Artifact-free CT images for electron beam therapy using a patient-specific non metallic shield

Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts. Furthermore, the treatment planning system (TPS) has a limitation on accurate dose calculations for high density materials. In this study, a Monte Carlo (MC)-based method was developed to accurately evaluate the dosimetric effect of the metallic shield. Two patients with a commercial tungsten shield of lens and two patients with a custom-made lead shield of lip were chosen to produce their non-metallic dummy shields using 3D scanner and printer. With these dummy shields, we generated artifact-free CT images. The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations with real material information were carried out. In addition, clinically relevant dose-volumetric parameters were calculated for the comparison between MC and TPS. Relative dosimetry was performed using radiochromic films. The dose reductions below metallic structures were shown on MC dose distributions, but not evident on TPS dose distributions. The differences in dose-volumetric parameters of PTV between TPS and MC for eye shield cases were not clearly shown. However, the mean dose of lens from TPS and MC was different. The MC results were in superior agreement with measured data in relative dosimetry. The lens dose could be overestimated by TPS. The differences in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip cases than in eye cases. The developed method is useful in predicting the realistic dose distributions around the organs blocked by the metallic shields.     

Occupational radiation exposure in vascular interventional radiology: A complete evaluation of different body regions

PurposeTo perform a complete evaluation on radiation doses, received by primary and assistant medical staff, while performing different vascular interventional radiology procedures.Materials and methodsWe evaluated dose received in different body regions during three categories of vascular procedures: lower limb angiography (Angiography), lower limb percutaneous transluminal angioplasty (Angioplasty) and stent graft placement for abdominal aortic aneurysm treatment (A. A. A. Treatment). We positioned the dosimeters near the eye lens, thyroid, chest, abdomen, hands, and feet of the interventional physicians. Equivalent dose was compared with annual dose limits for workers in order to determine the maximum number of procedures per year that each physician could perform. We assessed 90 procedures.ResultsWe found the highest equivalent doses in the A. A. A. Treatment, in which 90% of the evaluations indicated at least one region receiving more than 1 mSv per procedure. Angioplasty was the only procedural modality that provided statistically different doses for different professionals, which is an important aspect on regards to radiological protection strategies. In comparison with the dose limits, the most critical region in all procedures was the eye lens.ConclusionsSince each body region of the interventionist is exposed to different radiation levels, dose distribution measurements are essential for radiological protection strategies. These results indicate that dosimeters placed in abdomen instead of chest may represent more accurately the whole body doses received by the medical staff. Additional dosimeters and a stationary shield for the eye lens are strongly recommended.     

Mobile shielding evaluation on the fetal dose during a breast radiotherapy using Monte Carlo simulation

PurposeEvaluation of the out-of-field dose is an important aspect in radiotherapy. Due to the fetus radiosensitivity, this evaluation becomes even more conclusive when the patient is pregnant. In this work, a linear accelerator Varian Clinac 2100c operating at 6 MV, a pregnant anthropomorphic phantom (Maria), and different shields added above the abdominal region of the phantom were used for the analysis based on MCNPX. Methods: The simulations were performed for the medial and lateral projections, using either an open field collimation (10×16 cm²) or a multileaf collimator. The added shields (M1 and M2) were designed based on models proposed by Stovall et al. [1], intending to reduce the deposited dose on the fetus and related structures. Results: The presence of the shields showed to be effective in reducing the doses on the fetus, amniotic sac, and placenta, for example. A reduction of about 43% was found in the dose on the fetus when M2 was added, using the open field collimation, in comparison with the situation with no shield, being the lateral projection the main responsible for the dose. The use of MLC significatively reduced the doses in different structures, including on the fetus and amniotic sac, for example, in comparison to the open field situation. A slight increment on the dose in organs such as the eyes, thyroid and brain was found in both collimation systems, due to the presence of the shields. The contribution of the leakage radiation from the tube head of the linear accelerator was found to be in the order of µGy, being reduced by the presence of the M2 shield. Conclusion: Using the shields showed to be an essential feature in order to reduce the dose not only on the fetus, but also in important structures responsible to its development.     

