CT Imaging System Research Articles

Contrôle qualité d’un système d’imagerie cone beam mégavoltage

Purpose This paper presents the development of a protocol for quality control of a megavoltage cone beam CT imaging system (MVCB) mounted on a Siemens Oncor 6 MV linear accelerator. Materials and methods Several parameters were controlled on the MVCB system: (1) the initial geometric calibration of the system; (2) the quality of the images (geometric distortion, uniformity, spatial resolution, low contrast resolution) for various protocols; (3) the correspondence between the intensity of voxels and electronic densities; (4) the dose delivered when achieving a MVCB. These tests were done mainly with two cylindrical phantoms specific to the quality control (QC) of a MVCB system, supplied by Siemens, and with the Catphan 600 phantom (The Phantom Laboratory) and Quasar™ Multipurpose Body phantom (Modus Medical Devices Inc). Results The results of the quality control of the images were within the tolerances. The use of the Catphan 600 phantom was inadequate for the QC of MVCB images. These tests also highlighted the need to correct the MVCB images for the “cupping artefact” for dose calculation purpose. Conclusion The initial characteristics of the MVCB imaging system were established. Such testing also provided the assessment of the influence of various parameters on the image quality as well as the associated dose delivered during their acquisition, and emphasized the corrections needed to use MVCB images for dose calculation.

TH‐C‐350‐10: Improving Accuracy of Electron Density Measurement in the Presence of Metallic Implants Using Orthovoltage Computed Tomography

Purpose: To evaluate the improvement in electron density measurement and metal artifact reduction using orthovoltage computed tomography (OVCT) imaging compared with conventional kilovoltage CT (KVCT). Method and Materials: We constructed a bench‐top CT imaging system with adjustable x‐ray tube voltage up to 320 kVp. A commercial tissue‐characterization phantom loaded with various tissue substitute inserts and two metal inserts — Titanium (Ti) and Aluminum (Al) were scanned using 125 kVp (KVCT) and 320 kVp (OVCT) x‐rays, respectively. The metal artifacts are evaluated in two ways — visually in the constructed axial CT image and by the deviation of estimated electron density from true electron density for uniform materials outside the metal. The stoichiometric calibration curves were obtained for both KVCT and OVCT imaging system by following the Schneider method. Results: The metal streak artifacts are seen to be reduced significantly in OVCT image than in KVCT image, especially in the area near Ti insert. The deviation of estimated electron density for the materials outside the metal are also reduced significantly by using OVCT than by using KVCT: from 42% (maximum) and 18% (root‐mean‐square) to 12% and 2.0% for heavy artifact area, and from 12% (MAX) and 3.0% (RMS) to 6.3% and 1.4% for light artifact area, respectively. The relationships between CT numbers (Hounsfield Unit) and relative electron densities (to water) are more predictable for both tissue substitutes and real biological tissues using OVCT than using KVCT. Unlike KVCT, the calibration curve for OVCT is insensitive to the tissue substitutes selected for direct electron density calibration. Conclusion: OVCT may be a good option for high precision radiotherapy treatment planning, especially for patients with metal implants and especially for charged particle therapy, such as proton therapy. Conflict of Interest: Collaborated with Varian Medical Systems.

SU‐GG‐J‐173: Study of CT Number Dependence On Hardware Settings and Post Image Processing in Micro CT Systems

Purpose: In recent years, micro CT systems have been emerged as a promising imaging modality for small animal model study. We report our efforts in the research investigation on the variations of CT numbers at various hardware and software settings in a commercial micro CT scanner as CT numbers are crucial to some imaging applications such as the bone mineral density evaluation. Method and Materials: In this work, a commercial micro CT imaging system (SkyScan 1076) was used to acquire the projection images. A modified Feldkamp reconstruction method was integrated in the scanner. Four different phantoms including lung, adipose, muscle, and bone were imaged at various energy values and then CT numbers were calculated at the mid plane of the phantoms. Different metallic filters in the x‐ray tube unit were used in the study. We also implemented two major image artifact reduction techniques (beam hardening and ring artifacts) and studied how those post image processing would effect the CT numbers. Results: The variability in CT numbers for different filters was −800 to −600 HU in lung phantom, −300 to −150 HU in adipose phantom, +20 to +70 HU in muscle phantom, and +1000 to +3000 in bone phantom. Meanwhile, the CT number variations ranged from +1000 to +4000 for the bone phantom when beam hardening reduction algorithm was applied. Conclusion: We have conducted a series of study for the variations in CT numbers computed from images acquired from a commercial micro CT imager at various hardware and software settings. Four uniform phantoms designed for the micro CT systems with known materials and densities were used. Imaging parameters included the x‐ray imaging energies, filters, and software settings. Accurate CT numbers are important and critical to the quantification applications such as the bones density calculations and tissue characterization.

