Cone Beam CT Dose Research Articles

Estimation of secondary cancer projected risk after partial breast irradiation at the 1.5 T MR-linac

PurposeFor patients treated with partial breast irradiation (PBI), potential long-term treatment-related toxicities are important. The 1.5 T magnetic resonance guided linear accelerator (MRL) offers excellent tumor bed visualization and a daily treatment plan adaption possibility, but MRL-specific electron stream and return effects may cause increased dose deposition at air–tissue interfaces. In this study, we aimed to investigate the projected risk of radiation-induced secondary malignancies (RISM) in patients treated with PBI at the 1.5 T MRL.MethodsProjected excess absolute risk values (EARs) for the contralateral breast, lungs, thyroid and esophagus were estimated for 11 patients treated with PBI at the MRL and compared to 11 patients treated with PBI and 11 patients treated with whole breast irradiation (WBI) at the conventional linac (CTL). All patients received 40.05 Gy in 15 fractions. For patients treated at the CTL, additional dose due to daily cone beam computed tomography (CBCT) was simulated. The t‑test with Bonferroni correction was used for comparison.ResultsThe highest projected risk for a radiation-induced secondary cancer was found for the ipsilateral lung, without significant differences between the groups. A lower contralateral breast EAR was found for MRL-PBI (EAR = 0.89) compared to CTL-PBI (EAR = 1.41, p = 0.01), whereas a lower thyroid EAR for CTL-PBI (EAR = 0.17) compared to MRL-PBI (EAR = 0.33, p = 0.03) and CTL-WBI (EAR = 0.46, p = 0.002) was observed. Nevertheless, when adding the CBCT dose no difference between thyroid EAR for CTL-PBI compared to MRL-PBI was detected.ConclusionBetter breast tissue visualization and the possibility for daily plan adaption make PBI at the 1.5 T MRL particularly attractive. Our simulations suggest that this treatment can be performed without additional projected risk of RISM.

A simulated comparison of lung tumor target verification using stereoscopic tomosynthesis or radiography.

Mobile lung tumors are increasingly being treated with ablative radiotherapy, for which precise motion management is essential. In-room stereoscopic radiography systems are able to guide ablative radiotherapy for stationary cranial lesions but not optimally for lung tumors unless fiducial markers are inserted. We propose augmenting stereoscopic radiographic systems with multiple small x-ray sources to provide the capability of imaging with stereoscopic, single frame tomosynthesis. In single frame tomosynthesis, nine x-ray sources are placed in a 3×3 configuration and energized simultaneously. The beams from these sources are collimated so that they converge on the tumor and then diverge to illuminate nine non-overlapping sectors on the detector. These nine sector images are averaged together and filtered to create the tomosynthesis effect. Single frame tomosynthesis is intended to be an alternative imaging mode for existing stereoscopic systems with a field of view that is three times smaller and a temporal resolution equal to the frame rate of the detector. We simulated stereoscopic tomosynthesis and radiography using Monte Carlo techniques on 60 patients with early-stage lung cancer from the NSCLC-Radiomics dataset. Two board-certified radiation oncologists reviewed these simulated images and rated them on a 4-point scale (1: tumor not visible; 2: tumor visible but inadequate for motion management; 3: tumor visible and adequate for motion management; 4: tumor visibility excellent). Each tumor was independently presented four times (two viewing angles from radiography and two viewing angles from tomosynthesis) in a blinded fashion over two reading sessions. The fraction of tumors that were rated as adequate or excellent for motion management (scores 3 or 4) from at least one viewing angle was 53% using radiography and 90% using tomosynthesis. From both viewing angles, the corresponding fractions were 7% for radiography and 48% for tomosynthesis. Readers agreed exactly on 62% of images and within 1 point on 98% of images. The acquisition technique was estimated to be 75 mAs at 120 kVp per treatment fraction assuming one verification image per breath, approximately one order of magnitude less than a standard dose cone beam CT. Stereoscopic tomosynthesis may provide a noninvasive, low dose, intrafraction motion verification technique for lung tumors treated by ablative radiotherapy. The system architecture is compatible with real-time video capture at 30 frames per second. Simulations suggest that most, but not all, lung tumors can be adequately visualized from at least one viewing angle.

