Cone-beam computed tomography noise reduction method based on U-Net with convolutional block attention module in proton therapy

Cone-beam computed tomography(CBCT) is mostly used for position verification during the treatment process. However,severe image artifacts in CBCT hinder its direct use in dose calculation and adaptive radiation therapy re-planning for proton therapy. In this study, an improved U-Net neural network named CBAM-U-Net was proposed for CBCT noise reduction in proton therapy, which is a CBCT denoised U-Net network with convolutional block attention modules. The datasets contained 20 groups of head and neck images. The CT images were registered to CBCT images as ground truth. The original CBCT denoised U-Net network, sCTU-Net, was trained for model performance comparison. The synthetic CT(SCT) images generated by CBAM-U-Net and the original sCTU-Net are called CBAM-SCT and U-Net-SCT images, respectively. The HU accuracies of the CT, CBCT, and SCT images were compared using four metrics: mean absolute error(MAE), root mean square error(RMSE), peak signal-to-noise ratio(PSNR), and structure similarity index measure(SSIM). The mean values of the MAE, RMSE, PSNR, and SSIM of CBAM-SCT images were 23.80 HU, 64.63 HU, 52.27 dB, and 0.9919, respectively,which were superior to those of the U-Net-SCT images. To evaluate dosimetric accuracy, the range accuracy was compared for a single-energy proton beam. The γ-index pass rates of a 4 cm × 4 cm scanned field and simple plan were calculated to compare the effects of the noise reduction capabilities of the original U-Net and CBAM-U-Net on the dose calculation results. CBAM-U-Net reduced noise more effectively than sCTU-Net, particularly in high-density tissues. We proposed a CBAM-U-Net model for CBCT noise reduction in proton therapy. Owing to the excellent noise reduction capabilities of CBAM-U-Net, the proposed model provided relatively explicit information regarding patient tissues. Moreover, it maybe be used in dose calculation and adaptive treatment planning in the future.

利用Cone-Beam CT探讨支抗微螺钉周围骨密度与其稳定性的关系

目的:利用Cone-Beam CT测量支抗微螺钉周围骨密度值,探讨其与微螺钉稳定性的关系。方法:选取颌骨左右对称植入微螺钉后一侧松动而另一侧稳固的7名(共18枚微螺钉)正畸患者。拍摄CBCT,所得三维影像重建后用OnDemand 3DApplication软件对微螺钉骨内部分周围2mm范围内骨密度(以Hounsfield Unit表示)进行测量,自身对照比较分析双侧对称部位所植入微螺钉周围骨密度测量值间的差异。结果:松动微螺钉与稳定微螺钉骨内部分周围2mm范围内骨密度无统计学差异,两侧微螺钉钉尖部1/3、钉中部1/3及钉颈部1/3周围骨密度均无统计学差异。结论:微螺钉种植支抗的稳定性与其周围骨密度间未发现明显相关性。

锥形术CT测量分析下颌第一磨牙拟种植区剩余牙槽嵴的骨量

背景:随着口腔领域的发展与进步,口腔种植技术逐渐成为替代传统义齿的主流选择。近年来,多种骨增量技术的成熟以及口腔数字化领域的不断发展,使种植适应证不断扩大,种植手术的成功率也越来越高。但是种植手术前使用锥形术CT对剩余牙槽嵴骨量进行准确测量并且个性化制定合适的种植方案,成为一部分临床医师的难题。目的:采用锥形束CT对下颌第一磨牙拟种植区剩余牙槽嵴骨量进行测量分析,为优化下颌第一磨牙区种植方案的设计提供参考。方法:采用回顾性研究设计,纳入205例下颌第一磨牙缺失患者的锥形术CT影像,测量下颌第一磨牙拟种植区剩余牙槽嵴高度及宽度,并将剩余牙槽嵴形态分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4类(Ⅱ、Ⅲ、Ⅳ类剩余牙槽嵴为骨量不足),统计分析下颌第一磨牙剩余牙槽嵴高度、宽度、形态频数分布,不同性别患者下颌第一磨牙剩余牙槽嵴高度和牙槽嵴顶宽度的差异,剩余牙槽嵴高度与剩余牙槽嵴顶宽度、剩余牙槽嵴底宽度的相关性,年龄与剩余牙槽嵴顶宽度、高度的相关性。结果与结论:①下颌第一磨牙拟种植区剩余牙槽嵴高度平均为(12.14±2.96)mm,其中<12 mm者占43.41%(89/205),下颌第一磨牙拟种植区牙槽嵴顶宽度平均为(6.80±1.65)mm,其中<6 mm者占26.34%(54/205);②男性下颌第一磨牙剩余牙槽嵴高度高于女性,但差异无显著性意义(P>0.05),男性下颌第一磨牙剩余牙槽嵴顶宽度宽于女性,差异有显著性意义(P<0.01);③剩余牙槽嵴高度与剩余牙槽嵴顶宽度和剩余牙槽嵴底宽度呈负相关(P<0.05);年龄与剩余牙槽嵴顶宽度呈正相关(P<0.05),与剩余牙槽嵴高度无明显相关性(P>0.05);④剩余牙槽嵴形态Ⅰ类占58.05%(119/205),Ⅱ类占9.27%(19/205),Ⅲ类占20.49%(42/205),Ⅳ类占12.19%(25/205),其中多数为Ⅲ类剩余牙槽嵴骨量不足,临床医生需要根据剩余牙槽嵴类型个性化设计最佳的种植方案。

