Kilovoltage Research Articles

Effect of Change of Kilovoltage and Voxel Size on 3D Volume Measurement Using Cone Beam Computed Tomography

Purpose: The aim of this study is to study the impact of change in kilovoltage (KV) or voxel size on extracted 3D radiographic volume measurement of different sizes of endodontic files and to determine the optimal exposure parameters for volume measurement in CBCT. Methods: Eight different endodontic k files were radiographically exposed at three different kilovoltages using CBCT and divided into three groups, group 1 (80 KV ), group 2 (60 KV ), and group 3 (50 KV ), then exposed to two different voxel sizes, and divided into two groups, group a (300 μm) and group b (180 μm). The 3D radiographic volume and the actual files volumes were measured using ITK-SNAP software and water displacement method respectively. Finding: Regarding changes in the kilovoltages, no significant difference ( p ˃0.05 ) was reported between the mean of the 3D radiographic volume of groups 3 and 2 with the mean of actual volume with a mean difference of 1.1 ±7.7 mm3 and 2.6 ±9.6 mm3 respectively. The results for voxel size change, showed no significant difference between the mean of the 3D radiographic volume of group (b) and actual volume group with a mean difference of 1.9 ±7.8 mm3. In the other hand, the difference between the mean of volume measurement at group (a) and actual group became significant with a mean difference of 10.5 ±5.7 mm3 was found. Conclusion: it concluded that both changes in kilovoltage and voxel size parameters affect significantly the 3D volume measurement and reconstruction.

Exploratory models comparing ethiodized oil-glue and gold fiducials for bladder radiotherapy image-guidance.

Image-guidance with fiducials has been shown to improve pelvic radiotherapy outcome. However, bladder fiducials using ethiodized oil (EO) alone can disperse widely, and gold causes Computed Tomography scan (CT) metal artifacts. The study's purpose was to investigate the ability to deliver EO-tissue glue fiducials and compare them to gold for bladder radiotherapy image guidance. A fluid-filled porcine bladder model was used to assess the ability to cystoscopically inject visible EO glue fiducials into the submucosa. We then transferred the bladders into a porcine pelvis for imaging and compared them to gold fiducials using CT, Cone Beam CT (CBCT), and kilovoltage (KV) planar views. A tissue-equivalent phantom was utilized to analyze the CT number Hounsfield Unit (HU) characteristics and artifacts of the glue and gold fiducials. Percentile ranges and normal tissue voxel percentages of the subsequent CT number voxel histogram from a 2cm sphere surrounding the fiducial was used to characterize the artifact. We successfully delivered all EO glue fiducials into the porcine bladders as discrete fiducials. They were well seen on CT, CBCT, and KV imaging. The glue fiducials had lower CT number values, but less CT number spread of the voxel percentile ranges consistent with the diminished contrast and less artifact than gold. The glue fiducial types had similar CT number characteristics. This study has shown that EO glue fiducials can be delivered with online visualization qualities comparable to gold fiducials without metal-related artifacts.

Technical note: development and validation of a Monte Carlo tool for analysis of patient-generated photon scatter

Scattered radiation unavoidably generated in the patient will negatively impact both kilovoltage (KV) and megavoltage (MV) imaging applications. Recently, ‘hybrid’ methods (i.e. combining analytical and Monte Carlo (MC) techniques) are being investigated as a solution to accurately yet quickly calculate the scattered contribution for both KV and MV images. We have developed a customized MC simulation user code for investigating the individual components of patient-scattered photon fluence, which serves as a valuable tool in this area of research. The MC tool is based on the EGSnrc/DOSXYZnrc user code. The IAUSFL flag options associated with subroutine AUSGAB, combined with LATCH tracking, are used to classify the various interactions of particles with the media. Photons are grouped into six different categories: primary, 1st Compton scatter, 1st Rayleigh scatter, multiple scatter, bremsstrahlung, and positron annihilation. We take advantage of the geometric boundary check in DOSXYZnrc, to write exiting photon particle information to a phase-space file. The tool is validated using homogeneous and heterogeneous phantom configurations with monoenergetic and polyenergetic beams under parallel and divergent beam geometry, comparing MC-simulated exit primary fluence and singly-scattered fluence to corresponding analytical calculations. This MC tool has been validated to separately score the primary and scatter fluence components of the KV and MV imaging applications in the field of radiation therapy. The results are acceptable for the various configurations and beam energies tested here. Overall, the mean percentage differences are less than 0.2% and standard deviations less than 1.6%. This will be a critical test instrument for research in photon scatter applications and particularly for the development of hybrid methods, and is freely available from the authors for research purposes.