The Effects of Additional Filtration on Image Quality and Radiation Dose in Cone Beam CT: An In Vivo Preliminary Investigation.

Purpose The aim of this study was to investigate the effect of reduced radiation doses on the image quality of cone-beam computed tomography scans and the suitability of such imaging for orthodontics, oral surgery, dental implantology, periodontology, and endodontology. Materials and Methods Cone-beam computed tomography scans of a live patient were performed using seven attenuation filters with increased thickness to decrease the effective radiation dose from 22.4 to 1.8 μSv, and the effects of different radiation doses on image quality were further analysed. Quantitative image quality was calculated using dedicated measures, such as signal and contrast-to-noise ratio and sharpness. A panel of five certified raters assessed the cone-beam computed tomography scans qualitatively. Nine anatomical structures relevant to dentistry were identified, and the overall acceptance was assessed. Results Linear reduction of the effective radiation dose had a nonlinear effect on image quality. A 5-fold reduction in the effective dose led to acceptable quantitative and qualitative image quality measures, and the identification rate of dental anatomical structures was 80% or greater. The use of less than 40% of the reference dose was unacceptable for all dental specialties. Conclusions The ideal radiation dose for specific diagnostic requirements remains a patient-related and specialty-related decision that must be made on an individual basis. Based on the results of this study, it is possible to reduce exposure in selected patients, and at the same time obtain sufficient quality of images for clinical purposes.

Dose assessment for daily cone-beam CT in lung radiotherapy patients and its combination with treatment planning.

With the increased use of X-ray imaging for patient alignment in external beam radiation therapy, particularly with cone-beam computed tomography (CBCT), the additional dose received by patients has become of greater consideration. In this study, we analysed the radiation dose from CBCT for clinical lung radiotherapy and assessed its relative contribution when combined with radiation treatment planning for a variety of lung radiotherapy techniques. The Monte Carlo simulation program ImpactMC was used to calculate the 3D dose delivered by a Varian TrueBeam linear accelerator to patients undergoing thorax CBCT imaging. The concomitant dose was calculated by simulating the daily CBCT irradiation of ten lung cancer patients. Each case was planned with a total dose of 50-60Gy to the target lesion in 25-30 fractions using the 3DCRT or IMRT plan and retrospectively planned using VMAT. For each clinical case, the calculated CBCT dose was summed with the planned dose, and the dose to lungs, heart, and spinal cord were analysed according to conventional dose conformity metrics. Our results indicate greater variations in dose to the heart, lungs, and spinal cord based on planning technique, (3DCRT, IMRT, VMAT) than from the inclusion of daily cone-beam imaging doses over 25-30 fractions. The average doses from CBCT imaging per fraction to the lungs, heart and spinal cord were 0.52 ± 0.10, 0.49 ± 0.15 and 0.39 ± 0.08cGy, respectively. Lung dose variations were related to the patient's size and body composition. Over a treatment course, this may result in an additional mean absorbed dose of 0.15-0.2Gy. For lung V5, the imaging dose resulted in an average increase of ~ 0.6% of the total volume receiving 5Gy. The increase in V20 was more dependent on the planning technique, with 3DCRT increasing by 0.11 ± 0.09% with imaging and IMRT and VMAT increasing by 0.17 ± 0.05% and 0.2 ± 0.06%, respectively. In this study, we assessed the concomitant dose for daily CBCT lung cancer patients undergoing radiotherapy. The additional radiation dose to the normal lungs from daily CBCT was found to range from 0.15 to 0.2Gy when the patient was treated with 25-30 fractions. Consideration of potential variation in relative biological effectiveness between kilovoltage imaging and megavoltage treatment dose was outside the scope of this study. Regardless of this, our results show that the assessment of imaging dose can be incorporated into the treatment planning process and the relative effect on overall dose distribution was small compared to the difference among planning techniques.

