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Title: SU-E-I-40: Phantom Research On Monochromatic Images Taken by Dual CBCT with Multiple Energy Sets

Abstract

Purpose: To evaluate the quality of monochromatic images at the same virtual monochromatic energy using dual cone-beam computed tomography (CBCT) with either kV/kV or MV/kV or MV/MV energy sets. Methods: CT images of Catphan 504 phantom were acquired using four different KV and MV settings: 80kV, 140kV, 4MV, 6MV. Three sets of monochromatic images were calculated: 80kV-140kV, 140kV-4MV and 4MV-6MV. Each set of CBCT images were reconstructed from the same selected virtual monochromatic energy of 1MeV. Contrast-to-Noise Ratios (CNRs) were calculated and compared between each pair of images with different energy sets. Results: Between kV/MV and MV/MV images, the CNRs are comparable for all inserts. However, differences of CNRs were observed between the kV/kV and kV/MV images. Delrin’s CNR ratio between kV/kV image and kV/MV image is 1.634. LDPE’s (Low-Density Polyethylene) CNR ratio between kV/kV and kV/MV images is 0.509. Polystyrene’s CNR ratio between kV/kV image and kV/MV image is 2.219. Conclusion: Preliminary results indicated that the CNRs calculated from CBCT images reconstructed from either kV/MV projections or MV/MV projections for the same selected virtual monochromatic energy may be comparable.

Authors:
 [1];  [2];  [3];  [1];  [4]; ;  [5]
  1. Duke University, Durham, NC - North Carolina (United States)
  2. (China)
  3. Shandong University, Jinan, Shandong (China)
  4. The Affiliated Cancer Hospital of Zhengzhou University, Zhengzhou, Henan (China)
  5. Duke University Medical Center, Durham, NC (United States)
Publication Date:
OSTI Identifier:
22493997
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; COMPUTERIZED TOMOGRAPHY; IMAGES; MONOCHROMATIC RADIATION; PHANTOMS; POLYETHYLENES; POLYSTYRENE

