Abstract
The study was to describe and to compare the performance of 3D and 4D CBCT imaging modalities by measuring and analyzing the delivered dose and the image quality. The 3D (Chest) and 4D (Symmetry) CBCT Elekta XVI lung IGRT protocols were analyzed. Dose profiles were measured with TLDs inside a dedicated phantom. The dosimetric indicator cone‐beam dose index (CBDI) was evaluated. The image quality analysis was performed by assessing the contrast transfer function (CTF), the noise power spectrum (NPS) and the noise‐equivalent quanta (NEQ). Artifacts were also evaluated by simulating irregular breathing variations. The two imaging modalities showed different dose distributions within the phantom. At the center, the 3D CBCT delivered twice the dose of the 4D CBCT. The CTF was strongly reduced by motion compared to static conditions, resulting in a CTF reduction of 85% for the 3D CBCT and 65% for the 4D CBCT. The amplitude of the NPS was two times higher for the 4D CBCT than for the 3D CBCT. In the presence of motion, the NEQ of the 4D CBCT was 50% higher than the 3D CBCT. In the presence of breathing irregularities, the 4D CBCT protocol was mainly affected by view‐aliasing artifacts, which were typically cone‐beam artifacts, while the 3D CBCT protocol was mainly affected by duplication artifacts. The results showed that the 4D CBCT ensures a reasonable dose and better image quality when moving targets are involved compared to 3D CBCT. Therefore, 4D CBCT is a reliable imaging modality for lung free‐breathing radiation therapy.PACS number(s): 87.57.C‐, 87.57.uq, 87.53.Ly
Highlights
98 Thengumpallil et al.: Difference between lung 3D and 4D image-guided radiotherapy (IGRT) approach is respiratory-correlated cone-beam CT (4D CBCT) tumor motion verification and the correction of the tumor baseline shift based on a registration between the planning 4D CT and 4D CBCT is made prior to delivery, improving the precision of dose delivery.breathing irregularities may substantially reduce the image quality and compromise the dose delivery,(2,4) especially in the case of lung free-breathing radiation therapy (FBRT)
Many respiratory cycles occur during the 4D CBCT acquisition.[2]. The aim of this study was to evaluate the differences between the 3D and 4D CBCT Elekta XVI protocols[6] in terms of dose and image quality, and to investigate their implications on the IGRT accuracy of lung FBRT
Dose profiles and cone-beam dose index (CBDI) The dose within the slices was much more homogeneous for the Chest protocol (Fig. 1(a)) than the Symmetry protocol (Fig. 1(b)). This is due to the fact that the tube rotates only by 200° around the phantom for the Symmetry protocol compared to 360° for the Chest protocol
Summary
98 Thengumpallil et al.: Difference between lung 3D and 4D CBCT tumor motion verification and the correction of the tumor baseline shift based on a registration between the planning 4D CT and 4D CBCT is made prior to delivery, improving the precision of dose delivery.breathing irregularities may substantially reduce the image quality and compromise the dose delivery,(2,4) especially in the case of lung free-breathing radiation therapy (FBRT). Image quality is strongly influenced by image acquisition parameters, such as dose per projection and the number of projections. CBCT are characterized by different image acquisition parameters, affecting dose and image quality in a different manner. This is explained by a slower gantry rotation necessary to ensure adequate angular sampling[5] and more projections are needed to reconstruct more than one CBCT in different breathing phases. Many respiratory cycles occur during the 4D CBCT acquisition.[2] The aim of this study was to evaluate the differences between the 3D and 4D CBCT Elekta XVI protocols[6] in terms of dose and image quality, and to investigate their implications on the IGRT accuracy of lung FBRT
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