An Analysis of Daily Setup Variation in Prone Breast Radiation of Early-Stage Breast Cancer

For women with left-sided breast cancer, the most relevant side effect is collateral damage to the heart with radiation therapy. Prone treatment techniques have helped reduce heart dose, but is more unstable and difficult to replicate. Setup uncertainties can lead to higher than expected heart doses or under-dosing of breast tissue. Our objective was to investigate the potential dosimetric benefit of utilizing a low dose cone beam CT (CBCT) in the daily setup of prone left breast radiation.We performed a retrospective review patients treated at our institution between April 2019 and February 2020 in the prone position for left sided early-stage breast cancer. Patients were set up to clinical marks and a custom low dose partial arc CBCT was acquired with each fraction. Using the daily shifts, we calculated the delivered dose if these shifts were not performed. Differences between planned and pre-CBCT shift doses were recorded for the heart and breast tissue. Patients were grouped into 3 outcomes: (A) Significantly high heart dose: More than 10% increase in delivered heart dose from planned; (B) Poor Breast Coverage: More than 5% decrease in the volume receiving 90% of the prescription dose; or (C) Minimal Variation: No significant increase in heart dose or decrease in breast coverage. Patient factors were also collected. Statistical comparisons were made using t-tests.18 patients were included, with 283 daily CBCT shifts and an average of 15.8 CBCT's per patient (range 13-25). The mean age of the patients was 61.6 (39-80) and average BMI 28.3 (20.3 - 45). Breast and heart dose were available for 196 scans, of which 47 (24%) had high heart dose (A), 55 (28%) had poor breast coverage and only 98 (50%) had no more than minimal variation in either. Patients with breast size < 1000 cc had a 64.5% chance of a delivery with poor breast coverage or increased heart dose as opposed to 40% for women with larger breast (P < 0.01). The same relationship was seen for weight (P < 0.01), refer to Table 1. When combining the total dose for each patient, 3 (17%) patients were in group A (increased heart dose), 9 patients (50%) were in group B (poor breast coverage) and 6 patients (33%) were in group C. Patients with minimal variation had significantly higher weight (84 kg vs 66 kg, P = 0.038), BMI (33 vs 26, P = 0.03) and breast volumes (1716 cc vs 992 cc, P = 0.01).Overall, our study demonstrated significant variation in daily setup for patients receiving prone breast radiation. Only half of treatments would have been delivered with minimal variation and a majority of patients would have either received significantly increased heart dose or suboptimal breast coverage if setup errors were not corrected. Likelihood of a significant setup error was seen most in women with smaller breasts or lower weight.

THE MICROBIOME - A KEY REGULATOR OF MENTAL HEALTH ACROSS LIFESPAN

Accurate Cone Beam CT (CBCT) based dose calculations are hindered by limited CBCT image quality. Using retrospective artefact corrections, this paper investigated the accuracy of dose calculations performed directly on CBCT images of lung cancer patients.Dose calculations were made directly on clinical and artefact corrected CBCT images of 21 lung cancer patients with a re-simulation CT (rCT) image acquired during radiotherapy. The original treatment plan was copied to the rCT and CBCT images and dose was recalculated. Dose comparisons were made using gamma analysis and dose statistics. Gamma comparisons were made using 2%/2 mm and 1%/1 mm criteria, and pass rates of the clinical and improved CBCT images were calculated using the rCT based dose as reference.Dose distributions calculated on the artefact corrected CBCT images had a median 2%/2 mm gamma pass rate of 99.4% when compared to the reference rCT. Doses calculated on the clinical CBCT images had a median 2%/2 mm gamma pass rate of 93.1%. Wilcoxon signed rank test showed the pass rates in the entire CBCT field of view different at p<0.001. Clinical CBCT image based dose calculations overestimated the dose, while the improved CBCT doses were in closer agreement with the rCT doses.Comprehensive artefact correction of CBCT images allowed highly accurate dose calculations to be performed directly on CBCT images of lung cancer patients, following the standard CT-based workflow in a treatment planning system.

A cloud-fog software architecture for dental CBCT dose monitoring using the DICOM structured report: Automated establishment of DRL.