Fast kilovoltage (KV)-switching dual-energy computed tomography hydroxyapatite (HAP)-water decomposition technique for identifying bone marrow edema in vertebral compression fractures.

Hydroxyapatite (HAP) is the main component of bone mineral. The utility of using HAP-water decomposition technique with fast kilovoltage (KV)-switching dual-energy computed tomography (DECT) to detect abnormal edema in vertebral compression fractures (VCFs) has not been widely reported. A total of 31 consecutive patients with 80 VCFs who underwent DECT and magnetic resonance imaging (MRI) of the spine were retrospectively enrolled in our study between October 2018 and January 2019. VCFs in MR examinations served as the standard of reference. Two radiologists blindly and independently evaluated color-coded overlay virtual nonhydroxyapatite (VNHAP) images for the presence of abnormal edema. The inter-reader agreement, specificity, sensitivity, accuracy, and predictive values of VNHAP images for edema detection were calculated. The diagnostic accuracy of two readers was compared using McNemar's test. Two additional radiologists performed a quantitative analysis on VNHAP images, receiver operating characteristic (ROC) curve analysis was conducted, and the threshold was calculated. MRI depicted 45 edematous and 35 nonedematous VCFs. For visual analysis, the VNHAP technique showed a sensitivity of 93.3%, a specificity of 97.1%, a positive predictive value (PPV) of 97.7%, a negative predictive value (NPV) of 91.9%, and an accuracy of 95.0%. The inter-reader agreement was almost perfect (k=0.90). The diagnostic accuracy of the two readers showed no significant differences in the assessment of VNHAP images (P=1.00). Significant differences in CT numbers between vertebrae with and without bone marrow edema were found by quantitative analysis (P<0.01). The area under the curve (AUC) of the VNHAP images was estimated to be 0.917. The threshold of 1,003.2 mg/cm3 yielded a sensitivity of 88.9% and a specificity of 82.9% for the differentiation of fresh and old VCFs. Fast KV-switching DECT HAP-water decomposition technique had excellent diagnostic performance for identifying acute and chronic VCFs in visual and quantitative analyses.

Estimating intrafraction tumor motion during fiducial-based liver stereotactic radiotherapy via an iterative closest point (ICP) algorithm

BackgroundTumor motion may compromise the accuracy of liver stereotactic radiotherapy. In order to carry out a precise planning, estimating liver tumor motion during radiotherapy has received a lot of attention. Previous approach may have difficult to deal with image data corrupted by noise. The iterative closest point (ICP) algorithm is widely used for estimating the rigid registration of three-dimensional point sets when these data were dense or corrupted. In the light of this, our study estimated the three-dimensional (3D) rigid motion of liver tumors during stereotactic liver radiotherapy using reconstructed 3D coordinates of fiducials based on the ICP algorithm.MethodsFour hundred ninety-five pairs of orthogonal kilovoltage (KV) images from the CyberKnife stereo imaging system for 12 patients were used in this study. For each pair of images, the 3D coordinates of fiducial markers inside the liver were calculated via geometric derivations. The 3D coordinates were used to calculate the real-time translational and rotational motion of liver tumors around three axes via an ICP algorithm. The residual error was also investigated both with and without rotational correction.ResultsThe translational shifts of liver tumors in left-right (LR), anterior-posterior (AP),and superior-inferior (SI) directions were 2.92 ± 1.98 mm, 5.54 ± 3.12 mm, and 16.22 ± 5.86 mm, respectively; the rotational angles in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions were 3.95° ± 3.08°, 4.93° ± 2.90°, and 4.09° ± 1.99°, respectively. Rotational correction decreased 3D fiducial displacement from 1.19 ± 0.35 mm to 0.65 ± 0.24 mm (P<0.001).ConclusionsThe maximum translational movement occurred in the SI direction. Rotational correction decreased fiducial displacements and increased tumor tracking accuracy.