SU‐GG‐J‐127: Micro CT Imaging Evaluation for the Scaffold‐Guided Calvarial Bone Defects Repair in Small Animal Models

Purpose: In recent years, micro CT imaging systems have been emerged as a promising imaging technique for the tissue engineering applications. We report our research results in using a commercial micro CT imager to evaluate the bone defect repair in small animals. Method and Materials: In this study, the animal model included Fischer 344 female rats. The surgery was performed at the top calvarial area and a circular‐shaped hole with diameter of 8.0 mm was cut out. Human mesenchymal stem cells with a baculovirus expressing BMP‐2 were engineered and implanted in the biodegradable scaffolds. These scaffolds were fabricated from polymers and then attached to the critical‐size area in the rats. In the experiments, there were three imaging groups including a control group for comparisons. A period of 12 weeks was scheduled to complete the micro CT imaging experiments. The imaging modality was a commercial SkyScan 1076 micro CT system. Mathematical methods, including density slice technique, were applied to quantify the bone regeneration progress. Results: Based on our preliminary analysis from the volumetric images reconstructed from the micro CT projections, significant mineralization can be detected at week four and full bony bridging in the critical‐size areas can be observed at week 12. The images were acquired at the settings of 80 kVp for the x‐ray energy, 124 μA for the current, 316 ms for the exposure time, and 360 projections for one full circular rotation. Conclusion: We have succeeded in using the micro CT imaging technique to quantify the scaffold‐guided bone repair progress in a small animal model. Our images showed that the full bony bridging can be observed at the week of 12. The results indicated that the feasibility of future potential clinical applications of baculovirus‐engineered mesenchymal stem cells in human bone regeneration.

SU-GG-J-44: Carbon Nanotube Field Emission Technology Enables Novel Imaging and Irradiation System Development for Cancer Research and Clinical Application

Purpose:Carbon nanotubefield emission is an emerging nanotechnology for novel x‐ray imaging and radiation delivery systems development for cancer research and clinical application. In this presentation we will give a general review of the nanotechnology and its applications in the development of novel devices including CT imaging,tomosynthesis, and cancer research radiation delivery systems. Method and Materials:Carbon nanotubefield emission is a based on the unique properties of a nanomaterial called carbon nanotubes(CNT).CNT is the newest carbon allotrope discovered in 1991 and it is comprised of either a single graphene shell, called the single‐wall carbon nanotube, or multiple concentric graphene shells termed a multi‐wall carbon nanotube. The signature feature is a very large aspect ratio (ratio of diameter to length) that is typically is on the order 103. The high aspect ratio makes CNTs a practical and excellent field emitter that can produce high current density with intrinsically small divergence and extremely high temporal resolution. More importantly, its unprecedented flexibility in cathode design has launched new creativity in imaging and therapy system development. Results: We will show examples of our research development on CNTfield emission based imaging and irradiation systems that include 4D micro‐RT, stationary tomosynthesis, multi‐pixel electron microbeam cellular irradiator under real time microscope observation, and multi‐pixel x‐ray micro‐CT‐RT image‐guided and intensity‐modulated radiation for small animal tumor models. The technical challenges of the CNTfield emissiontechnology will also be discussed. Conclusion:Carbon nanotubefield emissiontechnology has shown great promise in developing novel imaging and radiation systems that can potentially advance cancer research and improve the quality and efficiency of cancer diagnosis and treatment.