Pulp health and calcific healing of a complicated crown–root fracture with additional root fracture in a maxillary incisor: A case report

BACKGROUND Complicated crown–root fracture (CRF) involves severe injury to the crown, root,and pulp, and may be accompanied by multiple root fractures. The loss of a toothhas lifelong consequences for children and teenagers, but the maintenance of pulphealth and the calcific healing of multiple root fractures are rarely reported in theliterature.CASE SUMMARY This case reports healing of a permanent tooth with complicated crown–root andadditional root fractures, in which pulp health was maintained. A 10-year-old girlfell and fractured the root of her maxillary left central incisor at the cervical level.After the coronal fragment was repositioned, the tooth was splinted until thetooth was no longer mobile, 2 years later. Eight years after treatment, the toothhas remained asymptomatic with vital pulp and localized gingival overgrowth.Cone-beam computed tomography revealed not only calcified healing of the CRFbut also spontaneous healing in an additional undiagnosed root fracture. Thefracture line on the enamel could not be healed by hard tissue and formed agroove in the cervical crown. It was speculated that the groove was related to thelocalized gingival overgrowth.CONCLUSION This case provides a clinical perspective of the treatment of a tooth with acomplicated CRF and an additional root fracture.

The Association between Lower Incisal Inclination and Morphology of the Supporting Alveolar Bone—A Cone-Beam CT Study

Aim To investigate the relationship between the positioning of the lower central incisor and physical morphology of the surrounding alveolar bone. Methodology Thirty-eight patients （18 males, 20 females）, with mean age of 13.4 years, were included in this study. As part of orthodontic treatment planning the patients were required to take dental Cone-beam CT （CBCT） covering the region of lower incisors, the sur- rounding alveolar bone and the mandibular symphysis. The cephalometric parameters were designed and measured to indicate the inclination of lower central incisor and physical morphology of the adjacent alveolar bone. Computer-aided descriptive statistical analysis was performed using SPSS 15.0 software package for Windows. A correlation analysis and a linear regression analysis between the incisor inclination and the alveolar bone morphology were performed. Results Significant positive correlations were found between the lower central incisor inclination and the morphological contour of the alveolar bone （P〈0.05）. The lower central incisor root apex was closer to the lingual alveolar crest when it was buccally inclined. Conclusion The morphology of the alveolar bone may be affected by incisal inclination.

Impacted Lower Third Molar Fused with a Supernumerary Tooth—Diagnosis and Treatment Planning Using Cone-Beam Computed Tomography

This paper reported a case of fusion between an impacted third molar and a supernumerary tooth, in which a surgical intervention was carried out, with the objective of removing the dental elements. The panoramic radiography was complemented by the Donovan＇s radiographic technique; but because of the proximity of the dental element to the mandibular ramus, it was not possible to have a final fusion diagnosis. Hence, the Cone-Beam Computed Tomography--which provides precise three- dimensional information--was used to determinate the fusion diagnosis and also to help in the surgical planning. In this case report we observed that the periapical, occlusal and panoramic were not able to show details which could only be examined through the cone-beam computed tomo- graphy.

