Cone-beam Computed Tomography Image Acquisition Research Articles

A carbon nanotube x-ray source array designed for a new multisource cone beam computed tomography scanner

Cone beam computed tomography (CBCT) is known to suffer from strong scatter and cone beam artifacts. The purpose of this study is to develop and characterize a rapidly scanning carbon nanotube (CNT) field emission x-ray source array to enable a multisource CBCT (ms-CBCT) image acquisition scheme which has been demonstrated to overcome these limitations. A CNT x-ray source array with eight evenly spaced focal spots was designed and fabricated for a medium field of view ms-CBCT for maxillofacial imaging. An external multisource collimator was used to confine the radiation from each focal spot to a narrow cone angle. For ms-CBCT imaging, the array was placed in the axial direction and rapidly scanned while rotating continuously around the object with a flat panel detector. The x-ray beam profile, temporal and spatial resolutions, energy and dose rate were characterized and evaluated for maxillofacial imaging. The CNT x-ray source array achieved a consistent focal spot size of 1.10 ± 0.04 mm × 0.84 ± 0.03 mm and individual beam cone angle of 2.4° ± 0.08 after collimation. The x-ray beams were rapidly switched with a rising and damping times of 0.21 ms and 0.19 ms, respectively. Under the designed operating condition of 110 kVp and 15 mA, a dose rate of 8245 μGy s−1 was obtained at the detector surface with the inherent Al filtration and 2312 μGy s−1 with an additional 0.3 mm Cu filter. There was negligible change of the x-ray dose rate over many operating cycles. A ms-CBCT scan of an adult head phantom was completed in 14.4 s total exposure time for the imaging dose in the range of that of a clinical CBCT scanner. A spatially distributed CNT x-ray source array was designed and fabricated. It has enabled a new multisource CBCT to overcome some of the main inherent limitations of the conventional CBCT.

Cone-beam computed tomography (CBCT) dose optimization technique and image quality assessment scoring.

Linear accelerator (LINAC) embedded with kV source-imager system is capable to do image-guided radiotherapy. The only disadvantage of cone-beam computed tomography image acquisition during treatment is the extra radiation dose to the patient. The aim of this study is to optimize the CBCT imaging doses likely to be received by the patient undergoing radiotherapy without affecting image quality. The imaging dose to the patient was estimated on CTDI phantoms. The effect of additional filters of different materials (copper, brass, aluminum of thickness 0.1 mm each) was evaluated to find the optimized dose imaging technique. For the pelvis, a single imaging protocol available on the machine was used, whereas for the head and neck region, two protocols, high-quality head and standard-dose head were used. The image quality was assessed on CATPHAN-504 phantom using Owl CATPHAN® QA online tool. A new term "Image Assessment score" (IAS) was introduced to evaluate the image quality. In the pelvis protocol, CBCT imaging doses with an additional 0.1-mm brass, copper, and aluminum filter were measured to be reduced by 7.1%, 4.7%, and 2.5%, respectively, whereas for high-quality head protocol, the dose reduction was 25.4% (with brass filter), 22% (with copper filter), and 3.1% (with aluminum filter). For the standard-dose head protocol, doses were reduced by 7.5%, 2.8%, and 2.1% with additional 0.1-mm brass copper and aluminum filters, respectively. Acceptable image quality was observed with all the filters. Although the reconstructed images were found somewhat noisier, they did not affect the purpose of imaging, that is, treatment position verification. It was observed that these extra filters further reduce the imaging dose without much affecting the image quality.

Influence of the technical parameters of CBCT image acquisition on vertical root fracture diagnosis: a systematic review and meta-analysis.