Helical image-guided stereotactic body radiotherapy (SBRT) for the treatment of early-stage lung cancer: a single-institution experience at the Willis-Knighton Cancer Center.

Our aim is to report on the clinical methods and outcomes of helical intensity-modulated stereotactic body radiotherapy (SBRT) for the treatment of early-stage non-small cell lung cancer (NSCLC). Seventy-nine patients with stage I NSCLC underwent helical SBRT with 48 Gy in 4 fractions or 60 Gy in 5 fractions. All patients underwent 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) or FDG-PET/computed tomography (CT) scanning in the immobilized treatment position for planned fusion with a separate kilovoltage (KV) CT simulation prior to treatment. Megavoltage CT images were obtained on the treatment unit prior to therapy and repeated at mid-fraction with comparison and fusion to the KV CT simulation planning images to assure setup accuracy. Serial follow-up with FDG-PET or FDG-PET/CT was performed at 3-4 months and every 6 months thereafter. Median follow-up was 27 months (range, 4-82 months). Overall local control rate (LCR) was 93.6% (95% confidence interval [CI], 86.0-97.3%) and 3-year overall survival (OS) was 58.4% (95% CI, 47.2-69.5%). For patients with T1N0M0 disease (n = 59) the LCR was 94.9% (95% CI, 86.1-98.3%) and the 3-year OS was 62.8% (95% CI, 49.9-73.9%). Patients treated with 60 Gy had longer 3-year OS than patients treated with 48 Gy (65.2% vs 37.5%; P = 0.044). SBRT-related toxicity was modest, with 10 patients developing grade 1/2 chest wall toxicity based on the Common Terminology Criteria for Adverse Events (CTCAE). Image-guided SBRT with helical IMRT delivered in 4 or 5 fractions of 12 Gy with rigid immobilization, FDG-PET-assisted targeting, and repeat mid-fraction CT scan is an effective treatment for early NSCLC.

Algorithm-enabled exploration of image-quality potential of cone-beam CT in image-guided radiation therapy

Kilo-voltage (KV) cone-beam computed tomography (CBCT) unit mounted onto a linear accelerator treatment system, often referred to as on-board imager (OBI), plays an increasingly important role in image-guided radiation therapy. While the FDK algorithm is currently used for reconstructing images from clinical OBI data, optimization-based reconstruction has also been investigated for OBI CBCT. An optimization-based reconstruction involves numerous parameters, which can significantly impact reconstruction properties (or utility). The success of an optimization-based reconstruction for a particular class of practical applications thus relies strongly on appropriate selection of parameter values. In the work, we focus on tailoring the constrained-TV-minimization-based reconstruction, an optimization-based reconstruction previously shown of some potential for CBCT imaging conditions of practical interest, to OBI imaging through appropriate selection of parameter values. In particular, for given real data of phantoms and patient collected with OBI CBCT, we first devise utility metrics specific to OBI-quality-assurance tasks and then apply them to guiding the selection of parameter values in constrained-TV-minimization-based reconstruction. The study results show that the reconstructions are with improvement, relative to clinical FDK reconstruction, in both visualization and quantitative assessments in terms of the devised utility metrics.

Radiotherapy dose calculation on KV cone‐beam CT image for lung tumor using the CIRS calibration

On-board kilovoltage (KV) cone-beam computed tomography (CBCT) images are used predominantly for the setup of patients' positioning. The image data can also potentially be used for dose calculation with the precise calibration of Hounsfield units (HU) to electron density (HU-density). CBCT calibration was analyzed in this study. A clinical treatment planning system was employed for CT and KV CBCT image to dose calculations and subsequent comparisons. Two HU-density tables were generated using the Computerized Imaging Reference Systems (CIRS) phantom. The results showed that a maximum ∼4% dose discrepancy was observed for inserts. The single field isodose curves were very close. The lung clinical patient study indicated that the volume of lung tumor that achieved the prescribed dose in CBCT was lower than in the CT plan. Our study showed that the dosimetric accuracy of CBCT-based dose calculation for lung tumor is acceptable only for the purpose of dosimetric checks with calibration applied. KV CBCT images cannot replace traditional CT images for dose calculation accuracy.