The diagnostic reference level (DRL) has been established to optimize the diagnostic methods and reduce radiation dose during radiographic examinations. The aim of this study was to present a completely new solution based on Cloud-Fog software architecture for automatic establishment of the DRL values during dental cone-beam computed tomography (CBCT) according to digital imaging and communications in medicine (DICOM) structured reports. A Cloud-Fog software architecture was used for automatic data handling. This architecture used the DICOM structured reports as a source for extracting the required information by fog devices in the imaging center. These devices transferred the derived information to the cloud server. The cloud server calculated the value of indication-based DRL in dental CBCT imaging based upon the parameters and adequate quantities of the absorbed dose. The feedback of DRL value was continuously announced to the imaging centers in 6 phases. In each phase, the level of the dose was optimized in imaging centers. The DRL value was established for 5-specific indications, including third molar teeth (511mGy.cm2), implant (719mGy.cm2), form and position anomalies of the tooth (408mGy.cm2), dentoalveolar pathologies (612mGy.cm2), and endodontics (632mGy.cm2). The determination of the DRL value in each phase revealed a downward trend until stabilization. The new solution presented in this study makes it possible to calculate and update the DRL value nationally and automatically among all centers. Also, the results showed that this approach is successful in establishing stabilized DRL values.

Precision of orthodontic cephalometric measurements on ultra low dose-low dose CBCT reconstructed cephalograms

ObjectivesTo analyze differences in variation of orthodontic diagnostic measurements on lateral cephalograms reconstructed from ultra low dose-low dose (ULD-LD) cone beam computed tomography (CBCT) scans (RLC) as compared to variation of measurements on standard lateral cephalograms (SLC), and to determine if it is justifiable to replace a traditional orthodontic image set for an ULD-LD CBCT with a reconstructed lateral cephalogram.Material and methodsULD-LD CBCT images and SLCs were made of forty-three dry human skulls. From the ULD-LD CBCT dataset, a lateral cephalogram was reconstructed (RLC). Cephalometric landmarks (13 skeletal and 7 dental) were identified on both SLC and RLC twice in two sessions by two calibrated observers. Thirteen cephalometric variables were calculated. Variations of measurements, expressed as standard deviations of the 4 measurements on SLC and RLC, were analyzed using a paired sample t-test. Differences in the number of observations deviating ≥ 2.0 mm or degrees from the grand mean between SLC and RLC were analyzed using a McNemar test.ResultsMean SDs for 7 out of 13 variables were significantly smaller for SLCs than those for RLCs, but differences were small. For 9 out of 13 variables, there was no significant difference between SLC and RLC for the number of measurements outside the range of 2 mm or degrees.ConclusionsBased on the lower radiation dose and the small differences in variation in cephalometric measurements on reconstructed LC compared to standard dose LC, ULD-LD CBCT with reconstructed LC should be considered for orthodontic diagnostic purposes.Clinical relevanceULD-LD CBCT with reconstructed LC should be considered for orthodontic purposes.

A study of dose indicators during intra-arterial catheter implantation for liver chemotherapy

The aim of the present study was to describe patient dose indicator levels during intra-arterial catheter (IAC) implantation for liver chemotherapy, and to determine factors affecting the dose indicators. Between January 2017 and January 2019, 61 patients with hepatic metastases from colorectal cancer were retrospectively included. Interventions were carried out in a standardised manner by three experienced radiologists on the same angiographic table without changes in protocol parameters. For each patient, clinical, radiological and dosimetry data were collected, including the air kerma area product (KAP), part of KAP due to the fluoroscopy and fluoroscopy time (FT), total kerma at the reference interventional point and peak skin dose (PSD). Local dose reference levels (RLs) were determined as the third quartile of the patient dose distributions. Univariate and multivariate analysis of factors affecting dose indicators was performed. The mean KAP was 111 Gy cm2, the mean reference point air kerma (Ka,r) was 648 mGy, the mean PSD was 613 mGy, and the mean FT was 3190 s (62% of the KAP). The mean cone beam computed tomography dose was 37.3 ± 11.8 Gy cm2, which accounted for 37% of the KAP. The RL could be proposed taking into account the third quartiles (KAP = 164.6 Gy cm2, Ka,r = 904.5 mGy, FT = 4011 s and standard deviation = 772.7 mGy). The factors affecting dose indicators were related to the patients (sex, cardiovascular risk factors, weight, body mass index), to the vascular anatomies (coeliac trunk angulation) and to the procedures (number of embolised arteries). This study allowed a better understanding of dose indicators and factors affecting these indicators during the implantation of IACs for hepatic chemotherapy, which is a long and difficult procedure. Local dose RLs were determined. Multicentre, multi-equipment studies are necessary.