To evaluate the influence of image acquisition parameters (voxel, FOV, kVp, mA) on the accuracy of cone-beam computed tomography (CBCT) in detecting vertical root fracture (VRF). Searches were performed in 6 main databases and the gray literature, without restrictions of language or date. Observational clinical studies (OCS) and in vitro-extracted teeth (IV) studies were considered eligible for inclusion when investigating the accuracy (sensitivity, specificity) of CBCT in detecting VRF in human teeth. The risk of bias was assessed using QUADAS-2, and a meta-analysis was performed using Review Manager v5.4 software and Jamovi software v1.6. A total of 60 out of 132 articles was included after fulfilling the eligibility criteria. Of these, 54 were IV studies while 6 were OCS. In the IV studies, it was seen that smaller FOV sizes tended to present higher accuracy values. The meta-analysis of the 6 OCS showed that the overall sensitivity and specificity values for 0.08mm and 0.1mm voxels were greater (0.84 and 0.79, respectively) than the sensitivity and specificity values for 0.125mm and 0.2mm voxels (0.70 and 0.55, respectively). Despite the uncertain risk of bias found for the IV and OCS studies, smaller voxel and FOV sizes seem to provide more accurate VRF detection values when using CBCT. This information is crucial for supporting the clinician when prescribing CBCT in cases of a clinical suspicion of VRF, and contributes to the personalization of the CBCT prescription, thereby ensuring greater accuracy in the VRF diagnosis. Registration This protocol was registered at the PROSPERO database (International Prospective Register of Systematic Review) under registration number CRD42020210118.

Current trends in the adoption and education of cone beam computed tomography and panoramic radiography machines across Australia.

This is a follow-up study to assess growth in the number of cone beam computed tomography (CBCT) and panoramic radiography (PR) machines in Australia. It is also the first study to evaluate the current status of both CBCT and PR education in Australia. CBCT and PR machine numbers were obtained from the radiation regulators across Australia. Australian dental schools were surveyed via email. The number of machines relative to population size and the number of dentists were calculated. In 2020, there were 706 CBCT machines and 3,059 PR machines, representing a 204.3% increase in the number of CBCT machines and an 82.0% increase in the number of PR machines over six years. Majority of Australian dental schools owned PR and CBCT machines. Most taught PR acquisition and interpretation, however only one-third taught CBCT image acquisition and interpretation to predoctoral students. CBCT machine numbers increased by nearly three-fold while PR machines only increased by 1.6 times over a six-year period relative to population size and number of dentists. Only very few Australian dental schools provide CBCT education to predoctoral students, raising concern as to whether graduates are adequately trained upon program completion.

Cone beam CT imaging for bronchoscopy: a technical review.

Cone beam computed tomography (CBCT) is a well-established imaging modality with numerous proven applications across multiple clinical disciplines. More recently, CBCT has emerged as an important imaging tool for bronchoscopists, primarily used during transbronchial biopsy of peripheral pulmonary lesions (PPLS). For this application CBCT has proved useful in navigating devices to a target lesion, in confirming device tool-in-lesion, as well as during tissue acquisition. In addition, CBCT is poised to play an important role in trials evaluating bronchoscopic ablation by helping to determine the location of the ablative probe relative to the target lesion. Before adopting this technology, it is key for bronchoscopists to learn some basic concepts that will allow them to have a safer and more successful experience with CBCT. Hence, in the current manuscript, we will focus on both technical and practical aspects of CBCT imaging, ranging from systems considerations, image quality, radiation dose and dose-reduction strategies, procedure room set-up, and best practices for CBCT image acquisition.

Dual cardiac and respiratory gated thoracic imaging via adaptive gantry velocity and projection rate modulation on a linear accelerator: A Proof-of-Concept Simulation Study.