Validation of a novel imaging approach using multi-slice CT and cone-beam CT to follow-up on condylar remodeling after bimaxillary surgery

The main goal of this study was to introduce a novel three-dimensional procedure to objectively quantify both inner and outer condylar remodelling on preoperative multi-slice computed tomography （MSCT） and postoperative cone-beam computed tomography （CBCT） images. Second, the reliability and accuracy of this condylar volume quantification method was assessed. The mandibles of 20 patients （11 female and 9 male） who underwent bimaxillary surgery were semi-automatically extracted from MSCT/CBCT scans and rendered in 3D. The resulting condyles were spatially matched by using an anatomical landmark-based registration procedure. A standardized sphere was created around each condyle, and the condylar bone volume within this selected region of interest was automatically calculated. To investigate the reproducibility of the method, inter- and intra-observer reliability was calculated for assessments made by two experienced radiologists twice five months apart in a set of ten randomly selected patients. To test the accuracy of the bone segmentation, the inner and outer bone structures of one dry mandible, scanned according to the clinical set-up, were compared with the gold standard, micro-CT. Thirty-eight condyles showed a significant （P〈O.05） mean bone volume decrease of 26.4%_ 11.4% （502.9 mm3＋ 268.1 mm3）. No significant effects of side, sex or age were found. Good to excellent （ICC〉 0.6） intra- and inter-observer reliability was observed for both MSCT and CBCT. Moreover, the bone segmentation accuracy was less than one voxel （0.4 mm） for MSCT （0.3 mm __. 0.2 mm） and CBCT （0.4 mm _ 0.3 mm）, thus indicating the clinical potential of this method for objective follow-up in pathological condylar resorption.

Slice-wise reconstruction for low-dose cone-beam CT using a deep residual convolutional neural network

Because of the growing concern over the radiation dose delivered to patients, X-ray cone-beam CT(CBCT) imaging of low dose is of great interest. It is difficult for traditional reconstruction methods such as Feldkamp to reduce noise and keep resolution at low doses. A typical method to solve this problem is using optimizationbased methods with careful modeling of physics and additional constraints. However, it is computationally expensive and very time-consuming to reach an optimal solution. Recently, some pioneering work applying deep neural networks had some success in characterizing and removing artifacts from a low-dose data set. In this study,we incorporate imaging physics for a cone-beam CT into a residual convolutional neural network and propose a new end-to-end deep learning-based method for slice-wise reconstruction. By transferring 3D projection to a 2D problem with a noise reduction property, we can not only obtain reconstructions of high image quality, but also lower the computational complexity. The proposed network is composed of three serially connected sub-networks: a cone-to-fan transformation sub-network, a 2D analytical inversion sub-network, and an image refinement sub-network. This provides a comprehensive solution for end-to-end reconstruction for CBCT. The advantages of our method are that the network can simplify a 3D reconstruction problem to a 2D slice-wise reconstruction problem and can complete reconstruction in an end-to-end manner with the system matrix integrated into the network design. Furthermore, reconstruction can be less computationally expensive and easily parallelizable compared with iterative reconstruction methods.

Improvements to conventional X-ray tube-based cone-beam computed tomography system

Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-ray tubes fulfill the requirements for industrial applications, because of their high tube voltage and power. Continuous improvements have been made to CX-CBCT systems, such as imaging time shortening,acquisition strategy optimization, and imaging software development, etc. In this study, a CX-CBCT system is developed. Additionally, some improvements to the CX-CBCT system are proposed based on the hardware conditions of the X-ray tube and detector. A near-detector(ND)geometry condition is employed to obtain a sharper image and larger detection area. An improved acquisition strategy is proposed to simplify operations and reduce total imaging time. In the ND geometry condition, a simplified method called FBP slice stacking(SS-FBP) is proposed, which can be applied to 3D image reconstruction. SS-FBP is timesaving relative to traditional methods. Furthermore, imaging software for the CX-CBCT system is developed in the MATLAB environment. Several imaging experiments were performed. The results suggest that the CX-CBCT system works properly, and that the above improvements are feasible and practical.