Citation Formats

Gao, R, Shandong University, Jinan, Shandong, Wang, H, Zhang, Y, Mao, R, Ren, L, and Yin, F. SU-E-I-40: Phantom Research On Monochromatic Images Taken by Dual CBCT with Multiple Energy Sets. United States: N. p., 2015. Web. doi:10.1118/1.4924037.
Gao, R, Shandong University, Jinan, Shandong, Wang, H, Zhang, Y, Mao, R, Ren, L, & Yin, F. SU-E-I-40: Phantom Research On Monochromatic Images Taken by Dual CBCT with Multiple Energy Sets. United States. doi:10.1118/1.4924037.
Gao, R, Shandong University, Jinan, Shandong, Wang, H, Zhang, Y, Mao, R, Ren, L, and Yin, F. Mon . "SU-E-I-40: Phantom Research On Monochromatic Images Taken by Dual CBCT with Multiple Energy Sets". United States. doi:10.1118/1.4924037.
@article{osti_22493997,
title = {SU-E-I-40: Phantom Research On Monochromatic Images Taken by Dual CBCT with Multiple Energy Sets},
author = {Gao, R and Shandong University, Jinan, Shandong and Wang, H and Zhang, Y and Mao, R and Ren, L and Yin, F},
abstractNote = {Purpose: To evaluate the quality of monochromatic images at the same virtual monochromatic energy using dual cone-beam computed tomography (CBCT) with either kV/kV or MV/kV or MV/MV energy sets. Methods: CT images of Catphan 504 phantom were acquired using four different KV and MV settings: 80kV, 140kV, 4MV, 6MV. Three sets of monochromatic images were calculated: 80kV-140kV, 140kV-4MV and 4MV-6MV. Each set of CBCT images were reconstructed from the same selected virtual monochromatic energy of 1MeV. Contrast-to-Noise Ratios (CNRs) were calculated and compared between each pair of images with different energy sets. Results: Between kV/MV and MV/MV images, the CNRs are comparable for all inserts. However, differences of CNRs were observed between the kV/kV and kV/MV images. Delrin’s CNR ratio between kV/kV image and kV/MV image is 1.634. LDPE’s (Low-Density Polyethylene) CNR ratio between kV/kV and kV/MV images is 0.509. Polystyrene’s CNR ratio between kV/kV image and kV/MV image is 2.219. Conclusion: Preliminary results indicated that the CNRs calculated from CBCT images reconstructed from either kV/MV projections or MV/MV projections for the same selected virtual monochromatic energy may be comparable.},
doi = {10.1118/1.4924037},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: In our clinic, the planning CT is used for definitive and boost low-dose-rate (LDR) brachytherapy treatments to determine the ultrasound volume in the operating room (OR) at the time of the implant. While the CT overestimation of OR volume is known, a larger estimation discrepancy has been observed for boost treatments. A possible reason is the prostate size reduction during EBRT for boost patients. Since cone-beam CT (CBCT) is often used as routine imaging guidance of EBRT, this prostate volume change may be captured. This study investigates if CBCT taken during EBRT includes the volume change information and thereforemore » beats CT in estimating the prostate OR volumes. Methods: 9 prostate patients treated with EBRT (45Gy in 1.8Gy per fractions to the whole pelvis) and I-125 seed implants (108Gy) were involved in this study. During EBRT, CBCT image guidance was performed on a weekly basis. For each patient, the prostate volumes on the first and the last available CBCT images were manually contoured by a physician. These volumes were then compared to each other and with the contoured volumes from the planning CT and from the ultrasound images in the OR. Results: The first and the last CBCT images did not show significant prostate volume change. Their average +/− standard deviation of prostate volumes were 24.4cc+/−14.6cc and 29.9cc+/−16.1cc, respectively (T-test p=0.68). The ratio of the OR volume to the last CBCT (0.71+/−0.21) was not significantly different from the ratio of OR volumes to the planning CT (0.61+/−0.13) (p=0.25). Conclusion: In this study, CBCT does not show significant prostate volume changes during EBRT. CBCT and CT volumes are quite consistent and no improvement of volume estimation using CBCT is observed. The advantage of CBCT as a replacement of CT for volume study of boost LDR brachytherapy is limited.« less
  • Purpose: To investigate the effects of scanning parameters and respiratory patterns on the image quality for 4-dimensional cone-beam computed tomography(4D-CBCT) imaging, and assess the accuracy of computed tumor trajectory for lung imaging using registration of phased 4D-CBCT imaging with treatment planning-CT. Methods: We simulated a periodic and non-sinusoidal respirations with various breathing periods and amplitudes using a respiratory phantom(Quasar, Modus Medical Devices Inc) to acquire respiration-correlated 4D-CBCT images. 4D-CBCT scans(Elekta Oncology Systems Ltd) were performed with different scanning parameters for collimation size(e.g., small and medium field-of-views) and scanning speed(e.g., slow 50°·min{sup −1}, fast 100°·min{sup −1}). Using a standard CBCT-QA phantom(Catphan500,more » The Phantom Laboratory), the image qualities of all phases in 4D-CBCT were evaluated with contrast-to-noise ratio(CNR) for lung tissue and uniformity in each module. Using a respiratory phantom, the target imaging in 4D-CBCT was compared to 3D-CBCT target image. The target trajectory from 10-respiratory phases in 4D-CBCT was extracted using an automatic image registration and subsequently assessed the accuracy by comparing with actual motion of the target. Results: Image analysis indicated that a short respiration with a small amplitude resulted in superior CNR and uniformity. Smaller variation of CNR and uniformity was present amongst different respiratory phases. The small field-of-view with a partial scan using slow scan can improve CNR, but degraded uniformity. Large amplitude of respiration can degrade image quality. RMS of voxel densities in tumor area of 4D-CBCT images between sinusoidal and non-sinusoidal motion exhibited no significant difference. The maximum displacement errors of motion trajectories were less than 1.0 mm and 13.5 mm, for sinusoidal and non-sinusoidal breathings, respectively. The accuracy of motion reconstruction showed good overall agreement with the 4D-CBCT image quality results only using sinusoidal breathings. Conclusion: This information can be used to determine the appropriate acquisition parameters of 4D-CBCT imaging for registration accuracy and target trajectory measurements in a clinical setting.« less
