Cone-beam Computed Tomography Image Sets Research Articles

A comparative study of rectal volume variation in patients with prostate cancer: A tertiary care center study

IntroductionEvery day variations in rectal filling in prostate cancer radiotherapy can significantly alter the delivered dose distribution from what was intended. The goal of this study was to see if the time of treatment delivery affected the rectal filling. MethodsThis is a retrospective study which included 50 patients with localized prostate cancer treated with volumetric modulated arc therapy (VMAT) to the primary and regional lymph nodes. Cone Beam Computed Tomography (CBCT) image-sets were done for all patient's daily setup verification. The radiation therapist contoured the rectum on all CBCT image sets. The rectal volumes delineated on CBCT and the planning CT image sets were compared. The change in rectal volumes between morning and afternoon treatments were calculated and compared. ResultsA total of 1000 CBCT image sets were obtained on 50 patients in the morning and afternoon. The percentage variation of the CBCT rectal volumes over the planning CT scan was 16.57% in the AM group and 24.35% in the PM group. ConclusionThe percentage change in rectal volume was significantly lesser in AM group compared to PM group and therefore morning treatments may result in dose distribution that is close to the intended dose distribution. Implications for practiceIn prostate cancer radiotherapy our study suggests that a simple technique of changing the time of treatment from afternoon to morning can help to reduce the rectal volume.

Age estimation based on 3D pulp segmentation of first molars from CBCT images using U-Net.

To train a U-Net model to segment the intact pulp cavity of first molars and establish a reliable mathematical model for age estimation. We trained a U-Net model by 20 sets of cone-beam CT images and this model was able to segment the intact pulp cavity of first molars. Utilizing this model, 239 maxillary first molars and 234 mandibular first molars from 142 males and 135 females aged 15-69 years old were segmented and the intact pulp cavity volumes were calculated, followed by logarithmic regression analysis to establish the mathematical model with age as the dependent variable and pulp cavity volume as the independent variable. Another 256 first molars were collected to estimate ages with the established model. Mean absolute error and root mean square error between the actual and the estimated ages were used to assess the precision and accuracy of the model. The dice similarity coefficient of the U-Net model was 95.6%. The established age estimation model was [Formula: see text] (V is the intact pulp cavity volume of the first molars). The coefficient of determination (R2), mean absolute error and root mean square error were 0.662, 6.72 years, and 8.26 years, respectively. The trained U-Net model can accurately segment pulp cavity of the first molars from three-dimensional cone-beam CT images. The segmented pulp cavity volumes could be used to estimate the human ages with reasonable precision and accuracy.

Evaluation of Dose Calculation Based on Cone-Beam CT Using Different Measuring Correction Methods for Head and Neck Cancer Patients.

Purpose: To investigate and compare 2 cone-beam computed tomography (CBCT) correction methods for CBCT-based dose calculation. Materials and Methods: Routine CBCT image sets of 12 head and neck cancer patients who received volumetric modulated arc therapy (VMAT) treatment were retrospectively analyzed. The CBCT images obtained using an on-board imager (OBI) at the first treatment fraction were firstly deformable registered and padded with the kVCT images to provide enough anatomical information about the tissues for dose calculation. Then, 2 CBCT correction methods were developed and applied to correct CBCT Hounsfield unit (HU) values. One method (HD method) is based on protocol-specific CBCT HU to physical density (HD) curve, and the other method (HM method) is based on histogram matching (HM) of HU value. The corrected CBCT images (CBCTHD and CBCTHM for HD and HM methods) were imported into the original planning system for dose calculation based on the HD curve of kVCT (the planning CT). The dose computation result was analyzed and discussed to compare these 2 CBCT-correction methods. Results: Dosimetric parameters, such as the Dmean, Dmax and D5% of the target volume in CBCT plan doses, were higher than those in the kVCT plan doses; however, the deviations were less than 2%. The D2%, in parallel organs such as the parotid glands, the deviations from the CBCTHM plan dose were less than those of the CBCTHD plan dose. The differences were statistically significant (P < .05). Meanwhile, the V30 value based on the HM method was better than that based on the HD method in the oral cavity region (P = .016). In addition, we also compared the γ passing rates of kVCT plan doses with the 2 CBCT plan doses, and negligible differences were found. Conclusion: The HM method was more suitable for head and neck cancer patients than the HD one. Furthermore, with the CBCTHM-based method, the dose calculation result better matches the kVCT-based dose calculation.