Absorbed dose and image quality of Varian TrueBeam CBCT compared with OBI CBCT

Purpose: Nowadays, patient positioning and target localization can be verified by using kilovolt cone beam computed tomography (kV-CBCT). There have been various studies on the absorbed doses and image qualities of different kV-CBCT systems. However, the Varian TrueBeam CBCT (TB CBCT) system has not been investigated so far. We assess the image quality and absorbed dose of TB CBCT through comparison with those of on-board imager (OBI) CBCT.Methods: The image quality was evaluated using two phantoms. A CATPHAN phantom measured the image quality parameters of the American Association of Physicists in Medicine Task Group 142 (AAPM TG-142) report. These factors are the pixel value stability and accuracy, noise, high-contrast resolution, low-contrast resolution, and image uniformity. A H₂SO₄ phantom was used to evaluate the image uniformity over a larger region than the CATPHAN phantom. In evaluating the absorbed dose, the radial dose profile and the patient organ doses at the prostate and rectum levels were evaluated.Results: The image quality parameters of AAPM TG-142 using TB CBCT are equal to or greater than those of OBI CBCT. In particular, the contrast-to-noise ratio with TB CBCT is 2.5 times higher than that with OBI CBCT. For the test of a large field uniformity, the maximum difference in the Hounsfield unit (HU) values between the centre and peripheral regions is within 30 HU with TB CBCT and 283 HU with OBI CBCT. The maximum absorbed dose with TB CBCT is decreased by 60%.Conclusions: We find that the image quality improved and the absorbed dose decreased with TB CBCT in comparison to those with OBI CBCT. Its image uniformity is also superior over a larger scanning range.     

Enhancement of soft-tissue contrast in cone-beam CT using an anti-scatter grid with a sparse sampling approach

PurposeAnti-scatter grids suppress the scatter substantially thus improving image contrast in radiography. However, its active use in cone-beam CT for the purpose of improving contrast-to-noise ratio (CNR) has not been successful mainly due to the increased noise related to Poisson statistics of photons. This paper proposes a sparse-view scanning approach to address the above issue.MethodCompared to the conventional cone-beam CT imaging framework, the proposed method reduces the number of projections and increases exposure in each projection to enhance image quality without an additional cost of radiation dose to patients. For image reconstruction from sparse-view data, an adaptive-steepest-descent projection-onto-convex-sets (ASD POCS) algorithm regularized by total-variation (TV) minimization was adopted. Contrast and CNR with various scattering conditions were evaluated in projection domain by a simulation study using GATE. Then we evaluated contrast, resolution, and image uniformity in CT image domain with Catphan phantom. A head phantom with soft-tissue structures was also employed for demonstrating a realistic application. A virtual grid-based estimation and reduction of scatter has also been implemented for comparison with the real anti-scatter grid.ResultsIn the projection domain evaluation, contrast and CNR enhancement was observed when using an anti-scatter grid compared to the virtual grid. In the CT image domain, the proposed method produced substantially higher contrast and CNR of the low-contrast structures with much improved image uniformity.ConclusionWe have shown that the proposed method can provide high-quality CBCT images particularly with an increased contrast of soft-tissue at a neutral dose for image-guidance.     

The influence of operator position,height and body orientation on eye lens dose in interventional radiology and cardiology: Monte Carlo simulations versus realistic clinical measurements

ObjectiveThis paper aims to provide some practical recommendations to reduce eye lens dose for workers exposed to X-rays in interventional cardiology and radiology and also to propose an eye lens correction factor when lead glasses are used.MethodsMonte Carlo simulations are used to study the variation of eye lens exposure with operator position, height and body orientation with respect to the patient and the X-ray tube. The paper also looks into the efficiency of wraparound lead glasses using simulations. Computation results are compared with experimental measurements performed in Spanish hospitals using eye lens dosemeters as well as with data from available literature.ResultsSimulations showed that left eye exposure is generally higher than the right eye, when the operator stands on the right side of the patient. Operator height can induce a strong dose decrease by up to a factor of 2 for the left eye for 10-cm-taller operators. Body rotation of the operator away from the tube by 45°–60° reduces eye exposure by a factor of 2. The calculation-based correction factor of 0.3 for wraparound type lead glasses was found to agree reasonably well with experimental data.ConclusionsSimple precautions, such as the positioning of the image screen away from the X-ray source, lead to a significant reduction of the eye lens dose. Measurements and simulations performed in this work also show that a general eye lens correction factor of 0.5 can be used when lead glasses are worn regardless of operator position, height and body orientation.     