Cardiac motion is typically not accounted for during pretreatment imaging for central lung and mediastinal tumors. However, cardiac induced tumor motion averages 5.8mm for esophageal tumors and 3-5 mm for some lung tumors, which can result in positioning errors. Our aim is to reduce both cardiac- and respiratory-induced motion artifacts in thoracic cone beam computed tomography (CBCT) images through gantry velocity and projection rate modulation on a standard linear accelerator (linac). The acquisition of dual cardiac and respiratory gated CBCT thoracic images was simulated using the XCAT phantom with patient-measured respiratory and ECG traces. The gantry velocity and projection rate were modulated based on the cardiac and respiratory signals to maximize the angular consistency between adjacent projections in the gated cardiac-respiratory bin. The mechanical limitations of a gantry-mounted CBCT system were investigated. For our protocol, images were acquired during the 60%-80% window of cardiac phase and 20% displacement either side of peak exhale of the respiratory cycle. The comparator method was the respiratory-only gated CBCT acquisition with constant gantry speed and projection rate in routine use for respiratory correlated four-dimensional (4D) CBCT. All images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. The methods were compared in terms of image sharpness as measured using the edge response width (ERW) and contrast as measured using the contrast to noise ratio (CNR). The effects of the total number of projections acquired and magnitude of cardiac motion on scan time and image quality were also investigated. Median total scan times with our protocol ranged from 117s (40 projections) through to 296s (100 projections), compared with 240s for the conventional protocol (1320 projections). The scan times were dictated by the number of projections acquired, heart rate, length of the respiratory cycle and mechanical constraints of the CBCT system. Our protocol was able to provide between 8% and 43% decrease in the median value of the ERW in the anterior/posterior (AP) direction across the 17 traces when there was 0.5cm of cardiac motion and between 35% and 64% decrease when there was 1.0cm of cardiac motion over conventional acquisition. In the superior-inferior (SI) direction, our protocol was able to provide between 22% and 26% decrease in the median value of the ERW across the 17 traces when there was 0.5cm of cardiac motion and between 30% and 35% decrease when there was 1.0cm of cardiac motion over conventional acquisition. The magnitude of the cardiac motion did not have an observable effect on the median value of the CNR. Across all 17 traces, our adaptive protocol produced noticeably more consistent, albeit lower CNR values compared with conventional acquisition. For the first time, the potential of adapting CBCT image acquisition to changes in the patient's cardiac and respiratory rates simultaneously for applications in radiotherapy was investigated. This work represents a step towards thoracic imaging that reduces the effects of both cardiac and respiratory motion on image quality.

McSART: an iterative model-based, motion-compensated SART algorithm for CBCT reconstruction

4D cone beam computed tomography (CBCT) images of the thorax and abdomen can have reduced quality due to the limited number of projections per respiratory bin used in gated image reconstruction. In this work, we present a new algorithm to reconstruct high quality CBCT images by simultaneously reconstructing images and generating an associated respiratory motion model. This is done by updating model parameters to compensate for motion during the iterative image reconstruction process. CBCT image acquisition was simulated using the digital eXternal CArdiac Torso (XCAT) phantom, simulating breathing motion using four patient breathing traces. 4DCBCT images were reconstructed using the simultaneous algebraic reconstruction technique (SART), and compared to the proposed motion-compensated SART (McSART) algorithm. McSART used a motion model that describes tissue position as a function of diaphragm amplitude and velocity. The McSART algorithm alternately updated the motion model and image reconstruction, increasing the number of projections used for image reconstruction with every iteration. The model was able to interpolate and extrapolate deformations according to the magnitude of the surrogate signal. Without noise, the final iteration McSART images had HU errors at 31%, 34%, and 44% of their SART-reconstructed counterparts compared to ground truth XCAT images, with corresponding root-mean-square (RMS) motion model errors of 0.75 mm, 1.08 mm, and 1.17 mm respectively. With added image noise, McSART’s HU error was 31% of the SART-reconstructed 4DCBCT error, with a 1.43 mm RMS motion model error. Qualitatively, blurring and streaking artifacts were reduced in all the reconstructed images compared to 3D or SART-reconstructed 4DCBCT. The output of the algorithm was a high quality reference image and a corresponding motion model, that could be used to deform the reference image to any other point in a breathing cycle.

P31. Commissioning, quality assurance and initial experience of a Calypso R system: Geneva experience