Planning Margins Determined by Inter Fractional Errors for Patients with Hepatocarcinoma—A Real-World Practice

<h3>Purpose/Objective(s)</h3> With the progress of radiation techniques, radiotherapy is increasingly widely used in the treatment of hepatocarcinoma. Previous studies showed high radio-sensitivity and frequently motion of hepatobiliary zone. Although the application of magnetic resonance simulation (MR) and four-dimensional computed tomography (4D-CT) help us to clearly the gross tumor volume (GTV), accurate calculation of set-up margin is required to define the clinical to planning target volume margin. This study aimed at calculate the suitable margin between clinical target volume (CTV) and planning target volume (PTV) after the evaluation of the set-up errors using cone beam computed tomography (CBCT). <h3>Materials/Methods</h3> Patients aged 18-85 years old with pathologically diagnosed as primary hepatocarcinoma, Eastern Cooperative Oncology Group performance score ≤ 3 points, accepted the radiation recommendation by multi-disciplinary team, with only one tumor located in liver will be enrolled. Both 4D-CT and MR simulations were delivered to determine GTV. CTV was GTV plus a 5 mm margin in liver and GTV plus a 10mm margin along vessels if tumor embolus were included. PTV was CTV plus a 5mm margin. All the patients received image guided intensity modulated radiotherapy with conventional fractionation. CBCT was prescribed daily at the first week and then 2-3 times at every following week. Patients whose tumor could not be clearly classified in CBCT will be excluded. CBCT The setup errors in translational directions were recorded based on the image registration between the CBCT and the free breath CT images at simulation as reference images. Mean value and standard deviations (∑) of each patient were obtained. After that, we calculated the margin between CTV and PTV by a formula MPTV=2.5∑+0.7σ (σ means rootmeansquare of ∑). <h3>Results</h3> From November 2020 to April 2021, 35 patients fulfilled the criteria. The median age of these patients were 65 years old. The median value of GTV and PTV were 512.91 ml (45.09-1987.56 ml) and 1074.77ml (221.09-3028.40 ml), respectively. The median body mass index (BMI)was 23.98. The median CBCT times was 8 (5-12). After alignments by one senior radiation oncologist and one senior radiation therapist, we analyzed 284 sets of CBCT images. M±SD shifts in translational were 0.04±0.25 mm (LR), 0.05±0.51 mm (AP), and 0.06±0.26 mm (SI), respectively. Accordingly, the margins in LR, SI and AP directions were 5 mm, 6 mm and 10 mm, respectively. For patients whose BMI <24, the margins in LR, SI and AP directions were 4 mm, 5 mm and 12 mm. For patients whose BMI ≥24, the corresponding margins should be 6 mm,7 mm and 10 mm, respectively. <h3>Conclusion</h3> For patients with hepatocarcinoma, the setup errors were different in LR, SI and AP directions. We recommended that the margins from CTV to PTV should be 5mm, 6mm and 10 mm in LR, SI and AP directions. For patients with BMI≥24, larger margins in LR and SI directions are needed.

The Learning Curve of Artificial Intelligence for Dental Implant Treatment Planning: A Descriptive Study

Introduction: Cone-beam computed tomography (CBCT) has been applied to implant dentistry. The increasing use of this technology produces a critical number of images that can be used for training artificial intelligence (AI). Objectives: To investigate the learning curve of the developed AI for dental implant planning in the posterior maxillary region. Methods: A total of 184 CBCT image sets of patients receiving posterior maxillary implants were processed with software (DentiPlan Pro version 3.7; NECTEC, NSTDA, Thailand) to acquire 316 implant position images. The planning software image interfaces were anonymously captured with full-screen resolution. Three hundred images were randomly sorted to create six data sets, including 1–50, 1–100, 1–150, 1–200, 1–250, and 1–300. The data sets were used to develop AI for dental implant planning through the IBM PowerAI Vision platform (IBM Thailand Co., Ltd., Bangkok, Thailand) by using a faster R-CNN algorithm. Four data augmentation algorithms, including blur, sharpen, color, and noise, were also integrated to observe the improvement of the model. After the testing process with 16 images that were not included in the training set, the recorded data were analyzed for detection and accuracy to generate the learning curve of the model. Results: The learning curve revealed some similar patterns. The curve trend of the original and blurred augmented models was in a similar pattern in the panoramic image. In the last training set, the blurred augmented model improved the detection by 12.50%, but showed less accuracy than the original model by 18.34%, whereas the other three augmented models had different patterns. They were continuously increasing in both detection and accuracy. However, their detection dropped in the last training set. The colored augmented model demonstrated the best improvement with 40% for the panoramic image and 18.59% for the cross-sectional image. Conclusions: Within the limitation of the study, it may be concluded that the number of images used in AI development is positively related to the AI interpretation. The data augmentation techniques to improve the ability of AI are still questionable.