Effect of computed tomography value error on dose calculation in adaptive radiotherapy with Elekta X-ray volume imaging cone beam computed tomography.

PurposeWe evaluated the effect of changing the scan mode of the Elekta X‐ray volume imaging cone beam computed tomography (CBCT) on the accuracy of dose calculation, which may be affected by computed tomography (CT) value errors in three dimensions.MethodsWe used the electron density phantom and measured the CT values in three dimensions. CT values were compared with planning computed tomography (pCT) values for various materials. The evaluated scan modes were for head and neck (S‐scan), chest (M‐scan), and pelvis (L‐scan) with various collimators and filter systems. To evaluate the effects of the CT value error of the CBCT on dose error, Monte Carlo calculations of dosimetry were performed using pCT and CBCT images.ResultsThe L‐scan had a CT value error of approximately 800 HU at the isocenter compared with the pCT. Furthermore, inhomogeneity in the longitudinal CT value profile was observed in the bone material. The dose error for ±100 HU difference in CT values for the S‐scan and M‐scan was within ±2%. The center of the L‐scan had a CT error of approximately 800 HU and a dose error of approximately 6%. The dose error of the L‐scan occurred in the beam path in the case of both single field and two parallel opposed fields, and the maximum error occurred at the center of the phantom in the case of both the 4‐field box and single‐arc techniques.ConclusionsWe demonstrated the three‐dimensional CT value characteristics of the CBCT by evaluating the CT value error obtained under various imaging conditions. It was found that the L‐scan is considerably affected by not having a unique bowtie filter, and the S‐scan without the bowtie filter causes CT value errors in the longitudinal direction. Moreover, the CBCT dose errors for the 4‐field box and single‐arc irradiation techniques converge to the isocenter.

PD-0757 Low dose cone beam CT for paediatric image-guided radiotherapy: how much dose is enough?

PD-0757 Low dose cone beam CT for paediatric image-guided radiotherapy: how much dose is enough?

Feasibility evaluation of kilovoltage cone-beam computed tomography dose calculation following scatter correction: investigations of phantom and representative tumor sites.

BackgroundTo study the feasibility of kilovoltage cone-beam computed tomography (KV-CBCT) dose calculation following scatter correction.MethodsCIRS 062 and Catphan 504 phantoms were used in this study, and 40 randomly selected subjects representing a variety of cases (ten head cancer cases, ten chest cancer cases, ten abdominal cancer cases and ten pelvic cavity cancer cases) were enrolled. We developed in-house software called the cone-beam CT imaging toolkit (CITK) to improve the quality of CBCT images. We first aligned each planning computed tomography (pCT) image with the corresponding CBCT image using rigid registration after scatter correction. Hounsfield unit-relative electron density (HU-RED) calibration was applied to the CBCT images. The pCT plan was then recalculated on CBCT images. Finally, the dosimetric differences between the two plans were evaluated. The dosimetric parameters included the D98, D2, Dmean, conformity index (CI), homogeneity index (HI) and other organ at risk (OAR) dose parameters of the planning target volume (PTV). The dose distribution index (DDI) and the gamma index were also assessed. Paired Student’s t-tests or Wilcoxon rank tests were used to evaluate differences. P<0.05 was considered significant.ResultsIn the phantom and patient cases, the average dosimetric difference was less than 1% in the PTV and OARs. There was no significant difference in the CI or HI between the two plans. The gamma pass rate of 2%/2 mm was greater than 95% in both plans. There was a significant difference in the DDI between the two plans in the chest group but not in the other groups.ConclusionsThe results suggest that CBCT has high accuracy in dose calculation via scatter correction and HU-RED calibration.