Evaluation of patient organ doses from kilovoltage cone-beam CT imaging in radiation therapy

BackgroundCurrently, CBCT system is an indispensable component of radiation therapy units. Because of that, it is important in treatment planning and diagnosis. CBCT is also an crucial tool for patient positioning and verification in image-guided radiation therapy (IGRT). Therefore, it is critical to investigate the patient organ doses arising from CBCT imaging. The purpose of this study is to evaluate patient organ doses and effective dose to patients from three different protocols of Elekta Synergy XVI system for kV CBCT imaging examinations in image guided radiation therapy.Materials and methodsOrgan dose measurements were done with thermoluminescent dosimeters in Alderson RA NDO male phantom for head & neck (H&N), chest and pelvis protocols of the Elekta Synergy XVI kV CBCT system. From the measured organ dose, effective dose to patients were calculated according to the International Commission on Radiological Protection 103 report recommendations.ResultsFor H&N, chest and pelvis scans, the organ doses were in the range of 0.03–3.43 mGy, 6.04–22.94 mGy and 2.5–25.28 mGy, respectively. The calculated effective doses were 0.25 mSv, 5.56 mSv and 4.72 mSv, respectively.ConclusionThe obtained results were consistent with the most published studies in the literature. Although the doses to patient organs from the kV CBCT system were relatively low when compared with the prescribed treatment dose, the amount of delivered dose should be monitored and recorded carefully in order to avoid secondary cancer risk, especially in pediatric examinations.     

Eye lens dose correlations with personal dose equivalent and patient exposure in paediatric interventional cardiology performed with a fluoroscopic biplane system

PurposeTo analyse the correlations between the eye lens dose estimates performed with dosimeters placed next to the eyes of paediatric interventional cardiologists working with a biplane system, the personal dose equivalent measured on the thorax and the patient dose.MethodsThe eye lens dose was estimated in terms of H_p(0.07) on a monthly basis, placing optically stimulated luminescence dosimeters (OSLDs) on goggles. The H_p(0.07) personal dose equivalent was measured over aprons with whole-body OSLDs. Data on patient dose as recorded by the kerma-area product (P_KA) were collected using an automatic dose management system. The 2 paediatric cardiologists working in the facility were involved in the study, and 222 interventions in a 1-year period were evaluated. The ceiling-suspended screen was often disregarded during interventions.ResultsThe annual eye lens doses estimated on goggles were 4.13 ± 0.93 and 4.98 ± 1.28 mSv. Over the aprons, the doses obtained were 10.83 ± 0.99 and 11.97 ± 1.44 mSv. The correlation between the goggles and the apron dose was R² = 0.89, with a ratio of 0.38. The correlation with the patient dose was R² = 0.40, with a ratio of 1.79 μSv Gy⁻¹ cm⁻². The dose per procedure obtained over the aprons was 102 ± 16 μSv, and on goggles 40 ± 9 μSv. The eye lens dose normalized to P_KA was 2.21 ± 0.58 μSv Gy⁻¹ cm⁻².ConclusionsMeasurements of personal dose equivalent over the paediatric cardiologist’s apron are useful to estimate eye lens dose levels if no radiation protection devices are typically used.     

Dual-energy CT imaging of orbits during episcleral brachytherapy with Ru-106 plaques: A phantom study on its potential for plaque position verification

PurposeTo investigate the potential of dual energy CT (DECT) to suppress metal artifacts and accurately depict episcleral brachytherapy Ru-106 plaques after surgical placement.MethodsAn anthropomorphic phantom simulating the adult head after surgical placement of a Ru-106 plaque was employed. Nine DECT acquisition protocols for orbital imaging were applied. Monochromatic 140 keV images were generated using iterative reconstruction and an available metal artifact reduction algorithm. Generated image datasets were graded by four observers regarding the ability to accurate demarcate the Ru-106 plaque. Objective image quality and visual grading analysis (VGA) was performed to compare different acquisition protocols. The DECT imaging protocol which allowed accurate plaque demarcation at minimum exposure was identified. The eye-lens dose from orbital DECT, with and without the use of radioprotective bismuth eye-shields, was determined using Monte Carlo methods.ResultsAll DECT acquisition protocols were judged to allow clear demarcation of the plaque borders despite some moderate streaking/shading artifacts. The differences between mean observers’ VGA scores for the 9 DECT imaging protocols were not statistically significant (p > 0.05). The eye-lens dose from the proposed low-exposure DECT protocol was found to be 20.1 and 22.8 mGy for the treated and the healthy eye, respectively. Bismuth shielding was found to accomplish >40% reduction in eye-lens dose without inducing shielding-related artifacts that obscure plaque delineation.ConclusionsDECT imaging of orbits after Ru-106 plaque positioning for ocular brachytherapy was found to allow artifact-free delineation of plaque margins at relatively low patient exposure, providing the potential for post-surgery plaque position verification.     