Comparison of Cone Beam Computed Tomography and Digital Radiography in Detecting Separated Endodontic Files and Strip Perforation

The separation of endodontic files and strip perforation are among procedural intraoperative complications which may ultimately lead to the failure of root canal treatment. The aim of the present study was to compare the diagnostic potential of cone beam computed tomography (CBCT) and digital periapical radiographs in detecting separated rotary files and strip perforation in filled canals. Fifty human mandibular molars were selected for this study. The teeth were randomly divided into two groups based on endodontic errors (i.e., file separation and strip perforation). In each group, 25 of 50 mesial canals were randomly chosen for simulating the errors, while the other 25 canals were considered as the control group. In group one, a simulation of the separation of rotary files was performed using ProTaper F2 files. Strip perforation of the root canals in group two was achieved by number 2 and 3 Gates Glidden drills in the coronal third of the root canals. Digital periapical radiographs in two different horizontal angles and high-resolution CBCT scans were obtained from the teeth mounted on a dry human mandible with simulated soft tissue covering. Three experienced observers who were unaware of the study groups evaluated the digital periapical and CBCT image sets in two separate readings. Intraobserver and interobserver agreements, as well as accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), were calculated and compared. Intraobserver and interobserver agreements ranged from poor to excellent and poor to good, respectively. The accuracy, sensitivity, specificity, PPV, and NPV for digital radiography in detecting separated files were 0.950, 0.813, 0.957, 0.929, and 0.880, respectively. The same values for CBCT were 0.747, 0.667, 0.900, 0.833, and 0.783, respectively. For the diagnosis of strip perforation, these values were 0.855, 0.800, 0.909, 0.889, and 0.833 for periapical radiography and 0.955, 1.000, 0.920, 0.926, and 1.000 for CBCT. In conclusion, CBCT was superior for diagnosing strip perforation of the filled root canals, while digital periapical radiographs performed better in the detection of separated rotary files.

Comparison of radiographical characteristics and diagnostic accuracy of intraosseous jaw lesions on panoramic radiographs and CBCT.

To investigate the differences in imaging characteristics and the diagnostic accuracy of 225 intraosseous jaw lesions on panoramic radiographs (PAN) versus cone beam computed tomography (CBCT). 225 sets of PAN and CBCT images with biopsy-proven histopathological diagnoses were retrospectively compared in terms of radiographic features and diagnostic accuracy. The imaging characteristics of PAN and CBCT were independently evaluated by two oral and maxillofacial radiologists who were required to answer 12 questions and provided up to three differential diagnoses with their confidence scores. Odds ratios (ORs) were statistically significant for border cortication (OR = 1.521; p = .003) and border continuity (OR = 0.421; p = .001), involvement on neurovascular canals (OR = 2.424; p < .001), expansion (OR = 7.948; p < .001), cortical thinning (OR = 20.480; p < .001) as well as its destruction (OR = 25.022; p < .001) and root resorption (OR = 2.477; p < .001). Furthermore, imaging features in the posterior and mandibular regions showed better agreement than those in the anterior and maxillary regions, respectively. The diagnostic accuracy of the first differential diagnosis was higher on CBCT than on PAN (Observer 1:78.7 vs 64.4%; Observer 2: 78.7 vs 70.2% (p < .001)). The observers' confidence scores were also higher at CBCT interpretation compared with PAN. CBCT demonstrated a greater number of imaging characteristics of intraosseous jaw lesions compared with PAN, especially in the anterior regions of both jaws and in the maxilla. Diagnostic accuracy is improved with CBCT compared to PAN, especially for lesions in the maxilla. Radiologists have greater confidence when using CBCT.

Quantitative Comparison of Cephalogram and Cone-Beam Computed Tomography in the Evaluation of Alveolar Bone Thickness of Maxillary Incisors.

This study aims to quantitatively compare cephalogram and cone-beam computed tomography (CBCT) when evaluating maxillary central incisor alveolar bone thickness. We used 30 sets of lateral cephalograms and CBCT images that were recorded at the same time. Labial, buccal, and overall alveolar bone thicknesses were measured on three measurement lines of the forward-most incisor in lateral cephalograms and four maxillary incisors in CBCT images. Paired t-test, interclass correlation coefficient analysis, one-way analysis of variance (ANOVA), and Bland-Altman analysis were used to assess cephalometrically measured alveolar bone thickness of maxillary incisors and compare these measurements with those made using CBCT images. Significant differences were observed between cephalometric and CBCT-based measurements of maxillary incisor alveolar bone thickness; most values showed mild or moderate correlation between the two methods. In most cases, cephalometric measurements were greater than CBCT-based measurements. Bland-Altman plots and ANOVA revealed that measurement bias increased when measurement lines moved apically. Alveolar bone thickness was always overestimated on cephalograms. Maxillary incisor alveolar bone thickness is always overestimated on cephalograms compared with CBCT-based measurements, with the overestimations ranging from 0.3 to 1.3 mm. Cephalometric measurement bias increases when measurement lines move apically. Thus, CBCT should be recommended when the accurate evaluation of alveolar bone thickness is warranted.

