ESTRO meets Asia 2024 - Abstract Book

S231

Interdisciplinary – Other

ESTRO meets Asia 2024

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Digital Poster

DOSEMETRIC VALIDATION OF THE DIRECTDENSITY RECONSTRUCTION ALGORITHM

CARMEN GIL LOPEZ

Radiofisica, Hospital Son Espases, Palma de Mallorca, Spain

Purpose/Objective:

The calibration curves between Hounsfield Units (HU) and relative electron density or mass density to water of external radiotherapy planning systems are dependent on acquisition parameters and CT image reconstruction algorithm, with tube voltage being the parameter that most influences HU. The Siemens DirectDensity reconstruction algorithm obtains this linear and voltage-independent relationship, allowing the user to optimize image quality for different acquisition protocols without affecting dose calculation. When calculating the dose, we must select from different calculation algorithms that use different calibration curves. DirectDensity uses a single calibration curve for all voltages and provides 3 types of reconstructions. This study dosimetrically evaluates the calibration curves of CT generated by DirectDensity reconstruction algorithms.

Material/Methods:

We will use the 'Tissue Characterization Phantom Model 467-Gammex' phantom, a Siemens Healthineers CT scanner, and the Eclipse® version 13.6 treatment planning system from Varian Inc.

Figure 1. Phantom

The Hounsfield Units (HU) of the abdomen and head protocols were measured on the CT scanner, and the mean was calculated for the two reconstructions (electron density (eDD) and mass density (mDD)). Knowing the actual electron densities of each insert, a least squares adjustment was made to calculate the estimated electron