TH‐C‐AUD C‐08: Moving Towards Real Time Adaptive Radiation Therapy: Integrating Patient Imaging, Plan Adaptation and Radiation Delivery

Purpose: To propose a new approach to on‐line adaptive radiation therapy (ART) in which daily image acquisition, plan adaptation and radiation delivery are performed concurrently. Method and Materials: Daily imaging was performed using an on‐board cone beam CT imaging system. X‐ray projections were continuously acquired as the gantry rotates between treatment positions. A filtered back‐projection algorithm was used to reconstruct 3D digital tomosynthesis (DTS) images from the limited angle x‐ray projection data. An edge detection algorithm was used to automatically segment the 3D DTS images as the gantry arrives at each treatment position. The treatment plan was then re‐optimized for the most recent DTS image contours using modified direct aperture optimization (DAO). To test our system, a model representing an average prostate case was generated. A treatment plan based on this original anatomy was created using our DAO system. To simulate inter‐fractional prostate deformations, three clinically relevant deformations (labeled: small, medium and large) were modeled by systematically deforming the original anatomy. The ability of our integrated approach to adapt the original treatment plan to account for the anatomy deformations was investigated. Results: The original treatment plan becomes clinically unacceptable for all three deformations, based on the dose‐volume constraints from the Radiotherapy and Oncology Group 0415 prostate protocol. Using our integrated approach to on‐line ART, the original treatment plan was successfully adapted to arrive at a clinically acceptable plan for all three anatomy deformations, with the treatment time drastically reduced compared to the current on‐line ART procedure. Conclusion: We have developed a new approach to on‐line ART in which image acquisition, plan adaptation and radiation delivery are temporally integrated. We have shown that it can successfully adapt the original treatment plan for three clinically relevant prostate deformations while considerably reducing treatment time.

SU‐EE‐A3‐03: Comparison of CBCT and Electromagnetic Transponders for Prostate Localization

Purpose: In prostate cancer radiotherapy, it is unknown how large the PTV margins must be to account for the isocenter correction tolerance and intrafraction motion. The risk of geographic miss can be minimized by the placement of fiducial markers in the prostate gland for daily pretreatment localization and adjustment of patient position if necessary. In this study, we assess the magnitude of interfraction and intrafraction isocenter displacement using implanted electromangnetic transponders, and validate the accuracy of interfraction localization using cone beam CT. Method and Materials: Fifteen supine prostate IMRT patients with three implanted transponders each were studied. Initial daily localization was based on three laser and skin marks. Daily localization error distribution was determined from offsets between the initial setup position and that determined by Calypso. Post setup with the Calypso system, isocenter localization was immediately independently verified by imaging the radio‐opaque transponders using an integrated cone beam CT imaging system. Both localization techniques produced lateral, longitudinal, and vertical target offsets from machine isocenter. Organ motion or patient movement during treatment was continuously monitored by the Calypso system at a 4‐mm threshold. Results: The mean interfraction displacement (± SD) in cm in the lateral, vertical, and longitudinal directions were −0.2 ± 0.6, 1.8 ± 1.3, and 0.3 ± 0.9, respectively. After any necessary isocenter corrections, the mean isocenter placement error relative to the cone beam CT (± SD) in cm in the lateral, vertical, and longitudinal directions were 0.0 ± 0.1, 0.1 ± 0.2, and 0.0 ± 0.1, respectively. Conclusion: Compared with use of skin marks, electromagnetic isocenter repositioning provides an increased degree of isocenter localization. Good agreement was observed between cone beam CT isocenter localization and electromagnetic repositioning. However, the electromagnetic technique, with real time continuous tracking, has the added advantage of threshold‐based intervention with no additional radiation dose.