A technical note on intra-arterial cone-beam computed tomography for the evaluation of flow-diverter stents: Image quality differences between diluted and non-diluted contrast medium.

Design of flow-diverter stents for flexibility, tractability, and low profile limits their radiopacity on conventional digital subtraction angiography. Cone-beam computed tomography (CBCT) offers higher spatial resolution for the evaluation of flow-diverter stents. However, CBCT requires optimal dilution and timing of contrast medium for simultaneous visualization of the stent, arterial lumen, and vessel wall. There are only limited data on the effects of different contrast dilutions on CBCT image quality in neurointerventional applications. In our institution, intra-arterial CBCTs were acquired during stent deployment and at follow-ups with 10% diluted contrast. We had recently started acquiring intra-arterial CBCTs with non-diluted contrast. Retrospective analysis of our flow-diverter data identified eight cases with different aneurysm locations who had intra-arterial CBCT with 10% diluted contrast immediately after flow-diverter stent deployment and with non-diluted contrast technique during follow-ups. For each case, the image quality between diluted and non-diluted contrast techniques was compared qualitatively by assessing stent visualization and quantitatively by plotting gray-scale intensity values along the vessel lumen. In two sets of CBCT images per each case, there was no substantial difference between diluted and non-diluted CBTC techniques for the evaluation of stent architecture and lumen opacification. Gray-scale intensity values perpendicular to the lumen revealed similar intensity values along the neighboring parenchyma, vessel wall, and lumen for the two different contrast techniques. Intra-arterial CBCT angiography can be performed without contrast dilution and still achieve adequate image quality in certain cerebral aneurysms treated with flow diverter. The non-diluted contrast technique avoids the time loss during preparation of diluted contrast and installation of diluted contrast to the injector in angiography suites with a single power injector.

Deep Inspiration Breath Hold Provides Fewer Set-up Errors Compared with Free Breathing for Whole-Breast Radiation

To compare the set-up errors between deep inspiration breath-hold (DIBH) and free breathing (FB) for breast cancer patients who were treated with whole breast irradiation (WBI). We retrospectively enrolled 30 breast cancer patients receiving breast conserving surgery (BCS) following WBI using DIBH treated in our institution from April 2016 to June 2018 as study cohort. For the comparator, we identified 30 patients receiving WBI with FB. The kilovoltage cone-beam computed tomography (CBCT) was performed to evaluate and reduce set-up errors. The differences of set-up errors between techniques were compared using an independent two-sample t-test. The optimal margins from clinical target volume (CTV) to planning target volume (PTV) for DIBH were estimated. A total of 318 sets of CBCT images were acquired, with an average of 5.1±1.1sets per patient. The set-up errors along the three translational directions (lateral, longitudinal, vertical) were 2.1±1.6 mm, 2.6±1.7 mm, 2.5±2.1 mm for DIBH, and 2.2±1.7mm，3.1±2.5mm，3.3±2.3mm for FB group, respectively. Compared with FB, DIBH significantly reduced set-up errors in longitudinal (p=0.015) and vertical (p=0.004) directions. The optimal margins from CTV to PTV using DIBH were 6.2 mm, 7.3mm and 7.8 mm, respectively. In DIBH group, first week’s treatments and high body mass index (BMI) did not associate with larger set-up deviation. DIBH technique provides less set-up errors than free breathing for breast cancer patients treated with whole breast irradiation. The CTV- PTV margins of 6-8mm are recommended for DIBH.