Low dose cone beam CT for paediatric image-guided radiotherapy: Image quality and practical recommendations

PurposeCone beam CT (CBCT) is used in paediatric image-guided radiotherapy (IGRT) for patient setup and internal anatomy assessment. Adult CBCT protocols lead to excessive doses in children, increasing the risk of radiation-induced malignancies. Reducing imaging dose increases quantum noise, degrading image quality. Patient CBCTs also include ‘anatomical noise’ (e.g. motion artefacts), further degrading quality. We determine noise contributions in paediatric CBCT, recommending practical imaging protocols and thresholds above which increasing dose yields no improvement in image quality. Methods and materialsSixty CBCTs including the thorax or abdomen/pelvis from 7 paediatric patients (aged 6–13 years) were acquired at a range of doses and used to simulate lower dose scans, totalling 192 scans (0.5–12.8 mGy). Noise measured in corresponding regions of each patient and a 10-year-old phantom were compared, modelling total (including anatomical) noise, and quantum noise contributions as a function of dose. Contrast-to-noise ratio (CNR) was measured between fat/muscle. Soft tissue registration was performed on the kidneys, comparing accuracy to the highest dose scans. ResultsQuantum noise contributed <20% to total noise in all cases, suggesting anatomical noise is the largest determinant of image quality in the abdominal/pelvic region. CNR exceeded 3 in over 90% of cases ≥ 1 mGy, and 57% of cases at 0.5 mGy. Soft tissue registration was accurate for doses > 1 mGy. ConclusionAnatomical noise dominates quantum noise in paediatric CBCT. Appropriate soft tissue contrast and registration accuracy can be achieved for doses as low as 1 mGy. Increasing dose above 1 mGy holds no benefit in improving image quality or registration accuracy due to the presence of anatomical noise.

CBCT imaging: a simple approach for optimising and evaluating concomitant imaging doses, based on patient-specific attenuation, during radiotherapy pelvis treatment.

Objectives:A simple, robust method, for optimising cone-beam CT (CBCT) dose and image quality for pelvis treatment, based on patient-specific attenuation.Methods:Methods were investigated for grouping patients into four imaging categories (small [S], medium [M], large [L], extra large [XL]), based on planning-CT CTDIvol, and phantoms constructed to represent each group. CBCTs with varying kV, mA and ms honed in on the best settings, with a bladder noise of 25 HU. A patient pilot study clinically verified the new imaging settings.Results:The planning CTDIvol is a reliable method for grouping patients. Phantom measurements from the S, M and L groups show doses significantly reduced (19–83% reduction), whilst the XL group required an increase of 39%. Phantom TLD measurements showed the number of scans needed to increase rectal organ at risk (OAR) dose by 1 Gy was 143 (S group) and 50 (M group). Images were qualitatively assessed as sufficient by clinicians.Conclusion:Patient-specific CBCT modes are in use clinically with dose reductions across all modes except Pelvis XL, keeping doses ALARP and images optimal. Consideration of OAR doses controls the number of CBCTs allowed to ensure adherence to OAR tolerance. Reporting CBCT doses in “scans per Gray” allows clinicians to make informed decisions regarding the imaging schedule and concomitant doses.Advances in knowledge:Patient grouping at planning CT, using CTDIvol, allows for CBCT imaging protocols to be selected based on patient specific attenuation. Reporting OAR doses in terms of “scans per Gray” allows translation of imaging dose risk to the Oncologist.

Density calibrated cone beam CT as a tool for adaptive radiotherapy

Background Visual inspections of anatomical changes observed on daily cone-beam CT (CBCT) images are often used as triggers for radiotherapy plan adaptation to avoid unacceptable dose levels to the target or OARs. Direct CBCT dose calculations would improve the ability to adapt only those plans where dosimetric changes are observed. This study investigates the accuracy of dose calculations on CBCTs. Materials and methods Calibration curves were obtained for CBCT imagers at nine identical accelerators. CBCT scans of a phantom with different density inserts were recorded for two scan modes (Head-Neck and Pelvis) and mean calibration curves were calculated. Subsequently, CBCT scans of the phantom with six different density inserts were recorded, the dose distributions on the CBCTs were calculated and compared to dose on the planning CT (pCT). The uncertainty was quantified by the dosimetric difference between the pCT and the CBCT. The two mean calibration curves were used to calculate the daily delivered CBCT dose for ten Head-Neck-, eleven Lung-, and ten pelvic patients. Additional patient calculations were performed using low-HU empirically corrected calibration curves. Patient doses were compared on target coverage and mean dose, and D1cc for OARs. Results The dose differences between pCT and CBCT for phantom data were small for all DVH parameters, with mean deviations below ±0.6% for both CBCT modes. For patient data, it was found that low-HU corrected calibration curves performed the best. The mean deviations for the mean dose and coverage of the target were 0.2%±0.7% and 0.1%±0.6%, across all patient groups. Conclusion Dose calculation on CBCT images results in target coverage and mean dose with an accuracy of the order of 1%, which makes this acceptable for clinical use. The CBCT mode specific calibration curves can be used at all identical imaging devices and for all patient groups.