Introduction The Calypso R system (Varian medical systems), that uses radiofrequency signals for wireless tumor localization (absolute or relative to a zero set on the day) and tracking during radiotherapy, was installed in Geneva in 2015. Since January 2016 it is used to treat prostate patients (pts) with dynamic edge gating (allows to set motion thresholds which disable radiation delivery if the beacons, representing the target, move outside these thresholds). Here we present our early experience with its use with prostate implanted beacons as well as commissioning results and daily quality assurance (QA). Materials/methods For commissioning, specific tools were made available by the vendor. Furthermore our Rando R phantom was implanted with prostatic transponders to verify Calypso R versus cone beam computed tomography (CBCT) beacon’s position and isocenter correspondence as well as to realize an end-to end QA test (to export beacons info from CT scan, import etc). Commissioning QA involved checking: the system calibration and accuracy (isocenter Calypso R versus linac), the optical system monitoring the electro-magnetic array, the localization and tracking functionality, the dynamic edge gating, the correct creation of the reports and beam on radiation detection. Daily QA is performed with the QA fixture phantom and system calibration uses the Isocenter calibration fixture, both delivered with the system. Five patients with different targets are actually under treatment with volumetric modulated arc therapy plans (2 pts for whole prostate gland, 2 pts for pelvic lymph nodes + prostate and 1 pt for prostatic bed). Beacons are implanted with a trans-perineal procedure (not trans-rectal, as suggested by vendor). All patients are positioned supine with a feet immobilization and a knee cousin element on the dedicated Kevlar table top. Calypso R is first used to position the patient and to monitor CBCT image acquisition, for patient overall positioning, and after for patient tracking. Results Commissioning was made in half a day, with values within vendor’s specifications (Calypso R-Linac isocenter 0.1 cm). Daily QA shows a stability of the system (over more than 50 days, Calypso R-Linac isocenter 0.13 cm). Concerning patients, no beacons implant complications was registered, nor transponder migration seen on CBCT images or detected by Calypso R, even after several weeks of treatment. All patients could be treated using ”absolute” isocenter localization and tracking. Care was needed to position the array to avoid possible knee collisions if readjusting the patient or moving the table. When patient’s bladder and rectal filling reproduce simulation conditions, only 5 min extra are necessary to the session for array positioning, tracking and imaging. Clearly, one patient is reproducible on a daily basis (within 0.3 cm) and one patients shows a continuous drift of the tracking curve. Other patients do not present a distinct tracking curve behavior. Conclusions Overall Calypso R usage is easy and fast. A lower knee cousin will be used in the future to increase clearance between patient and array. Calypso R, detecting intra-fraction prostate movements, is introducing in our department a new way to perceive organ motion.

Measurement of eye lens dose for Varian On-Board Imaging with different cone-beam computed tomography acquisition techniques

The objective of this work was to measure patient eye lens dose for different cone-beam computed tomography (CBCT) acquisition protocols of Varian's On-Board Imaging (OBI) system using optically stimulated luminescence dosimeter (OSLD) and to study the variation in eye lens dose with patient geometry and distance of isocenter to the eye lens. During the experimental measurements, OSLD was placed on the patient between the eyebrows of both eyes in line of nose during CBCT image acquisition to measure eye lens doses. The eye lens dose measurements were carried out for three different cone-beam acquisition protocols (standard dose head, low-dose head [LDH], and high-quality head [HQH]) of Varian OBI. Measured doses were correlated with patient geometry and distance between isocenter and eye lens. Measured eye lens doses for standard head and HQH protocols were in the range of 1.8–3.2 mGy and 4.5–9.9 mGy, respectively. However, the measured eye lens dose for the LDH protocol was in the range of 0.3–0.7 mGy. The measured data indicate that eye lens dose to patient depends on the selected imaging protocol. It was also observed that eye lens dose does not depend on patient geometry but strongly depends on distance between eye lens and treatment field isocenter. However, undoubted advantages of imaging system should not be counterbalanced by inappropriate selection of imaging protocol, especially for very intense imaging protocol.

SU‐E‐J‐11: Measurement of Eye Lens Dose for Varian On‐Board Imaging with Different CBCT Acquisition Techniques

Purpose:To measure actual patient eye lens dose for different cone beam computed tomography (CBCT) acquisition protocol of Varian's On Board Imagining (OBI) system using Optically Stimulated Luminescence (OSL) dosimeter and study the eye lens dose with patient geometry and distance of isocenter to the eye lensMethods:OSL dosimeter was used to measure eye lens dose of patient. OSL dosimeter was placed on patient forehead center during CBCT image acquisition to measure eye lens dose. For three different cone beam acquisition protocol (standard dose head, low dose head and high quality head) of Varian On‐Board Imaging, eye lens doses were measured. Measured doses were correlated with patient geometry and distance between isocenter to eye lens.Results:Measured eye lens dose for standard dose head was in the range of 1.8 mGy to 3.2 mGy, for high quality head protocol dose was in range of 4.5mGy to 9.9 mGy whereas for low dose head was in the range of 0.3mGy to 0.7mGy. Dose to eye lens is depends upon position of isocenter. For posterioraly located tumor eye lens dose is less.Conclusion:From measured doses it can be concluded that by proper selection of imagining protocol and frequency of imaging, it is possible to restrict the eye lens dose below the new limit set by ICRP. However, undoubted advantages of imaging system should be counter balanced by careful consideration of imaging protocol especially for very intense imaging sequences for Adoptive Radiotherapy or IMRT