SU-D-103-01: TG 142 Imaging Modalities QA - Three Year Experience

Purpose: This study is initiated to check if the frequency of imaging QA suggested by AAPM Task Group Report 142(TG142) is necessary. TG142 presents recommendations for QA criteria of IGRT treatment. It is an update to AAPM TG40 and has added recommendations for imaging devices that are integrated with IGRT Linacs. The imaging devices studied include kilovoltage(KV) X-ray imaging, megavoltage(MV) portal imaging, and cone-beam CT(CBCT) with kV CBCT for Varian and MV CBCT for Siemens.Method and Materials: This study uses VarianIX2100 and Siemens Artiste Linacs to perform QAs on KV,MV,CBCT modalities. The QA was designed following under the recommendations of TG142. This study reports the daily imaging positioning/repositioning and imaging and treatment coordinate coincidence. QA results on kV, MV and CBCT from 4/7/2010∼12/14/2012 are analyzed. A radio opaque marker was implanted into the center of a 5cm cube. KV,MV,CBCT images are taken with the cube localized at the isocenter. Digital graticule is used in the software to verify the isocenter position. Another image is taken with the cube placed at 1cm superior, lateral and anterior of the isocenter. In-line fusion software is used to verify the contrived shift. Digital ruler provided at the on-board-imaging software or adaptive-targeting software was used to measure the position differences. The position differences were recorded at AP,LR,SI directions. Results: Thirty-two-month records on kV,MV,CBCT show the shifts in all three directions are within the tolerance of 1mm suggested in TG142 for stereotactic radiation treatment(SRS/SRT). There is no occasion where shifts are outside 1mm tolerance. Conclusions: The daily imaging QA suggested in TG142 is useful in ensuring the accuracy needed for SRS/SRT in IGRT. Thirty-two-month measurements presented suggest that decreasing the frequency of imaging QA may be acceptable, in particular for institutions reporting no violation of tolerance over periods of few years.

Stereotactic body radiation therapy for early-stage non-small-cell lung cancer utilizing a helical intensity modulated image-guided approach.

e17524 Background: To report the techniques and results of a large cohort of patients treated with stereotactic body radiotherapy (SBRT) for early-stage non-small-cell lung cancer (NSCLC) using image-guided helical intensity modulated radiation therapy (IMRT) and FDG-PET assisted targeting. Methods: Between February 2005 and August 2010, 79 patients with stage 1 NSCLC were treated with SBRT. 59 patients had T1 tumors and 20 patients had T2 tumors. 62 patients had biopsy proven malignancies and 17 patients were treated empirically based on strong clinical indications. Central tumor location did not disqualify patients. All patients underwent FDG-PET or FDG-PET/CT scanning in the treatment position for planned fusion with a separate kilovoltage (KV) CT simulation. Rigid immobilization was achieved during CT simulation using a double vacuum cast device with abdominal compression. SBRT was delivered via 12 Gy x 4 or 12 Gy x 5 fractionation scheme (48-60 Gy total). Megavoltage CT images were obtained on the treatment unit prior to therapy and repeated mid-fraction with comparison to the KV CT simulation planning images to assure set-up accuracy. Serial follow-up with FDG-PET or FDG-PET/CT studies were performed at 3 months and every 6 months thereafter on all surviving patients. Results: Median patient age was 73 years. Mean tumor size was 2.3 cm (range 0.5 – 6 cm). Median follow-up was 24 months (range 4-78 months). Overall local control rate (LCR) was 94% (95% confidence interval (CI), 86-97%) based on serial FDG-PET. LCR for T1 tumors was 95% vs. 90% for T2 tumors (p = 0.60). Entire cohort overall survival rate (OSR) was 87% (CI, 78-93%) at 1 year and 58% (CI, 47-68%) at 3 years. T1 patients had a 3-year OSR of 71% vs. 43% OSR for T2 patients (p = 0.04). No patients developed life threatening radiation pneumonitis or pulmonary complications. Chest wall pain or rib fracture was reported in 8 patients (10%; CI, 5-19%). Conclusions: Image-guided SBRT with helical IMRT delivered in 4 or 5 fractions of 12 Gy with rigid immobilization and FDG-PET assisted targeting is an effective treatment for early NSCLC and is associated with excellent local control rates and acceptable treatment-related morbidity.