  • Purpose: To acquire upright CBCT images using the onboard imager of a Varian TrueBeam. An easy to implement upright imaging protocol could allow for widespread upright radiation therapy which would greatly benefit certain patients. These include thoracic cancer patients (because lung volume increases in a seated position) and patients who experience substantial discomfort during supine treatment. Methods: To acquire upright CBCT images, the gantry head remained stationary at 0 degrees with the KV imager arms extended to their lateral positions. Phantoms were placed upright at the end of the treatment couch. During a scan, the couch rotated from 270 tomore » 90 degrees while continuous fluoroscopic projections were taken by the onboard imager. To extend the field-of-view, this sequence was performed twice: once with the KV detector longitudinally offset +14.5cm and once with it longitudinally offset −14.5cm. The resulting two image sets were stitched together before reconstruction. The imaging beam parameters were chosen to deliver a dose similar to that given during a simulation CT. Image quality was evaluated for spatial linearity, high and low contrast resolution, and HU linearity using CatPhan and anthropomorphic phantoms. A deformable registration technique was used to evaluate HU mapping from a simulation CT. Results: Spatial linearity and high contrast resolution were maintained in upright CBCT when compared to simulation CT. However, low contrast resolution and HU linearity degraded. Streak artifacts were caused by the limited 180 degree arc of the couch, and the stitching process created a sharp artifact at the center of the reconstruction. The deformable registration was robust in the HU mapping even with these artifacts and the loss of HU linearity. Conclusions: The image quality obtained from upright CBCT was sufficient for treatment planning. The success of this novel technique is an important step towards a future clinical protocol. This project was funded in part by Varian Medical Systems, Inc.« less
  • Purpose: Our previous study showed that weekly dose monitoring using cone-beam CT (CBCT) images can guide the timing and need for adaptive re-planning during the treatment of head and neck (HN) cancer. Here we aim to confirm the dosimetric improvement of adaptive radiotherapy (ART) using weekly CBCTs. Methods: We randomly selected seven HN patients treated with ART due to noticeable anatomic changes. Twenty weekly images acquired during the second treatment course were included. These CBCTs were aligned with both the initial and re-planning simulation CTs according to the clinical shifts. Daily doses were re-calculated for both the initial and adaptivemore » plans. Contours of the tumor and organs-at-risk (OARs) were manually delineated by a physician on the re-planning CT and then were transferred to the CBCTs for plan evaluation. Contour modifications were made based on the daily anatomic changes observed on CBCTs. All patients were treated with 70Gy to the primary tumor and 56Gy to the elective lymph nodes. Results: Volumetric changes of the tumor (range — 43.9%∼+15.9%) were observed. The average D99 to the primary tumor was (70.1±2.0)Gy (range 62.2∼72.5Gy) for the adaptive plan and (66.0±5.5)Gy (range 50.9∼70.7Gy) for the initial plan(p<<0.01). The average D99 to the elective neck was (56.3±1.3)Gy (range 52.8∼59.2Gy) for the adaptive plan and (52.4±7.0)Gy (range 37.7∼58.6Gy) for the initial plan(p=0.01). The parotid decreased in volume during the treatment course (range 7.3%∼42.2%). The average D-mean to the spared parotid decreased by 15.3% (p=0.002) for the adaptive plan when compared to the original. With ART, 4 out of 7 patients experienced better sparing of the spinal cord (D-max reduced by 2.5%∼10.2%) and the oral cavity (D-mean reduced by 3.5%∼20.1%). Conclusion: Weekly CBCT dosimetry confirms that ART is an effective method to accommodate on-treatment anatomic changes. In select patients, tumor coverage and OAR sparing may be improved with ART. Research is funded by Siemens.« less
  • Purpose: Deformable image registration (DIR) is used routinely in the clinic without a formalized quality assurance (QA) process. Using simulated deformations to digitally deform images in a known way and comparing to DIR algorithm predictions is a powerful technique for DIR QA. This technique must also simulate realistic image noise and artifacts, especially between modalities. This study developed an algorithm to create simulated daily kV cone-beam computed-tomography (CBCT) images from CT images for DIR QA between these modalities. Methods: A Catphan and physical head-and-neck phantom, with known deformations, were used. CT and kV-CBCT images of the Catphan were utilized tomore » characterize the changes in Hounsfield units, noise, and image cupping that occur between these imaging modalities. The algorithm then imprinted these changes onto a CT image of the deformed head-and-neck phantom, thereby creating a simulated-CBCT image. CT and kV-CBCT images of the undeformed and deformed head-and-neck phantom were also acquired. The Velocity and MIM DIR algorithms were applied between the undeformed CT image and each of the deformed CT, CBCT, and simulated-CBCT images to obtain predicted deformations. The error between the known and predicted deformations was used as a metric to evaluate the quality of the simulated-CBCT image. Ideally, the simulated-CBCT image registration would produce the same accuracy as the deformed CBCT image registration. Results: For Velocity, the mean error was 1.4 mm for the CT-CT registration, 1.7 mm for the CT-CBCT registration, and 1.4 mm for the CT-simulated-CBCT registration. These same numbers were 1.5, 4.5, and 5.9 mm, respectively, for MIM. Conclusion: All cases produced similar accuracy for Velocity. MIM produced similar values of accuracy for CT-CT registration, but was not as accurate for CT-CBCT registrations. The MIM simulated-CBCT registration followed this same trend, but overestimated MIM DIR errors relative to the CT-CBCT registration.« less