The effect of irregular breathing patterns on internal target volumes in four-dimensional CT and cone-beam CT images in the context of stereotactic lung radiotherapy

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

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis

Thengumpallil

Smith

Monnin

et al. 2016

“…The ITV‐PTV margins for anterior‐posterior, superior‐inferior, and left‐right directions in our study theoretically should be 7.9 mm, 6.2 mm, and 5.0 mm, which indicates that an isotropic margin of 5.0 mm might not be sufficient. A phantom study (18) has been performed on the effect of irregular breathing patterns on the ITVs and superior‐inferior lengths delineated on CBCT and 4D CT MIP. According to their results, ITVs delineated on 4D CT MIP and CBCT were reduced by up to 20% and 30% and shortened by up to 7 and 11 mm when irregular motion was introduced.…”

Section: Discussionmentioning

confidence: 99%

“…Though several setup methods, including soft‐tissue‐based setup and bony‐structure‐based setup, were adopted in clinical practice, bony‐structure‐based registration is the basic assumption for the evaluation of interfractional variation of ITV centroid position. Because the pattern and amplitude of breathing will vary from fraction to fraction and it will have an impact on the imaging results of CBCT, (18) there are still many uncertainties when registering CBCT with 4D CT using soft‐tissue‐based setup method and it will help determining ITV‐PTV margin in case no soft‐tissue‐based setup is available during SBRT treatment. However, bony structure is relatively stable and identifiable in CBCT images.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of interfractional variation of the centroid position and volume of internal target volume during stereotactic body radiotherapy of lung cancer using cone‐beam computed tomography

Sun

Cheng

et al. 2016

The purpose of this study was to determine interfractional variation of the centroid position and volume of internal target volume (ITV) during stereotactic body radiation therapy (SBRT) of lung cancer. From January 2014 to August 2014, a total of 32 patients with 37 primary or metastatic lung tumors were enrolled in our study. All patients received SBRT treatment in 4–5 fractions to a median dose of 48 Gy. Both 3D CT and 4D CT scans were used for radiotherapy treatment planning. 3D CBCT was acquired prior to treatment delivery to verify patient positioning. A total of 163 3D CBCT images were available for evaluation. 3D CBCT scans acquired for verification were registered with simulation CT scans. The ITVs were contoured on all verification 3D CBCT scans and compared to the initial gross target volume (GTV) or ITV in treatment planning system. GTV was based on 3D CT while ITV was based on both 3D CT and 4D CT. To assess the interfractional variation of ITV centroid position, we used vertebrae body adjacent to the tumor as reference point when performing the registration procedure. To eliminate the effect of time on tumor volume between simulation CT scan and the first fraction, the interfractional variation of ITV was evaluated from the first fraction to the last fraction. The overall 3D vector shift was 4.4±2.5 mm (range: 0.4−13.8 mm). The interfractional variation of ITV centroid position in superior‐inferior, anterior‐posterior, and left‐right directions were −0.7±2.7 mm, −1.4±3.4 mm, and −0.5±2.2 mm, respectively. No significant difference was observed between three directions (p=0.147). Large interfractional variations (≥5 mm) were observed in 12 fractions (9.3%) in superior‐inferior direction, 24 fractions (18.6%) in anterior‐posterior direction, and 5 fractions (3.9%) in left‐right direction. No time trend of tumor volume change measured in 3D CBCT was detected during four fractions (p=0.074). A significant (p=0.010) time trend was detected when evaluating the time trend of ITV change during 5 fractions and diameter was found to be significantly correlated with the ITV change (p=0.000). ITV did not show significant regression during SBRT treatment, but interfractional variation in the ITV centroid position was observed, especially in anterior‐posterior direction. An isotropic margin of 7 mm around ITV might be necessary for adequate coverage of interfractional variation of ITV centroid position, but only in case no soft tissue‐based setup is performed during SBRT treatment.PACS number(s): 87.55.dk

“…Conversely, the use of maximum intensity projection (MIP) images can induce inaccuracies in motion assessment, particularly for irregular breathing patterns 10, 11. Organs in every other breathing phase were assessed to ensure that the union structure fully encompassed each organ's extreme positions in all breathing phases.…”

Section: Methodsmentioning

confidence: 99%

Organ motion in pediatric high‐risk neuroblastoma patients using four‐dimensional computed tomography

Kannan

Teo

Solberg

et al. 2016

Purpose/objective(s)High‐risk neuroblastoma (HR‐NBL) requires multimodality treatment, including external beam radiation of the primary tumor site following resection. Radiotherapy planning must take into account motion of the target and adjacent normal anatomy, both of which are poorly understood in the pediatric population, and which may differ significantly from those in adults.Methods/materialsWe examined 4DCT scans of 15 consecutive pediatric patients treated for HR‐NBL, most with tumors in the abdominal cavity. The diaphragm and organs at risk were contoured at full inhale, full exhale, and on free‐breathing scans. Maximum displacement of organs between full inhale and full exhale was measured in the anterior, posterior, superior, inferior, left, and right directions, as was displacement of centroids in the A/P, S/I, and L/R axes. Contours on free‐breathing scans were compared to those on 4D scans.ResultsMaximum displacement was along the S/I axis, with the superior aspects of organs moving more than the inferior, implying organ compression with respiration. Liver and spleen exhibited the largest motion, which correlated strongly with the S/I motion of the diaphragm. The maximum organ motion observed in the abdomen and thorax were 4.5 mm and 7.4 mm, respectively, while maximum diaphragm displacement was 5.7 mm. Overall findings mirrored observations in adults, but with smaller magnitudes, as expected. No consistent margins could be added to the free‐breathing scans to encompass the motion determined using 4DCT.ConclusionsOrgan motion within the pediatric abdomen and pelvis is similar to that observed in adults, but with smaller magnitude. Precise margins to accommodate motion are patient‐specific, underscoring the need for 4DCT scanning when possible.