Scatter correction method for cone-beam CT based on interlacing-slit scan

Cone-beam computed tornography （CBCT） has the notable features of high efficiency and high precision, and is widely used in areas such as medical imaging and industrial non-destructive testing. However, the presence of the ray scatter reduces the quality of CT images. By referencing the slit collimation approach, a scatter correction method for CBCT based on the interlacing-slit scan is proposed. Firstly, according to the characteristics of CBCT imaging, a scatter suppression plate with interlacing slits is designed and fabricated. Then the imaging of the scatter suppression plate is analyzed, and a scatter correction Calculation method for CBCT based on the image fusion is proposed, which can splice out a complete set of scatter suppression projection images according to the interlacing-slit projection images of the left and the right imaging regions in the scatter suppression plate, and simultaneously complete the scatter correction within the fiat panel detector （FPD）. Finally, the overall process of scatter suppression and correction is provided. The experimental results show that this method can significantly improve the clarity of the slice images and achieve a good scatter correction.

Multiple helical scans and the reconstruction of over FOV-sized objects in cone-beam CT

In cone-beam computed tomography （CBCT）, there are often cases where the size of the specimen is larger than the field of view （FOV） （referred to as over FOV-sized （OFS））. To acquire the complete projection data for OFS objects, some scan modes have been developed for long objects and short but over-wide objects. However, these modes still cannot meet the requirements for both longitudinally long and transversely wide objects. In this paper, we propose a multiple helical scan mode and a corresponding reconstruction algorithm for both longitudinally long and transversely wide objects. The simulation results show that our model can deal with the problem and that the results are acceptable, while the OFS object is twice as long compared with the FOV in the same latitude.

Performance evaluation of the backprojection filtered (BPF) algorithm in circular fan-beam and cone-beam CT

In this article we introduce an exact backprojection filtered (BPF) type reconstruction algorithm for cone-beam scans based on Zou and Pan’s work. The algorithm can reconstruct images using only the projection data passing through the parallel PI-line segments in reduced scans. Computer simulations and practical experiments are carried out to evaluate this algorithm. The BPF algorithm has a higher computational efficiency than the famous FDK algorithm. The BPF algorithm is evaluated using the practical CT projection data on a 450 keV X-ray CT system with a flat-panel detector (FPD). From the practical experiments, we get the spatial resolution of this CT system. The algo- rithm could achieve the spatial resolution of 2.4 lp/mm and satisfies the practical applications in industrial CT inspec- tion.

Effects of Irregular Respiratory Motion on the Positioning Accuracy of Moving Target with Free Breathing Cone-Beam Computerized Tomography

For positioning a moving target, a maximum intensity projection (MIP) or average intensity projection (AIP) image derived from 4DCT is often used as the reference image which is matched to free breathing cone-beam CT (FBCBCT) before treatment. This method can be highly accurate if the respiratory motion of the patient is stable. However, a patient’s breathing pattern is often irregular. The purpose of this study is to investigate the effects of irregular respiration on positioning accuracy for a moving target aligned with FBCBCT. Nine patients’ respiratory motion curves were selected to drive a Quasar motion phantom with one embedded cubic and two spherical targets. A 4DCT of the phantom was acquired on a CT scanner (Philips Brilliance 16) equipped with a Varian RPM system. The phase binned 4DCT images and the corresponding MIP and AIP images were transferred into Eclipse for analysis. FBCBCTs of the phantom driven by the same respiratory curves were also acquired on a Varian TrueBeam and fused such that both CBCT and MIP/AIP images share the same target zero positions. The sphere and cube volumes and centroid differences (alignment error) determined by MIP, AIP and FBCBCT images were calculated, respectively. Compared to the volume determined by MIP, the volumes of the cube, large sphere, and small sphere in AIP and FBCBCT images were smaller. The alignment errors for the cube, large sphere and small sphere with center to center matches between MIP and FBCBCT were 2.5 ± 1.8 mm, 2.4 ± 2.1 mm, and 3.8 ± 2.8 mm, and the alignment errors between AIP and FBCBCT were 0.5 ± 1.1 mm, 0.3 ± 0.8 mm, and 1.8 ± 2.0 mm, respectively. AIP images appear to be superior reference images to MIP images. However, irregular respiratory pattern could compromise the positioning accuracy, especially for smaller targets.