Monitoring Dosimetric Impact of Weight Loss With Kilovoltage (KV) Cone Beam CT (CBCT) During Parotid-Sparing IMRT and Concurrent Chemotherapy

Parotid-sparing head-and-neck intensity-modulated radiotherapy (IMRT) can reduce long-term xerostomia. However, patients frequently experience weight loss and tumor shrinkage during treatment. We evaluate the use of kilovoltage (kV) cone beam computed tomography (CBCT) for dose monitoring and examine if the dosimetric impact of such changes on the parotid and critical neural structures warrants replanning during treatment. Ten patients with locally advanced oropharyngeal cancer were treated with contralateral parotid-sparing IMRT concurrently with platinum-based chemotherapy. Mean doses of 65 Gy and 54 Gy were delivered to clinical target volume (CTV)1 and CTV2, respectively, in 30 daily fractions. CBCT was prospectively acquired weekly. Each CBCT was coregistered with the planned isocenter. The spinal cord, brainstem, parotids, larynx, and oral cavity were outlined on each CBCT. Dose distributions were recalculated on the CBCT after correcting the gray scale to provide accurate Hounsfield calibration, using the original IMRT plan configuration. Planned contralateral parotid mean doses were not significantly different to those delivered during treatment (p > 0.1). Ipsilateral and contralateral parotids showed a mean reduction in volume of 29.7% and 28.4%, respectively. There was no significant difference between planned and delivered maximum dose to the brainstem (p = 0.6) or spinal cord (p = 0.2), mean dose to larynx (p = 0.5) and oral cavity (p = 0.8). End-of-treatment mean weight loss was 7.5 kg (8.8% of baseline weight). Despite a ≥10% weight loss in 5 patients, there was no significant dosimetric change affecting the contralateral parotid and neural structures. Although patient weight loss and parotid volume shrinkage was observed, overall, there was no significant excess dose to the organs at risk. No replanning was felt necessary for this patient cohort, but a larger patient sample will be investigated to further confirm these results. Nevertheless, kilovoltage CBCT is a valuable tool for patient setup verification and monitoring of dosimetric variation during radiotherapy.

A New Scatter Correction Method for KV and MV Cone Beam CT

Kilo-voltage(KV) and mega-voltage(MV) cone beam computed tomography (CBCT) play an important role in image-guided adaptive radiotherapy. However, the cupping effect, introduced by Compton scatter contribution due to a large cone angle of CBCT acquisition, significantly degrades the CBCT image quality and hampers its clinical application. The objective of this study is to develop a new CBCT scatter correction method in the image domain. The hypotheses of the proposed method are that the image intensity of different kind of materials in CBCT image should be globally uniform and the cupping effect can be described as a bias field, a low frequency signal across the whole 3-D images. Based on above assumptions, we proposed a maximum a posteriori probability (MAP) framework to estimate the bias field contribution. The well-known fuzzy C-mean model is extended to define the likelihood function of the CBCT image. A markov random field model is used to describe the prior probability of the mixture defined in FCM model. The bias field is characterized by a Gaussian prior probability with a banded covariance matrix representing a low-pass filter. An iterated conditional mode (ICM)-like approach is utilized to minimize the objective function. The corrected CBCT image can be obtained by subtracting the bias field from original CBCT image. The performance of correcting the cupping effect of CBCT image with the proposed MAP framework was tested using both contrast phantoms and clinical CBCT images. In the cylindrical shape-contrast phantom the higher density material is surrounded by the lower density material. In the contrast phantom study, the intensities of higher density material in both KV and MV CBCT images are even lower than that of lower density material due to the cupping effect. The corrected CBCT images showed almost same intensity distribution as the original contrast phantom images. In a real patient study, it is clearly shown that there is a shadow inside the brain soft tissue in the original brain KV and MV CBCT images. The corrected CBCT images significantly improved the uniformity of intensity distribution of brain soft tissue. The proposed image-based scatter correction method showed a promising result to reduce the cupping effect commonly encountered in KV and MV CBCT image.