Digital reconstruction of high-quality daily 4D cone-beam CT images using prior knowledge of anatomy and respiratory motion

Conventional in-room cone-beam computed tomography (CBCT) lacks explicit representation of patient respiratory motion and usually has poor image quality and inaccurate CT numbers for target delineation and/or adaptive treatment planning. In-room four-dimensional (4D) CBCT image acquisition is still time consuming and suffers the same issue of poor image quality. To overcome this limitation, we developed a computational framework to digitally synthesize high-quality daily 4D CBCT images using the prior knowledge of motion and appearance learned from the planning 4D CT dataset. A patient-specific respiratory motion model was first constructed from the planning 4D CT images using principal component analysis of displacement vector fields across different respiratory phases. Subsequently, the respiratory motion model as well as the image content of the planning CT was spatially mapped onto the daily CBCT using deformable image registration. The synthesized 4D images possess explicit patient motion while maintaining the geometric accuracy of patient's anatomy at the time of treatment. We validated our model by quantitatively comparing the synthesized 4D CBCT against the 4D CT dataset acquired in the same day from protocol patients undergoing daily in-room CBCT setup and weekly 4D CT for treatment evaluation. Our preliminary results have demonstrated good agreement of contours in different motion phases between the synthesized and acquired scans. Various imaging artifacts were also suppressed and soft-tissue visibility was enhanced.

CBCT-based volume of simulated root resorption - influence of FOV and voxel size.

To examine the influence of the field of view (FOV) and voxel size on the measurement of the volume of simulated internal root resorption (IRR) lesions through cone-beam computed tomography (CBCT). Eleven single-rooted teeth with IRR simulated by acid demineralization were studied. CBCT images were acquired using large FOV (voxel sizes of 0.200, 0.250 and 0.300 mm) and limited FOV (voxel sizes of 0.076, 0.100 and 0.200 mm). The IRR volumes were calculated using the Dolphin(®) software. Volumetric measurements were validated using IRR silicone putty casts. The analysis of variance (anova) for randomized block design complemented with the Tukey's test was employed. IRR volumes obtained using voxel sizes of 0.200 and 0.250 mm were similar (P > 0.05). However, both these values were significantly different from that obtained using the 0.300-mm voxel (P < 0.05). There was no significant difference between IRR volumes measured through voxel sizes of 0.076 and 0.100 mm (P > 0.05), but both differed significantly from that obtained through the 0.200-mm voxel (P < 0.05). There was no significant difference between the volumetric measurements of the 0.200-mm voxel images of the restricted and large FOV protocols. The mean volumes of the silicone casts were smaller than those calculated using a 0.200-mm voxel, but were similar to those obtained using voxel sizes of 0.076 and 0.300 mm. Despite the FOV protocol, voxel size can influence measurement of simulated IRR volumes. The importance of standardization of CBCT image acquisition protocols is emphasized, especially during follow-up of an IRR lesion, to prevent misinterpretation of its extent, which can create a bias in clinical decisions.

Usefulness of Cone-Beam Computed Tomography in Determining the Position of Ossicular Prostheses

Cone-beam computed tomography (CT) is proving useful in various operative settings. We hypothesize that it has great potential as an intraoperative assessment tool for ossicular prosthesis positioning. Results from prosthetic ossiculoplasty are frequently disappointing. Undetected intraoperative displacement of the prosthesis may be caused, and obscured, by placement of an overlying cartilage graft. A cadaveric right temporal bone was prepared with a tympanomeatal flap, and an extended posterior tympanotomy through a cortical mastoidectomy. Each of 3 commercially available prostheses was positioned in 3 different locations: (1) optimal, (2) grossly displaced, and (3) marginally displaced. The intended prosthetic positions were confirmed by endoscopy before and after cone-beam CT image acquisition. The primary outcome measure was the position of the prosthesis in relation to the stapes and tympanic membrane, as assessed by 5 expert reviewers blinded to the study. Secondary outcome measures included optimal dosing for adequate image resolution and radiographic scatter associated with different prosthetic materials. Cone-beam CT accurately demonstrated the position of ossicular reconstruction prostheses with respect to the stapes and tympanic membrane. Prosthesis displacement, whether minimally or marked, was also accurately demonstrated. Interobserver agreement among the 5 reviewers, measured using a Fleiss κ statistic, ranged from 0.4 to 0.8 (fair to substantial agreement depending on type and position of the prosthesis). Cone-beam CT is a useful tool for determining the position of ossicular reconstruction prostheses in situ. We suggest it has potential for intraoperative assessment, to check positioning after the prosthesis has been covered with a cartilage graft and tympanomeatal flap.