Dose Estimation by Geant4-Based Simulations for Cone-Beam CT Applications: A Systematic Review

The last two decades have witnessed increasing use of X-ray imaging and, hence, the exposure of humans to potentially harmful ionizing radiation. Computed tomography accounts for the largest portion of medically-related X-ray exposure. Accurate knowledge of ionizing radiation dose from Cone-Beam CT (CBCT) imaging is of great importance to estimate radiation risks and justification of imaging exposures. This work aimed to review the published evidence on CBCT dose estimation by focusing on studies that employ Geant4-based toolkits to estimate radiation dosage. A systematic review based on a scientometrics approach was conducted retrospectively, from January 2021, for a comprehensive overview of the trend, thematic focus, and scientific production in this topic. The search was conducted using WOS, PubMed, and Scopus databases, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. In total, 93 unique papers were found, of which only 34 met the inclusion criteria. We opine that the findings of this study provides a basis to develop accurate simulations of CBCT equipment for optimizing the trade-off between clinical benefit and radiation risk.

Surgivisio® and O-arm®O2 cone beam CT mobile systems for guidance of lumbar spine surgery: Comparison of patient radiation dose.

To compare patient radiation doses in cone beam computed tomography (CBCT) of two mobile systems used for navigation-assisted mini-invasive orthopedic surgery: O-arm®O2 and Surgivisio®. The study focused on imaging of the spine. Thermoluminescent dosimeters were used to measure organs and effective doses (ED) during CBCT. An ionization-chamber and a solid-state sensor were used to measure the incident air-kerma (Ki) at the center of the CBCT field-of-view and Ki during 2D-imaging, respectively. The PCXMC software was used to calculate patient ED in 2D and CBCT configurations. The image quality in CBCT was evaluated with the CATPHAN phantom. The experimental ED estimate for the low-dose 3D-modes was 2.41 and 0.35mSv with O-arm®O2 (Low Dose 3D-small-abdomen) and Surgivisio® (3DSU-91 images), respectively. PCXMC results were consistent: 1.54 and 0.30mSv. Organ doses were 5 to 12 times lower with Surgivisio®. Ki at patient skin were comparable on lateral 2D-imaging (0.5mGy), but lower with O-arm®O2 on anteroposterior (0.3 versus 0.9mGy). Both systems show poor low contrast resolution and similar high contrast spatial resolution (7 line-pairs/cm). This study is the first to evaluate patient ED and organ doses with Surgivisio®. A significant difference in organs doses was observed between the CBCT systems. The study demonstrates that Surgivisio® used on spine delivers approximately five to six times less patient ED, compared to O-arm®O2, in low dose 3D-modes. Doses in 2D-mode preceding CBCT were higher with Surgivisio®, but negligible compared to CBCT doses under the experimental conditions tested.

How low can you go? A CBCT dose reduction study.

PurposeCone beam computed tomography (CBCT) is often used for patient setup based solely on bony anatomy. The goal of this work was to evaluate whether CBCT dose can be lowered to the level of kV image pair doses when used for bony anatomy‐based IGRT without compromising positioning accuracy.MethodsAn anthropomorphic phantom was CT scanned in the head, head and neck, chest, and pelvis regions and setup on the linear accelerator couch with the isocenter near the planned location. Cone beam computed tomographies were performed with the standard “full dose” protocol supplied by the linac vendor. With sequentially lowering the dose, three‐dimensional (3D) matching was performed for each without shifting the couch. The standard kV image pair protocol for each site was also used to image the phantoms. For all studies, six degrees of freedom was included in the 2D or 3D matching to the extent they could be employed. Imaging doses were determined in air at isocenter following the TG‐61 formalism.ResultsCone beam computed tomography dose was reduced by 81–98% of the standard CBCT protocol to nearly that of the standard kV image pair dose for each site. Relative to the standard CBCT shift values, translational shifts were within 0.3 and 1.6 mm for all sites, for the reduced dose CBCT and kV image pair, respectively. Rotational shifts were within 0.2 degree and 0.7 degrees for all sites, for the reduced dose CBCTs and kV image pair, respectively.ConclusionFor bony anatomy‐based image guidance, CBCT dose can be reduced to a value similar to that of a kV image pair with similar or better patient positioning accuracy than kV image pair alignment. Where rotations are important to correct, CBCT will be superior to orthogonal kV imaging without significantly increased imaging dose. This is especially important for image guidance for pediatric patient treatments.