Study of setup error in cone beam CT for whole breast intensity-modulated radiotherapy with breast board immobilization

Objective To investigate the setup errors and influencing factors of the whole breast intensity-modulated radiotherapy (IMRT) after breast-conserving surgery, and to identify the margins from clinical target volume (CTV) to planning target volume (PTV). Methods Thirty patients with left-sided (n=15) or right-sided breast cancer (n=15) receiving whole breast hypofractionated IMRT with breast board immobilization after breast-conserving surgery in Cancer Hospital from 2016 to 2017 were enrolled. The kilo-voltage cone-beam computed tomography (CBCT) was used to compare the errors of planning CT and treatment unit and determine the setup errors. The margins from CTV to PTV were calculated. The setup errors under different conditions were statistically compared by t-test. Results A total of 151 sets of CBCT images were taken in the whole cohort, (5.0±1.3) sets per patient on average. The setup errors in the x-axis (left-right direction), y-axis (cranial-caudal direction) and z-axis (anterior-posterior direction) were (2.2±1.7) mm, (3.1±2.5) mm and (3.3±2.3) mm, respectively. The margins from CTV to PTV were 6.39 mm, 10.00 mm and 8.57 mm, respectively. The setup error in anterior-posterior direction in the first week was (3.7±2.5) mm, significantly larger than (2.6±1.6) mm in the following week (P=0.002). The setup error of the patients with overweight or obesity was (3.9±2.6) mm, significantly higher than (2.9±2.0) mm in those with normal weight in the z-axis direction (P=0.033). Conclusion The margins from CTV to PTV are recommended to be ranged from 6 to 10 mm during hypofractionated whole breast IMRT with breast board immobilization after breast-conserving surgery. More frequent imaging verification should be applied in the first week of IMRT. Key words: Breast neoplasm/radiotherapy; Cone-beam CT; Setup error; Margin

The radioanatomical assessment of the K\xf6rner\u2019s septum

Purpose of the studyKörner’s septum (KS) is a developmental remnant formed at the junction of mastoid and temporal squama, representing the persistence of the petrosquamosal suture. During mastoid surgery, it could be taken as a false medial wall of the antrum so that the deeper cells might not be explored. The aim of the study was to assess a Körner’s septum prevalence and to analyze its topography.MethodsThe study was performed on 80 sets of cone-beam computed tomography (CBCT) images of temporal bone (41 male, 39 female, 160 temporal bones). Körner’s septum was identified and its thickness was measured on axial sections at three points: at the level of superior semicircular canal (SCC), at the level of head of malleus (HM) and at the level of tympanic sinus (TS).ResultsKS was encountered at least in one point of measurements in 50 out of 80 sets of CBCT images (62.5%). The average thickness at the level of SCC was 0.87 ± 0.34 mm, at the level of HM was 0.99 ± 0.37 mm and at the level of TS was 0.52 ± 0.17 mm.ConclusionsKörner’s septum is a common structure in the temporal bone–air cell complex. It is more often encountered in men. In half of the patients, it occurs bilaterally. However, in most of the cases it is incomplete with anterior and superior portions being the most constant.

Interfractional diaphragm changes during breath-holding in stereotactic body radiotherapy for liver cancer.

IGRT based on bone matching may produce a large target positioning error in terms of the reproducibility of expiration breath-holding on SBRT for liver cancer. We evaluated the intrafractional and interfractional errors using the diaphragm position at the end of expiration by utilising Abches and analysed the factor of the interfractional error. Intrafractional and interfractional errors were measured using a couple of frontal kV images, planning computed tomography (pCT) and daily cone-beam computed tomography (CBCT). Moreover, max-min diaphragm position within daily CBCT image sets with respect to pCT and the maximum value of diaphragm position difference between CBCT and pCT were calculated. The mean±SD (standard deviation) of the intra-fraction diaphragm position variation in the frontal kV images was 1.0±0.7mm in the C-C direction. The inter-fractional diaphragm changes were 0.4±4.6mm in the C-C direction, 1.4±2.2mm in the A-P direction, and -0.6±1.8mm in the L-R direction. There were no significant differences between the maximum value of the max-min diaphragm position within daily CBCT image sets with respect to pCT and the maximum value of diaphragm position difference between CBCT and pCT. Residual intrafractional variability of diaphragm position is minimal, but large interfractional diaphragm changes were observed. There was a small effect in the patient condition difference between pCT and CBCT. The impact of the difference in daily breath-holds on the interfractional diaphragm position was large or the difference in daily breath-holding heavily influenced the interfractional diaphragm change.

Study to Compare the Effect of Different Registration Methods on Patient Setup Uncertainties in Cone-beam Computed Tomography during Volumetric Modulated Arc Therapy for Breast Cancer Patients.