Short-term outcomes of radiofrequency ablation for hepatocellular carcinoma using cone-beam computed tomography for planning and image guidance

BACKGROUND Percutaneous radiofrequency ablation(RFA)is an effective treatment for unresectable hepatocellular carcinoma(HCC)and a minimally invasive alternative to hepatectomy for treating tumour recurrence.RFA is often performed using contrast-enhanced computed tomography(CECT)and/or ultrasonography.In recent years,angiographic systems with flat panel image detectors and advanced image reconstruction algorithms have broadened the clinical applications of cone-beam computed tomography(CBCT),including RFA.Several studies have shown the effectiveness of using CBCT for immediate treatment assessments and follow-ups.AIM To assess the treatment response to RFA for HCC using CBCT.METHODS Forty-eight patients(44 men;aged 37-89 years)with solitary HCC[median size:3.2(1.2-6.6)cm]underwent RFA and were followed for 25.6(median;13.5-35.2)mo.Image fusion of CBCT and pre-operative CECT or magnetic resonance imaging(MRI)was used for tumour segmentation and needle path and ablation zone planning.Real-time image guidance was provided by overlaying the threedimensional image of the tumour and needle path on the fluoroscopy image.Treatment response was categorized as complete response(CR),partial response(PR),stable disease(SD),or progressive disease(PD).Disease progression,death,time to progression(TTP),and overall survival(OS)were recorded.Kaplan-Meier and Cox regression analyses were performed.RESULTS Initial post-RFA CECT/MRI showed 38 cases of CR(79.2%),10 of PR(20.8%),0 of SD,and 0 of PD,which strongly correlated with the planning estimation(42 CR,87.5%;6 PR,12.5%;0 SD;and 0 PD;accuracy:91.7%,P<0.01).Ten(20.8%)patients died,and disease progression occurred in 31(35.4%,median TTP:12.8 mo)patients,resulting in 12-,24-,and 35-mo OS rates of 100%,81.2%,and 72.2%,respectively,and progression-free survival(PFS)rates of 54.2%,37.1%,and 37.1%,respectively.The median dose-area product of the procedures was 79.05 Gy*cm2(range 40.95-146.24 Gy*cm2),and the median effective dose was 10.27 mSv(range 5.32-19.01 mSv).Tumour size<2 cm(P=0.008)was a significant factor for OS,while age(P=0.001),tumour size<2 cm(P<0.001),tumour stage(P=0.010),and initial treatment response(P=0.003)were significant factors for PFS.CONCLUSION Reliable RFA treatment planning and satisfactory outcomes can be achieved with CBCT.

Performance evaluation of the simpli¯ed spherical harmonics approximation for cone-beam X-ray luminescence computed tomography imaging

As an emerging molecular imaging modality,cone-beam X-ray luminescence computed tomog-raphy(CB-XLCT)uses X-ray-excitable probes to produce near-infrared(NIR)luminescence and then reconst ructs three-dimensional(3D)distribution of the probes from surface measurements.A proper photon-transportation model is critical to accuracy of XLCT.Here,we presented a systematic comparison between the common-used Monte Carlo model and simplified spherical harmonics(SPN).The performance of the two methods was evaluated over several main spec-trums using a known XLCT material.We designed both a global measurement based on the cosine similarity and a locally-averaged relative error,to quantitatively assess these methods.The results show that the SP_(3) could reach a good balance between the modeling accuracy and computational efficiency for all of the tested emission spectrums.Besides,the SP_(1)(which is equivalent to the difusion equation(DE))can be a reasonable alternative model for emission wavelength over 692nm.In vivo experiment further demonstrates the reconstruction perfor-mance of the SP:and DE.This study would provide a valuable guidance for modeling the photon-transportation in CB-XLCT.

An analytical simulation technique for cone-beam CT and pinhole SPECT

This study was aimed at developing an efficient simulation technique with an ordinary PC.The work involved derivation of mathematical operators,analytic phantom generations,and effective analytical projectors developing for cone-beam CT and pinhole SPECT imaging.The computer simulations based on the analytical projectors were developed by ray-tracing method for cone-beam CT and voxel-driven method for pinhole SPECT of degrading blurring.The 3D Shepp-Logan,Jaszczak and Defrise phantoms were used for simulation evaluations and image reconstructions.The reconstructed phantom images were of good accuracy with the phantoms.The results showed that the analytical simulation technique is an efficient tool for studying cone-beam CT and pinhole SPECT imaging.