Reference radiochromic film dosimetry in kilovoltage photon beams during CBCT image acquisition

A common approach for dose assessment during cone beam computed tomography (CBCT) acquisition is to use thermoluminescent detectors for skin dose measurements (on patients or phantoms) or ionization chamber (in phantoms) for body dose measurements. However, the benefits of a daily CBCT image acquisition such as margin reduction in planning target volume and the image quality must be weighted against the extra dose received during CBCT acquisitions. The authors describe a two-dimensional reference dosimetry technique for measuring dose from CBCT scans using the on-board imaging system on a Varian Clinac-iX linear accelerator that employs the XR-QA radiochromic film model, specifically designed for dose measurements at low energy photons. The CBCT dose measurements were performed for three different body regions (head and neck, pelvis, and thorax) using humanoid Rando phantom. The authors report on both surface dose and dose profiles measurements during clinical CBCT procedures carried out on a humanoid Rando phantom. Our measurements show that the surface doses per CBCT scan can range anywhere between 0.1 and 4.7 cGy, with the lowest surface dose observed in the head and neck region, while the highest surface dose was observed for the Pelvis spot light CBCT protocol in the pelvic region, on the posterior side of the Rando phantom. The authors also present results of the uncertainty analysis of our XR-QA radiochromic film dosimetry system. Radiochromic film dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one-sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on film exposure calibration in terms of "air kerma in air," which simplifies both the calibration procedure and reference dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR-QA film dose at the surface into dose to water (or water kerma) at the surface of the phantom indicate that, for typical beam qualities used in CBCT, this conversion can be approximated by simple mass-energy absorption coefficient ratios water-to-air.

Monte Carlo simulation and patient dosimetry for a kilovoltage cone‐beam CT unit

The purpose of this work is to characterize the x-ray volume imager (XVI), the cone-beam computed tomography (CBCT) unit mounted on the Elekta Synergy linac, with F1 bowtie filter and to calculate the three-dimensional dose delivered to patients using volumetric acquisition. The XVI is modeled in detail using a new Monte Carlo (MC) code, BEAMPP, under development at the National Research Council Canada. In this investigation, a new component module is developed to accurately model the unit's bowtie filter used in conjunction with the available beam collimators at the clinical energy of 120 kV. The modeling is compared against percentage depth dose (PDD) and profile measurements. Kilovoltage radiation beams' phase space files are also analyzed. The authors also describe a method for the absolute dose calibration of the MC model of the CBCT unit when used in a clinical volumetric acquisition mode. Finally, they calculate three-dimensional patient dose from CBCT image acquisition in three clinical cases of interest: Pelvis, lung, and head and neck. The agreement between measurement and MC is shown to be very good: Within +/- 2% for the PDD and within +/- 3.5% inside the radiation field for all the collimators with the F1 bowtie filter. A full account of the absolute calibration method is given and dose calculation is validated against ion chamber measurements in different locations of a plastic phantom. Calculations and experiments agree within +/- 2% or better in both at the center and the periphery of the phantom, with worst agreement of 4.5% at the surface of the phantom and for one specific combination of collimator and filter. Patient dose from CBCT scan reveals that dose to tissue is between 2 and 2.5 cGy for a pelvis or a lung full acquisition. For H&N dose to tissue is 5 cGy, with the unit presets used in this work. Dose to bony structures can be two to three times higher than dose to tissue. The XVI CBCT unit has been fully modeled including the F1 bowtie filter. Absolute dose distribution from the unit has been successfully validated. Full MC patient dose calculation has shown that the three-dimensional dose distribution from CBCT is complex. Patient dose from CBCT exposure cannot be completely accounted for by using a numerical factor as an estimate of the dose at the center of the body. Furthermore, additional dose to bone should be taken into account when adopting any IGRT strategy and weighed vs the unquestionable benefits of the technique in order to optimize treatment. Full three-dimensional dose calculation is recommended if patient dose from CBCT is to be integrated in any adaptive planning strategy.