Purpose:This study compared three different methods used in registering cone-beam computed tomography (CBCT) image set with planning CT image set for determining patient setup uncertainties during volumetric modulated arc therapy (VMAT) for breast cancer patients.Materials and Methods:Seven breast cancer patients treated with 50 Gy in 25 fractions using VMAT technique were chosen for this study. A total of 105 CBCT scans were acquired by image guidance protocol for patient setup verification. Approved plans’ CT images were used as the reference image sets for registration with their corresponding CBCT image sets. Setup errors in mediolateral, craniocaudal, and anteroposterior direction were determined using gray-scale matching between the reference CT images and onboard CBCT images. Patient setup verification was performed using clip-box registration (CBR) method during online imaging. Considering the CBR method as the reference, two more registrations were performed using mask registration (MR) method and dual registration (DR) (CBR + MR) method in the offline mode. For comparison, systematic error (∑), random error (σ), mean displacement vector (R), mean setup error (M), and registration time (Rt) were analyzed. Post hoc Tukey's honest significant difference test was performed for multiple comparisons.Results:Systematic and random errors were less in CBR as compared to MR and DR (P > 0.05). The mean displacement error and mean setup errors were less in CBR as compared to MR and DR (P > 0.05). Increased Rt was observed in DR as compared to CBR and MR (P < 0.05). In addition, multiple comparisons did not show any significant difference in patient setup error (P > 0.05).Conclusion:For breast VMAT plan delivery, all three registration methods show insignificant variation in patient setup error. One can use any of the three registration methods for patient setup verification.

43. CBCT dose calculation: accuracy assessment of four different methods

Introduction Cone Beam CT (CBCT) images aim at target volume repositioning before treatment fraction. These images may be used for dose calculation in order to dosimetrically quantify anatomical variations that occurs during treatment. The main limits are image quality, Hounsfield numbers (HU) consistency and CBCT reconstruction size. This study aims to assess accuracy of several CBCT dose calculation methods. Methods This study deals with four CBCT (XVI, Elekta) and CT image sets acquired on the same day in context of weekly dose planning of one H&N patient treated with VMAT technique. CT-CBCT sets were used to quantify CBCT dose calculation accuracy by investigating four methods: (i) use of a density to HU relation from phantom CBCT image (phantom HU-D relation), (ii) use of a density to HU relation from patient CBCT image (patient HU-D relation), (iii) density override by three classes threshold (air, soft tissues, bone) and (iv) elastic deformation (Admire, Elekta) between planning CT and CBCT image, by creating a pseudo-CT. After rigid registration, plan characteristics are projected on CBCT images (or pseudo-CT) with Pinnacle v.9.10 (Philips). Dose distribution comparison between CT-based (reference) and CBCT-based calculation was performed by a gamma analysis in 2D and 3D ( γ 2D and γ 3D, criteria: 2%/2 mm, 30% threshold). Then, dose differences were reported in terms of 95% target coverage, parotid glands mean dose (Dmean) and PRV spinal cord maximum dose (D2%). Results On average, γ 3D (percentage of points with gamma The gamma analysis showed location of discrepancy areas: near body contour, regarding shoulders and in presence of heterogeneities ( Fig. 1 ). These differences can be explained by the poor image quality and the HU inconsistency of CBCT images in some areas. The method with pseudo-CT seems to be the best to pass over these issues because densities come from planning CT. Conclusions The four evaluated methods show that dose differences can reach 5% for parotid glands and are lower than 2% for spinal cord and target volumes. The 3D gamma analysis results (2%/2 mm) are higher than 95% for three among four methods. However, additional uncertainties have to be taken into consideration in case of CBCT image delineation and/or calculation on truncated images. This preliminary study shows CBCT dose calculation feasibility to quantify impact of patient anatomical variations during treatment and trigger a new plan based on CT if necessary. The future work is real delivered dose monitoring, based on CBCT image, in perspective of dose guided adaptive radiotherapy.

Evaluation of Deformable Image Registration-Based Contour Propagation From Planning CT to Cone-Beam CT.

Purpose:We evaluated the performance of organ contour propagation from a planning computed tomography to cone-beam computed tomography with deformable image registration by comparing contours to manual contouring.Materials and Methods:Sixteen patients were retrospectively identified based on showing considerable physical change throughout the course of treatment. Multiple organs in the 3 regions (head and neck, prostate, and pancreas) were evaluated. A cone-beam computed tomography from the end of treatment was registered to the planning computed tomography using rigid registration, followed by deformable image registration. The contours were copied on cone-beam computed tomography image sets using rigid registration and modified by 2 radiation oncologists. Contours were compared using Dice similarity coefficient, mean surface distance, and Hausdorff distance.Results:The mean physician-to-physician Dice similarity coefficient for all organs was 0.90. When compared to each physician’s contours, the overall mean for rigid was 0.76 (P < .001), and it was improved to 0.79 (P < .001) for deformable image registration. Comparing deformable image registration to physicians resulted in a mean Dice similarity coefficient of 0.77, 0.74, and 0.84 for head and neck, prostate, and pancreas groups, respectively; whereas, the physician-to-physician mean agreement for these sites was 0.87, 0.90, and 0.93 (P < .001, for all sites). The mean surface distance for physician-to-physician contours was 1.01 mm, compared to 2.58 mm for rigid-to-physician contours and 2.24 mm for deformable image registration-to-physician contours. The mean physician-to-physician Hausdorff distance was 11.32 mm, and when compared to any physician’s contours, the mean for rigid and deformable image registration was 12.1 mm and 12.0 mm (P < .001), respectively.Conclusion:The physicians had a high level of agreement via the 3 metrics; however, deformable image registration fell short of this level of agreement. The automatic workflows using deformable image registration to deform contours to cone-beam computed tomography to evaluate the changes during treatment should be used with caution.