A comparison of kilovoltage and megavoltage cone beam CT in radiotherapy

AbstractAs more and more patients are planned in 3D, the need to verify their position and treatment in 3D also becomes apparent. Megavoltage (MV) and kilovoltage (KV) cone beam computed tomography (CBCT) provide 3D verification of patient position. However, the soft tissue contrast and thus the accuracy of delineation is superior with KV CT imaging. CBCT in conjunction with energy fluence maps from electronic portal imaging devices (EPIDs) could theoretically be used to verify the dose delivered. In this instance, a cross calibration between the KV CBCT and the EPID would be required which would not be necessary with MV CBCT. Adaptive planning with CBCT poses similar challenges for both KV and MV CBCT. Although KV CBCT can produce images with Hounsfield units (HUs) comparable with conventional CT in homogenous phantoms there are large discrepancies in inhomogeneous mediums. If the cupping artefact is corrected for in MV CBCT, the HU values can compare well with KV CBCT for homogenous media. However, advances need to be made to achieve a lower patient dose with MV CBCT. At present, the lower dose required for KV CBCT allows for more frequent imaging and better image quality.

SU‐FF‐J‐80: Clinical Procedures for Daily Patient Setup Verification Using On‐Board Imager (OBI)

Purpose: The newly installed OBI system consists of a kilo‐voltage (KV) X‐ray source and a flat‐ panel detector mounted orthogonally to the megavoltage portal imager (MV) in Varian 21EX machine. These devices are linked to the OBI workstation which provides a platform for acquisition/analysis of images and auto couch motion for repositioning the patient. This paper presents our clinical procedures for patient setup verification using OBI. Method and Materials: In phase I, two sets of orthogonal MV/MV and KV/KV images were acquired to confirm the accuracy of the KV system by comparing daily KV images to traditional MV images and corresponding Digital Reconstructed Radiographs (DRRs). The phase II study acquired only one set of orthogonal MV/KV portal images for daily patient setup verification. An anterior MV and lateral KV images were obtained without gantry rotation. The OBI workstation provided the tools to match the images with DRRs and to analyze the shifts to be made for patient setup correction based on either implanted and/or anatomical markers. The treatment couch was moved automatically based on this analysis. Post‐shift MV/KV images were acquired to reconfirm patient positioning. All images and positioning data were electronically saved and reviewed. Results: Four prostate IMRT patients were included in phase I study. The isocenter alignment of the two sets of images (MV/MV and KV/KV) was found within 2mm relative to DRRs during the entire treatment courses. The phase II study included 30 prostate IMRT patients. The review of post‐shift MV/KV images showed an average of 2 mm deviation relative to DRRs. All procedures could be completed within 3–5 minutes. Conclusion: Phase I study proves that KV images are as reliable as MV portal images with better image quality. Phase II study verifies that matching/analysis tools and auto‐couch motion provide fast and accurate patient positioning.

SU‐FF‐J‐62: Image‐Guided Radiotherapy Feasibility Study Using Kilo‐Voltage Cone‐Beam CT Images for Patient Alignment Verification

Purpose: The objective of this work was to evaluate the feasibility to acquire the kilo‐voltage (KV) cone‐beam computer tomography (CBCT) images and to register the CBCT images with the conventional planning CT images for patient alignment verification. Method and Materials: A Varian high precision accelerator with on‐board KV imaging (OBI) system and CBCT was used in conjunction with a QA head phantom for patient setup position verification. In addition, the in‐house image registration and verification software was used for the analyses of patient alignment accuracy. First, we acquired the same reference image data sets of the QA head phantom from the CBCT and the LINAC/CT‐on‐rails unit. The conventional CT image set was used as the planning CT images. Applied the translation and/or the rotation to the QA head phantom to imitate the daily patient setup variation and then, acquired the daily CBCT images. Results: No differences were observed on the registration between the reference image sets obtained from the conventional planning CT and CBCT. Similar findings were also observed on the registration of the daily CBCT with the planning CT images when the translations were applied to the setup of the daily QA head phantom deviated from the planning QA head phantom setup. When the rotations were applied to the daily setup of the QA head phantom, the treatment target was registered well between the daily CBCT images and the planning CT images, but the difference of 1.3 mm was observed on the registration in the structure relatively far away from the target. Conclusion: Phantom studies indicated that the daily pretreatment CBCT images should be suitable to use for patient alignment verification with the planning CT images. Conflict of Interest: supported by Varian Medical Systems.