Differences between Fluorescent and Bioluminescent Measurement for Optical Tomography Image Reconstruction in a Simultaneous PET and Optical CT Imaging System

Differences between Fluorescent and Bioluminescent Measurement for Optical Tomography Image Reconstruction in a Simultaneous PET and Optical CT Imaging System

Patient dose considerations for routine megavoltage cone‐beam CT imaging

Megavoltage cone-beam CT (MVCBCT), the recent addition to the family of in-room CT imaging systems for image-guided radiation therapy (IGRT), uses a conventional treatment unit equipped with a flat panel detector to obtain a three-dimensional representation of the patient in treatment position. MVCBCT has been used for more than two years in our clinic for anatomy verification and to improve patient alignment prior to dose delivery. The objective of this research is to evaluate the image acquisition dose delivered to patients for MVCBCT and to develop a simple method to reduce the additional dose resulting from routine MVCBCT imaging. Conventional CT scans of phantoms and patients were imported into a commercial treatment planning system (TPS: Phillips, Pinnacle) and an arc treatment mimicking the MVCBCT acquisition process was generated to compute the delivered acquisition dose. To validate the dose obtained from the TPS, a simple water-equivalent cylindrical phantom with spaces for MOSFETs and an ion chamber was used to measure the MVCBCT image acquisition dose. Absolute dose distributions were obtained by simulating MVCBCTs of 9 and 5 monitor units (MU) on pelvis and head and neck patients, respectively. A compensation factor was introduced to generate composite plans of treatment and MVCBCT imaging dose. The article provides a simple equation to compute the compensation factor. The developed imaging compensation method was tested on routinely used clinical plans for prostate and head and neck patients. The quantitative comparison between the calculated dose by the TPS and measurement points on the cylindrical phantom were all within 3%. The dose percentage difference for the ion chamber placed in the center of the phantom was only 0.2%. For a typical MVCBCT, the dose delivered to patients forms a small anterior-posterior gradient ranging from 0.6 to 1.2 cGy per MVCBCT MU. MVCBCT acquisitions in the pelvis and head and neck areas deliver slightly more dose than current portal imaging but render soft tissue information for positioning. Overall, the additional dose from daily 9 MU MVCBCTs of prostate patients is small compared to the treatment dose (<4%). Dose-volume histograms of compensated plans for pelvis and head and neck patients imaged daily with MVCBCT showed no additional dose to the target and small increases at low doses. The results indicate that the dose delivered for MVCBCT imaging can be precisely calculated in the TPS and therefore included in the treatment plan. This allows simple plan compensations, such as slightly reducing the treatment dose, to minimize the total dose received by critical structures from daily positioning with MVCBCT. The proposed compensation factor reduces the number of MU per treatment beam per fraction. Both the number of fractions and the beam arrangement are kept unchanged. Reducing the imaging volume in the cranio-caudal direction can further reduce the dose delivered for MVCBCT. This is a useful feature to eliminate the imaging dose to the eyes or to focus on a specific region of interest for alignment.

Organ doses from prostate radiotherapy and associated concomitant exposures

In addition to the therapeutic exposure, a course of radiotherapy will involve the additional (concomitant) irradiation of the patient using CT, simulator or portal imaging systems, for localization of the target volume and subsequent verification of treatment delivery. The number of concomitant exposures is likely to increase as the developing technical capabilities for conformal, image-guided radiotherapy make target and critical organ definition an increasingly important aspect of radiotherapy. Estimation of doses and risks to critical organs in the body from all sources is thus necessary to provide the basis for adequate justification of the exposures as required by ICRP. In this paper, doses to selected organs and tissues for which ICRP have identified fatal cancer probabilities have been measured using a realistic anthropomorphic phantom loaded with thermoluminescent dosemeters and irradiated using a treatment protocol for radical radiotherapy of the prostate. Independently, doses to the same organs and tissues have been measured from concomitant CT and portal imaging exposures given for localization and verification purposes. Although negligible in comparison with the target dose, realistic numbers of concomitant exposures give a small but significant contribution to the total dose to most organs and tissues outside the target volume. Generally, this is in the range 5-10% of the total organ dose, but can be as high as 20% for bone surfaces. These data may be used to estimate concomitant doses from any combination of CT and portal imaging and may help in the justification process, especially when additional verification exposures may be required during treatment.