Biologically Optimized Online Patient Positioning for Prostate External Beam Radiation Therapy

The standard approach for target localization in prostate radiation therapy is to perform rigid registration between pretreatment cone beam CT (CBCT) and planning CT (PCT); however, due to internal organ deformation, online registration could be operator-dependent and suboptimal. We proposed a novel method to evaluate the delivered dose to target and organs-at-risk (OAR) over a range of potential treatment positions. Using this approach, we determined optimal positioning based on proper target dose coverage with minimal risk of complication to OAR. A set of 10 patients with low or intermediate-risk prostate cancer was evaluated retrospectively in this IRB-approved study. For each patient, a VMAT plan with one 358oarc was developed on the PCT to deliver 78 Gy in 39 fractions. The margin for planning target volume was 7 mm around prostate, except for 5 mm in the posterior direction. Five representative CBCT image sets were selected for each patient. The CBCT was registered to planning CT online by radiation therapists, who performed automatic match and manually adjusted for best agreement at the rectal and prostate interface. Consensus contours of prostate, bladder, and rectum were created on each CBCT by combining independent delineations from 5 oncologists, which represented the ground truth for these structures. For each CBCT, search for optimal treatment position was performed within a 7 mm radius from the online operator-matched position following two criteria. The first criterion required minimization of NTCPrectum for less NTCPbladder relative to the online matched position. The second criterion required maximization of the complication free probability [CFP: (1- NTCPrectum)×(1- NTCPbladder)]. Both criteria required better prostate Dmin and equivalent uniform dose (EUD, a = -4) than values from online matched position. NTCPrectum was calculated with the Lyman-Kutcher-Burman (LKB) model (n = 0.09, m = 0.13, TD50 = 76.9 Gy) (Michalski et al), and similarly the bladder (n = 0.00995, m = 0.022, TD50 = 77.6 Gy) (Cheung et al). The optimal treatment positons that fulfilled the first criterion were at 2 ± 3, 2 ± 2, 0 ± 2 mm (mean ± SD) right, anterior, and inferior to the online matched position, and demonstrated a reduction of 26.3 ± 23.9% in NTCPrectum (range, 0–84.7%), while attaining an average increase of prostate Dmin by 1.2 Gy (range, 0–11.8 Gy) and EUD by 0.3 Gy (range, 0–8.1 Gy) relative to those from the online matched positions. The second criterion provided an increase in CFP by 19.4 ± 18.1% (range, 0–59.8%) and an average increase of prostate Dmin by 2.8 Gy (range, 0–32.2 Gy), and EUD by 1.2 Gy (range, 0–38.5 Gy). The optimal positions were 1 ± 4, 1 ± 2, 2 ± 3 mm right, anterior, and inferior to the online matched position. These encouraging results suggest a role for optimization of patient positioning based on radiobiological optimization in the routine IGRT of prostate patients.

Automated planning of breast radiotherapy using cone beam CT imaging.

Develop and clinically validate a methodology for using cone beam computed tomography (CBCT) imaging in an automated treatment planning framework for breast IMRT. A technique for intensity correction of CBCT images was developed and evaluated. The technique is based on histogram matching of CBCT image sets, using information from "similar" planning CT image sets from a database of paired CBCT and CT image sets (n = 38). Automated treatment plans were generated for a testing subset (n = 15) on the planning CT and the corrected CBCT. The plans generated on the corrected CBCT were compared to the CT-based plans in terms of beam parameters, dosimetric indices, and dose distributions. The corrected CBCT images showed considerable similarity to their corresponding planning CTs (average mutual information 1.0±0.1, average sum of absolute differences 185 ± 38). The automated CBCT-based plans were clinically acceptable, as well as equivalent to the CT-based plans with average gantry angle difference of 0.99°±1.1°, target volume overlap index (Dice) of 0.89±0.04 although with slightly higher maximum target doses (4482±90 vs 4560±84, P < 0.05). Gamma index analysis (3%, 3 mm) showed that the CBCT-based plans had the same dose distribution as plans calculated with the same beams on the registered planning CTs (average gamma index 0.12±0.04, gamma <1 in 99.4%±0.3%). The proposed method demonstrates the potential for a clinically feasible and efficient online adaptive breast IMRT planning method based on CBCT imaging, integrating automation.