Field-based verified IMRT for prostate cancer using a newly developed dual kilovoltage (KV) on-board imager-evaluation of inter/intra-fraction motion and early clinical outcomes

Field-based verified IMRT for prostate cancer using a newly developed dual kilovoltage (KV) on-board imager-evaluation of inter/intra-fraction motion and early clinical outcomes

Daily megavoltage CT image guidance in the treatment of localized prostate cancer

Daily megavoltage CT image guidance in the treatment of localized prostate cancer

Field-based verified IMRT for prostate cancer using a newly developed dual kilovoltage (KV) on-board imager-evaluation of inter/intra-fraction motion and early clinical outcomes

A new on-board image-guided system has been design and implemented for the treatment of prostate cancer with Intensity Modulated Radiotherapy (IMRT). The aim of this study was to investigate the magnitude of organ motion uncertainty at setup and at intra-fraction. In addition, the effect of an intra-field reposition method and clinical outcomes were assessed.

Daily megavoltage ct imaging for lung cancer during a course of external beam radiotherapy with a helical tomotherapy device

Our aim was to study the process of daily megavoltage (MV) CT imaging for a pulmonary malignancy. We report our initial experience with a helical tomotherapy device. The initial 20 MVCT images obtained during a course of external beam radiotherapy with the Hi*Art system (Tomotherapy Inc.) were analyzed. The treatment was designed to treat a lesion in the upper right lung to a total of 68 Gy at 2 Gy per fraction. The current study is limited to the first 20 of a total planned 34 fractions. The treatment was designed with the clinical target volume (CTV) defined on exhale and inhale simulation kilovoltage (KV) CT studies. The images were fused with a free breathing CT, since the treatment was to be delivered with free shallow breathing. The fusion was based on the registration of the spinal cord. The maximum extent of the tumor among the three CT scans was used to determine the CTV. A 10 mm margin was used to determine the planning target volume. Daily MVCT images were acquired with the Hi*Art system with the patient in the treatment position. The spinal cord was used to align the daily MVCT images to the simulation KVCT image. Each day, the set-up errors were recorded and corrected by the radiation therapists by adjusting the position of the treatment couch. The treatment was subsequently delivered with the Hi*Art system. Tumor dimensions were later measured on the daily MVCT images in the superior/inferior, anterior/posterior, and lateral dimensions. The tumor volume was calculated using the tumor dimensions as the volume constituting an ellipsoid structure. Figure 1 displays a sample of the treated tumor’s simulation KVCT images, and a sample of the tumor’s MVCT images acquired at the time of the 20th treatment. These corresponding images were obtained after adjusting for set-up errors by aligning on the spinal cord. A clear response is observed with shrinkage of the tumor. The size of the tumor documented on a daily basis clearly decreased over the 20 fractions. Fig. 2 documents the reduction in the tumor volume to approximately half of its original size in 20 fractions. Megavoltage imaging can be useful in two ways in the process of treating of a pulmonary malignancy with radiotherapy. It can be used to adjust patient position by daily aligning the patient’s observed internal anatomy to the expected patient position, thereby eliminating set-up errors. In addition, it can be used to measure previously unobserved tumor response during a radiotherapy course. Tumor shrinkage within the first 20 days of therapy was documented with daily megavoltage imaging.

To Err With Air

To the Editor:— As to the relative value of the gas contrast technique and the high kilovoltage (KV) method for examination of the large bowel, much can be said on both sides, but what is said must be factual, objective, and unbiased. To advocate abandonment of one or the other of these methods would be radical indeed, yet this is what the author has recommended in regard to the contrast method. This recommendation is made in spite of the fact that both these techniques have been known for several decades and it is the double contrast technique that is the more widely used amongst radiologists, who by this time certainly have had an opportunity to investigate both sides of the situation and to make their free selection. One might expect then that if one were to advocate such a drastic step as abandonment of a procedure which the majority of