Investigation of C‐Arm Cone‐Beam CT‐Guided Surgery of the Frontal Recess

A cone-beam CT (CBCT) imaging system based on a mobile C-arm (Siemens PowerMobil) incorporating a high-performance flat-panel detector (Varian PaxScan) has been developed in our laboratory. We hypothesize that intraoperative C-arm CBCT provides image quality and guidance performance sufficient to assist surgical approach to the frontal recess. A preclinical prospective study was conducted using six cadaver heads to assess the performance characteristics and the potential clinical utility of this imaging system. The mobile C-arm was employed for intraoperative CBCT guidance of the endoscopic approach to twelve frontal recesses. The imaging system is capable of sub-mm 3D spatial resolution with bone and soft-tissue visibility and a field of view sufficient for guidance of head and neck surgery. The system can generate intraoperative, volumetric CT images rapidly with an acceptably low radiation exposure to the patient and with image quality sufficient for most surgical tasks. Moreover, the system is portable and compatible with the surgical setup, providing excellent access to the patient. Finally, the accuracy of the system is not bound to a registration process. The ability to create updated images as surgery progresses introduces the concept of 'near-real-time' CT guidance for head and neck surgery. We found that the use of CBCT increased surgical confidence in accessing the frontal recess, resolved ambiguities with anatomical variations, and provided valuable teaching information to surgeons in training in both preoperative planning and correlation between tri-planar CT scans and intraoperative endoscopic findings.

Images of biological soft tissue using synchrotron X-ray and laser CT systems

Images of embedded biological soft tissue of snail are obtained using synchrotron X-ray and laser CT systems. The biological soft tissue is embedded in another object and the microstructure is non-uniformly distributed. Under such conditions, the clear identification and occupation of the embedded biological soft tissue is necessary. In order to improve the monochromacy and image quality, the Synchrotron Radiation for Medical Physics facility at Elettra, Trieste, Italy, has been used for the image acquisition. A similar study is performed with a novel trans-illumination laser CT imaging system using optical fiber based on the optical heterodyne detection method for biomedical use. Based on the experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the trans-illumination mode, similar to X-ray CT. Finally, images are presented, acquired using the two systems and the importance of these imaging techniques to image the internal structure of the embedded biological soft tissue is discussed.

Patient dosimetry in radionuclide therapy: the whys and the wherefores

The importance and methodology of contemporary patient dosimetry in well-established radionuclide therapies are reviewed. The different protocols used for radioiodine treatment of thyrotoxicosis are discussed. Special attention is paid to patient dosimetry in the largest safe dose approach for curative radioiodine therapy of thyroid remnants and metastases in the post-surgical treatment of differentiated thyroid cancer. Nowadays, meta-[131I]iodobenzylguanidine (131I-MIBG) therapy for neuroblastoma relies on bone marrow dose levels. Issues related to whole-body and tumour dosimetry in this type of radionuclide therapy, where, traditionally, dosimetry has played an important role, are discussed. A relatively large number of patients are treated with radiolabelled Lipiodol for hepatocellular carcinoma. Administered activities are restricted to 2.22 GBq (60 mCi) when using 131I-lipiodol because of the radioprotection measures to be taken. These radiation protection issues can be avoided by using 188Re labelled Lipiodol allowing further dose escalation. The follow-up of these patients also necessitates whole-body dosimetry. It is concluded that for treatment of malignant diseases reliable patient dosimetry is now a keystone of high quality radionuclide therapy. Where dosimetry of present medical applications focuses generally on the critical organs, in the near future accurate 3-dimensional tumour dosimetry also will become feasible by the introduction of the combined SPECT-CT and PET-CT imaging systems in the dosimetric methodology. This will allow treatment protocols based on tumour dose prescriptions as performed in external beam radiotherapy.

WE‐D‐I‐6B‐01: Soft Tissue Visualization Using a Highly Efficient Megavoltage Cone Beam CT Imaging System