SU-E-J-214: Comparative Assessment On IGRT On Partial Bladder Cancer Treatment Between CT-On-Rails (CTOR) and KV Cone Beam CT (CBCT)

Purpose: Image-Guided radiation therapy(IGRT) depends on reliable online patient-specific anatomy information to address random and progressive anatomy changes. Large margins have been suggested to bladder cancer treatment due to large daily bladder anatomy variation. KV Cone beam CT(CBCT) has been used in IGRT localization prevalently; however, its lack of soft tissue contrast makes clinicians hesitate to perform daily soft tissue alignment with CBCT for partial bladder cancer treatment. This study compares the localization uncertainties of bladder cancer IGRT using CTon- Rails(CTOR) and CBCT. Methods: Three T2N0M0 bladder cancer patients (total of 66 Gy to partial bladder alone) were localized daily with either CTOR or CBCT for their entire treatment course. A total of 71 sets of CTOR and 22 sets of CBCT images were acquired and registered with original planning CT scans by radiation therapists and approved by radiation oncologists for the daily treatment. CTOR scanning entailed 2mm slice thickness, 0.98mm axial voxel size, 120kVp and 240mAs. CBCT used a half fan pelvis protocol from Varian OBI system with 2mm slice thickness, 0.98axial voxel size, 125kVp, and 680mAs. Daily localization distribution was compared. Accuracy of CTOR and CBCT on partial bladder alignment was also evaluated by comparing bladder PTV coverage. Results: 1cm all around PTV margins were used in every patient except target superior limit margin to 0mm due to bowel constraint. Daily shifts on CTOR averaged to 0.48, 0.24, 0.19 mms(SI,Lat,AP directions); CBCT averaged to 0.43, 0.09, 0.19 mms(SI,Lat,AP directions). The CTOR daily localization showed superior results of V100% of PTV(102% CTOR vs. 89% CBCT) and bowel(Dmax 69.5Gy vs. 78Gy CBCT). CTOR images showed much higher contrast on bladder PTV alignment. Conclusion: CTOR daily localization for IGRT is more dosimetrically beneficial for partial bladder cancer treatment than kV CBCT localization and provided better soft tissue PTV identification.

SU‐E‐J‐167: Improvement of Time‐Ordered Four Dimensional Cone‐Beam CT; Image Mosaicing with Real and Virtual Projections

Purpose:In the previous study, we developed time‐ordered fourdimensional (4D) cone‐beam CT (CBCT) technique to visualize nonperiodic organ motion, such as peristaltic motion of gastrointestinal organs and adjacent area, using half‐scan reconstruction method. One important obstacle was that truncation of projection was caused by asymmetric location of flat‐panel detector (FPD) in order to cover whole abdomen or pelvis in one rotation. In this study, we propose image mosaicing to extend projection data to make possible to reconstruct full field‐of‐view (FOV) image using half‐scan reconstruction.Methods:The projections of prostate cancer patients were acquired using the X‐ray Volume Imaging system (XVI, version 4.5) on Synergy linear accelerator system (Elekta, UK). The XVI system has three options of FOV, S, M and L, and M FOV was chosen for pelvic CBCT acquisition, with a FPD panel 11.5 cm offset. The method to produce extended projections consists of three main steps: First, normal three‐dimensional (3D) reconstruction which contains whole pelvis was implemented using real projections. Second, virtual projections were produced by reprojection process of the reconstructed 3D image. Third, real and virtual projections in each angle were combined into one extended mosaic projection. Then, 4D CBCT images were reconstructed using our inhouse reconstruction software based on Feldkamp, Davis and Kress algorithm. The angular range of each reconstruction phase in the 4D reconstruction was 180 degrees, and the range moved as time progressed.Results:Projection data were successfully extended without discontinuous boundary between real and virtual projections. Using mosaic projections, 4D CBCT image sets were reconstructed without artifacts caused by the truncation, and thus, whole pelvis was clearly visible.Conclusion:The present method provides extended projections which contain whole pelvis. The presented reconstruction method also enables time‐ordered 4D CBCT reconstruction of organs with non‐periodic motion with full FOV without projection‐truncation artifacts.This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003). This work was partly supported by JSPS KAKENHI 24234567.