Derivative-Hilbert-Backprojection based image reconstruction from truncated projections in helical cone-beam CT

In helical cone-beam computed tomography(CT), Feldkamp-Davis-Kress(FDK) based image reconstruction algorithms are by far the most popular. However, artifacts are commonly met in the presence of lateral projection truncation. The reason is that the ramp filter is global. To restrain the truncation artifacts, an approximate reconstruction formula is proposed based on the Derivative-Hilbert-Backprojection(DHB) framework. In the method, the first order derivative filter is followed by the Hilbert transform. Since the filtered projection values are almost zero by the first order derivative filter, the following Hilbert transform has little influence on the projection values, even though the projections are laterally truncated. The proposed method has two main advantages. First, it has comparable computational efficiency and image quality as well as the conventional helical FDK algorithm for non-truncated projections. The second advantage is that images can be reconstructed with acceptable quality and much lower computational cost in comparison to the Laplace operator based algorithm in cases with truncated projections. To point out the advantages of our method, simulations on the computer and real data experiments on our laboratory industrial cone-beam CT are conducted. The simulated and experimental results demonstrate that the method is feasible for image reconstruction in the case of projection truncation.

Usefulness of intra-procedural cone-beam computed tomography in modified balloon-occluded retrograde transvenous obliteration of gastric varices

AIM:To evaluate whether intra-procedural conebeam computed tomography(CBCT)performed during modified balloon-occluded retrograde transvenous obliteration(mB RTO)can accurately determine technical success of complete variceal obliteration.METHODS:From June 2012 to December 2014,15 patients who received CBCT during m BRTO for treatment of portal hypertensive gastric variceal bleeding were retrospectively evaluated.Three-dimensional(3D)CBCT images were performed and evaluated prior to the end of the procedure,and these were further analyzed and compared to the pre-procedure contrast-enhanced computed tomography to determine the technical success of m BRTO including:Complete occlusion/obliteration of:(1)gastrorenal shunt(GRS);(2)gastric varices;and(3)afferent feeding veins.Post-mB RTO contrast-enhanced CT was used to confirm the accuracy and diagnostic value of CBCT within 2-3 d.RESULTS:Intra-procedural 3D-CBCT images were 100% accurate in determining the technical success of m BRTO in all 15 cases.CBCT demonstrated complete occlusion/obliteration of GRS,gastric varices,collaterals and afferent feeding veins during m BRTO,which was confirmed with post-m BRTO CT.Two patients showed incomplete obliteration of gastric varices and feeding veins on CBCT,which therefore required additional gelfoam injections to complete the procedure.No patient required additional procedures or other interventions during their follow-up period(684 ± 279 d).CONCLUSION:CBCT during mB RTO appears to accurately and immediately determine the technical success of mB RTO.This may improve the technical and clinical success/outcome of m BRTO and reduce additional procedure time in the future.

Practical limitations of cone-beam computed tomography in 3D cephalometry

3D cone beam computed tomography(CBCT) images offer a unique and new appreciation of the anatomical structures and underlying anomalies not possible with conventional radiographs.However,in almost all aspects of CBCT imaging,from utilization to application,inherent limitations and pitfalls exist.Importantly,these inherent limitations and pitfalls have practical implications which need to be addressed before the potential of this technology can be fully realized.The purpose of this review was to explore the current limitations and pitfalls associated with CBCT imaging to allow for better and more accurate understanding of the possibilities this imaging modality could offer,particularly pertaining to 3D cephalometry.

Method for Converting Cone-Beam CT Values into Hounsfield Units for Radiation Treatment Planning

Cone-beam CT (CBCT) images acquired during radiation treatment can be used to recalculate the dose distribution as well as to confirm the treatment location. However, it is difficult to obtain the electron densities (EDs) necessary for dose calculation from CBCT images because of the effects of scatter contamination during CBCT image acquisition. This paper presents a mathematical method for converting the pixel values of CBCT images (CBCT values) into Hounsfield units (HUs) of radiation treatment simulation CT (simCT) images for use in radiation treatment planning. CBCT values are converted into HUs by matching the histograms of the CBCT values with the histograms of the HUs for each slice via linear scaling of the CBCT values. For prostate cancer and head-and-neck cancer patients, the EDs obtained from converted CBCT values (mCBCT values) show good agreement with the EDs obtained from HUs, within approximately 3.0%, and the dose calculated on the basis of CBCT images shows good agreement with the dose calculated on the basis of the simCT images, within approximately 2.0%. Because the CBCT values are converted for each slice, this conversion method can account for variation in the CBCT values associated with differences in body size, body shape, and inner tissue structures, as well as in longitudinally displaced positions from the isocenter, unlike conventional methods that use electron density phantoms. This method improves on conventional CBCT-ED conversion and shows considerable potential for improving the accuracy of radiation treatment planning using CBCT images.