Purpose: Recent developments in two‐dimensional x‐ray detector technology have made volumetric Cone Beam CT (CBCT) a feasible approach for integration with conventional medical linear accelerators. The requirements of a robust image guidance system for radiation therapy include the challenging combination of soft tissue sensitivity with clinically reasonable doses. Previously, low contrast objects have generally not been perceptible with MV energies due to relatively poor signal to noise ratio (SNR) performance. We have developed an improved imaging system that is optimized for MV CBCT and acquire CBCT images containing soft tissue contrast using a 6MV x‐ray beam. Method and Materials: Many factors, such as image noise, x‐ray scatter, improper calibration and acquisitions have a profound effect on the imaging performance of CBCT. In this study attempts were made to optimize these factors in order to maximize the SNR. A QC‐3V and contrast/resolution phantoms were used to determine the contrast to noise ratio (CNR) and f50 of a single 2‐D projection and the contrast and spatial resolution of the reconstructed images. Results: The computed f50 was 0.43 lp/mm and the CNR for a radiation dose of 0.02cGy was 43. Relative electron density as low as 1% can be resolved with clinically reasonable radiation doses. Clinical Megavoltage CBCT images acquired with this system demonstrate that anatomical structures such as the prostate and optic nerves are visible using radiation doses in range of 4 to 8cGy. Conclusion: We have developed an imaging system that is optimized for MV and acquire Megavoltage CBCT images containing soft tissue contrast using a 6MV x‐ray beam and irradiation doses in range of 4 to 8cGy. This system can also be used for routine portal imaging applications without risk of saturation for high dose/high energy treatment/verification imaging, or dosimetry applications. Conflict of Interest : Sponsored by Siemens.

A gated deep inspiration breath-hold radiation therapy technique using a linear position transducer

For patients with thoracic and abdominal lesions, respiration-induced internal organ motion and deformations during radiation therapy are limiting factors for the administration of high radiation dose. To increase the dose to the tumor and to reduce margins, tumor movement during treatment must be minimized. Currently, several types of breath-synchronized systems are in use. These systems include respiratory gating, deep inspiration breath-hold, active breathing control, and voluntary breath-hold. We used a linear position transducer (LPT) to monitor changes in a patient's abdominal cross-sectional area. The LPT tracks changes in body circumference during the respiratory cycle using a strap connected to the LPT and wrapped around the patient's torso. The LPT signal is monitored by a computer that provides a real-time plot of the patient's breathing pattern. In our technique, we use a CT study with multiple gated acquisitions. The Philips Medical Systems Q series CT imaging system is capable of operating in conjunction with a contrast injector. This allows a patient performing the deep inspiration breath-hold maneuver to send a signal to trigger the CT scanner acquisitions. The LPT system, when interfaced to a LINAC, allows treatment to be delivered only during deep inspiration breath-hold periods. Treatment stops automatically if the lung volume drops from a preset value. The whole treatment can be accomplished with 1 to 3 breath-holds. This technique has been used successfully to combine automatically gated radiation delivery with the deep inspiration breath-hold technique. This improves the accuracy of treatment for moving tumors, providing better target coverage, sparing more healthy tissue, and saving machine time. PACS numbers: 87.53.2j, 87.57.-s

Development of CT Imaging System with Very Low Energy Neutrons

Development of CT Imaging System with Very Low Energy Neutrons

A Transillumination CT Imaging System in Near-Infrared Regions with Optical Fiber Arrays

A Transillumination CT Imaging System in Near-Infrared Regions with Optical Fiber Arrays

Fundamental imaging properties of transillumination laser CT using optical fiber applicable to bio-medical sensing

We proposed and developed a novel transillumination laser CT imaging system, using optical fibers, based on the optical heterodyne detection method for biomedical use. The use of optical fibers enables portability and robustness against environmental changes such as varying temperature, air-flow shifts, and unexpected vibrations. In addition, motion-artifact-free images can be obtained with the present system as measurements can be performed with the object fixed. We experimentally investigate in detail the fundamental imaging properties of the system, that has a spatial resolution of 500 /spl mu/m, a dynamic range of approximately 110 dB, and a minimum-detectable-optical power of 10/sup -14/ W as a result of the excellent properties of the heterodyne detection. Based on experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the transillumination mode, similar to X-ray CT, at sub-millimeter spatial resolution and can derive quantitative information from the images. Finally, we experimentally demonstrate the first in-situ tomographic images of plants using the fiber-optic-based laser CT system.

Implementation of an on-board kilovoltage cone-beam CT imaging system for clinical applications

Implementation of an on-board kilovoltage cone-beam CT imaging system for clinical applications

35. X線CTと他のX線検査との被曝線量比較法の検討

35. X線CTと他のX線検査との被曝線量比較法の検討