Twin robotic x-ray system in small bone and joint trauma: impact of cone-beam computed tomography on treatment decisions

ObjectivesTrauma evaluation of extremities can be challenging in conventional radiography. A multi-use x-ray system with cone-beam CT (CBCT) option facilitates ancillary 3-D imaging without repositioning. We assessed the clinical value of CBCT scans by analyzing the influence of additional findings on therapy.MethodsNinety-two patients underwent radiography and subsequent CBCT imaging with the twin robotic scanner (76 wrist/hand/finger and 16 ankle/foot/toe trauma scans). Reports by on-call radiologists before and after CBCT were compared regarding fracture detection, joint affliction, comminuted injuries, and diagnostic confidence. An orthopedic surgeon recommended therapy based on reported findings. Surgical reports (N = 52) and clinical follow-up (N = 85) were used as reference standard.ResultsCBCT detected more fractures (83/64 of 85), joint involvements (69/53 of 71), and multi-fragment situations (68/50 of 70) than radiography (all p < 0.001). Six fractures suspected in radiographs were ruled out by CBCT. Treatment changes based on additional information from CBCT were recommended in 29 patients (31.5%). While agreement between advised therapy before CBCT and actual treatment was moderate (κ = 0.41 [95% confidence interval 0.35–0.47]; p < 0.001), agreement after CBCT was almost perfect (κ = 0.88 [0.83–0.93]; p < 0.001). Diagnostic confidence increased considerably for CBCT studies (p < 0.001). Median effective dose for CBCT was 4.3 μSv [3.3–5.3 μSv] compared to 0.2 μSv [0.1–0.2 μSv] for radiography.ConclusionsCBCT provides advantages for the evaluation of acute small bone and joint trauma by detecting and excluding extremity fractures and fracture-related findings more reliably than radiographs. Additional findings induced therapy change in one third of patients, suggesting substantial clinical impact.Key Points• With cone-beam CT, extremity fractures and fracture-related findings can be detected and ruled out more reliably than with conventional radiography.• Additional diagnostic information provided by cone-beam CT scans has substantial impact on therapy in small bone and joint trauma.• For distal extremity injury assessment, one-stop-shop imaging without repositioning is feasible with the twin robotic x-ray system.

A review of dental cone-beam CT dose conversion coefficients.

The purpose of this study was to review the literature to examine the usage and magnitude of effective dose conversion factors (DCE) for dental cone beam CT (CBCT) scanners. A PubMed literature search for publications relating to radiation dosimetry in dental radiography was performed. Papers were included if they reported DCE, or reported ICRP 103 effective dose and dose-area product. 71 papers relating to dental CBCT dosimetry were found, of which eight reported effective dose conversion factors or provided enough information to calculate dose conversion factors. Scanner model, effective dose, dose-area product, tube voltage, field of view size and DCE were extracted from the papers for analysis. DCE values ranged from 0.035 to 0.31 µSv/mGy-cm2 with a mean of 0.129 µSv/mGy-cm2 (SD = 0.056). When categorized into small (<100 cm2), medium (100-225 cm2) and large (>225 cm2) fields of view (FOV), linear fits to the effective dose and dose-area product yielded slopes of 0.129, 0.111 and 0.074 µSv/mGy-cm2 for small, medium and large FOVs respectively. The range of reported DCE values and spread with respect to field of view category suggests that DCE values that depend on FOV would provide more accurate effective dose estimates. Tube voltage was found to be a smaller factor in determining DCE. Reasonable values for DCE taking into account FOV size were obtained. There is considerable room for more work to be done to examine the behaviour of DCE with changes to patient age and dental CBCT imaging parameters.