Initial evaluation of a four‐dimensional computed tomography system, using a programmable motor

Abstract

A dynamic lung tumor phantom was used to investigate the geometric reconstruction accuracy of a commercial four‐dimensional computed tomography (4D‐CT) system. A ball filled with resin, embedded in a cork cube, was placed on a moving platform. Various realistic antero‐posterior (AP) motions were programmed to reproduce the respiratory motion of a lung tumor. Several three‐dimensional (3D) CT and 4D‐CT images of this moving object were acquired and compared using different acquisition parameters. Apparent volume and diameter of the ball were measured and compared to the real values. The position of two points (the AP limits of the ball) during the motion in the coordinate system of the CT scanner were also compared with the expected values. Volume error was shown to increase with object speed. However, although the volume error was associated with intraslice artifacts, it did not reflect large interslice inconstancies in object position and should not be used as an indicator of image accuracy. The 3D‐CT gave a random position of the tumor along the phantom excursion; accuracy in the assessment of position by 4D‐CT ranged from 0.4 mm to 2.6 mm during extreme phases of breathing. We used average projection (AVE) and maximum intensity projection (MIP) algorithms available on the commercial software to create internal target volumes (ITVs) by merging gross tumor volume (GTV) images at various respiratory phases. The ITVs were compared to a theoretical value computed from the programmed ball excursion. The ITVs created from the MIP algorithm were closer to the theoretical value (within 12%) than were those created from the AVE algorithm (within 40%).PACS numbers: 87.53.Xd, 87.56.Mp, 87.57.Ce, 87.59.Fm

Do Maximum Intensity Projection Images Truly Capture Tumor Motion?

“…Using dynamic magnetic resonance imaging for real patients, MIP-based internal target areas were shown to be comparatively smaller than internal target areas generated by means of magnetic resonance imaging (11). Using a phantom moving along the anterior-posterior direction, ITVs created from the MIP were found to be closer to the theoretical value than those created from the AVG (13). In this study, we investigated the correlation of MIP images with breathing irregularity and such scan parameters as gantry speed by taking advantage of the accuracy and reproducibility of a programmable lung phantom.…”

Optimizing geometric accuracy of four-dimensional CT scans acquired using the wall- and couch-mounted Varian® Real-time Position Management™ camera systems

“…A number of authors suggested that a faster rotation speed should result in reduced artefact, [8][9][10] although this had not been investigated using maximum velocity with the same detail as presented by Nakamura et al 8 for a 1-s rotation time. The presented work further shows that using a faster tube rotation speed results in less delineation errors for outlining mid-phase targets with the least error shown at maximum inhalation and maximum exhalation, consistent with previous observations.…”

“…The presented work further shows that using a faster tube rotation speed results in less delineation errors for outlining mid-phase targets with the least error shown at maximum inhalation and maximum exhalation, consistent with previous observations. 9 This is particularly true for high amplitude movement combined with fast-breathing periods.…”

“…[8][9][10]12,14 This study presented length changes to allow better estimations of the margins expected if all phases are used for target definition in building an ITV or for treatment using 4D-VMAT. 6 Indeed, it has recently been shown that the MIP may not be adequate in defining the target for the oesophagus, 15 and therefore an increasing amount of information is required for target definition across all phases.…”

“…9 The image noise increases when using a faster tube rotation speed while maintaining the same mA because images are acquired in less time and therefore constructed from a reduced number of X-ray photons. Thus, in our study we aim to determine if a higher tube current is necessary to compensate for the resulting loss in signal-to-noise ratio.…”