit

99.43

Table 2. Gamma results (2% 2 mm) between the dosimetry of different reconstructions.

Table 3. Dose comparison for the plan calculated with both CT reconstructions for a patient with a pelvic prosthesis.