Determination of computed tomography number of high-density materials in 12-bit, 12-bit extended and 16-bit depth for dosimetric calculation in treatment planning system

Abstract

AimThe main aim was to examine the effect of bit depth on computed tomography (CT) number for high-density materials. Analysis of the CT number for high-density materials using 16-bit scanners will extend the CT scale that currently exists for 12-bit scanners and thus will be beneficial for use in CT–electron density (ED) curve in radiotherapy treatment planning system (TPS). Implementation of this extended CT scale will compensate for tissue heterogeneity during CT–ED conversion in treatment planning.Materials and methodsAn in-house built phantom with 10 different metal samples was scanned using 80, 100 and 120 kVp in two different CT scanners. A region of interest was set at the centre of the material and the mean CT numbers together with data deviation were determined. Dosimetry calculation was performed by applying a direct anterior beam on 12-bit, 12-bit extended and 16-bit.ResultsHigh-density materials (>4·34 g cm−3) in 16-bit depth provide disparities up to 44% compared to Siemens’ 12-bit extended. Influence of tube voltage showed a significant difference (p<0·05) in both bit depth and CT number of the gold and amalgam saturated in 16-bit depth. A 120 kVp energy illustrated a low variation on CT number for different scanners, but dosimetry calculation showed significant disparities at the metal interface in 12-bit, 12-bit extended and 16-bit.FindingsHigh-density materials require 16-bit scanners to obtain CT number to be implemented in treatment planning in radiotherapy. This also suggests that proper tube voltage together with correct CT–ED resulted in accurate TPS algorithm calculation.

Dosimetric Comparison between Monaco TPS and EGSnrc Monte Carlo simulation on Titanium Rod in 12bit and 16bit Image Format

“…Table 1 shows the CT numbers in different bit depths at 120 kVp, and 12-bit DICOM images saturated at 3071 ± 0 HU for the titanium rod. On the other hand, the mean CT number value is larger in the 12bit extended (8513 ± 31 HU) and 16-bit depth (10006 ± 73 HU) (Jayamani et al, 2019). The 16-bit CT number is 14.9% higher than the 12-bit extended even though both bit-depths are expected to produce similar CT number.…”

Benefits and considerations in using a novel computed tomography system optimized for radiotherapy planning

“…Transitioning to the go.Open Pro provided 16-bit image data, an improvement from the previous 12-bit planning CT (SOMATOM Definition AS Open from Siemens). This increased CT number range enabled a more accurate dose calculation in high-density areas [17] .…”

Impacto Dosimétrico de Curvas CT-to-ED em Irradiações de Heterogeneidades de Alto Número Atômico

“…O número de CT representa a média aritmética de todos os valores de atenuação medidos num volume elementar individual -voxel (4). Estes parâmetros são utilizados para estabelecer uma escala de cinza relativa, atribuindo a cada material, incluindo os de alta densidade, um determinado valor na escala.…”