Characterization of Scattered X-Ray Photons in Dental Cone-Beam Computed Tomography

Purpose

Scatter is a very important artifact causing factor in dental cone-beam CT (CBCT), which has a major influence on the detectability of details within images. This work aimed to improve the image quality of dental CBCT through scatter correction.

Methods

Scatter was estimated in the projection domain from the low frequency component of the difference between the raw CBCT projection and the projection obtained by extrapolating the model fitted to the raw projections acquired with 2 different sizes of axial field-of-view (FOV). The function for curve fitting was optimized by using Monte Carlo simulation. To validate the proposed method, an anthropomorphic phantom and a water-filled cylindrical phantom with rod inserts simulating different tissue materials were scanned using 120 kVp, 5 mA and 9-second scanning time covering an axial FOV of 4 cm and 13 cm. The detectability of the CT image was evaluated by calculating the contrast-to-noise ratio (CNR).

Results

Beam hardening and cupping artifacts were observed in CBCT images without scatter correction, especially in those acquired with 13 cm FOV. These artifacts were reduced in CBCT images corrected by the proposed method, demonstrating its efficacy on scatter correction. After scatter correction, the image quality of CBCT was improved in terms of target detectability which was quantified as the CNR for rod inserts in the cylindrical phantom.

Conclusions

Hopefully the calculations performed in this work can provide a route to reach a high level of diagnostic image quality for CBCT imaging used in oral and maxillofacial structures whilst ensuring patient dose as low as reasonably achievable, which may ultimately make CBCT scan a reliable and safe tool in clinical practice.     

A review of dose calculation approaches with cone beam CT in photon and proton therapy

Background and purposeThe use of cone beam computed tomography (CBCT) for performing dose calculations in radiation therapy has been widely investigated as it could provide a quantitative analysis of the dosimetric impact of changes in patients during the treatment. The aim of this review was to classify different techniques adopted to perform CBCT dose calculation and to report their dosimetric accuracy with respect to the metrics used.Methods and materialsA literature search was carried out in PubMed and ScienceDirect databases, based upon the following keywords: “cone beam computed tomography”, “CBCT”, “cone beam CT”, “dose calculation”, “accuracy”. Sixty-nine peer-reviewed relevant articles were included in this review: thirty-one patient studies, fifteen phantom studies and twenty-three patient & phantom studies. Most studies were found to have focused on head and neck, lung and prostate cancers.ResultsThe techniques adopted to perform CBCT dose calculation have been grouped in six categories labelled as (1) pCT calibration, (2) CBCT calibration, (3) HU override, (4) Deformable image registration, (5) Dose deformation, and (6) Combined techniques. Differences between CBCT dose and reference dose were reported both for target volumes and OARs.ConclusionsA comparison among the available techniques for CBCT dose calculations is challenging as many variables are involved. Therefore, a set of reporting standards is recommended to enable meaningful comparisons among different studies. The accuracy of the results was strongly dependent on the image quality, regardless of the methods used, highlighting the need for dose validation and quality assurance standards.     

Precision IORT – Image guided intraoperative radiation therapy (igIORT) using online treatment planning including tissue heterogeneity correction

BackgroundTo the present date, IORT has been eye and hand guided without treatment planning and tissue heterogeneity correction. This limits the precision of the application and the precise documentation of the location and the deposited dose in the tissue. Here we present a set-up where we use image guidance by intraoperative cone beam computed tomography (CBCT) for precise online Monte Carlo treatment planning including tissue heterogeneity correction.Materials and methodsAn IORT was performed during balloon kyphoplasty using a dedicated Needle Applicator. An intraoperative CBCT was registered with a pre-op CT. Treatment planning was performed in Radiance using a hybrid Monte Carlo algorithm simulating dose in homogeneous (MCwater) and heterogeneous medium (MChet). Dose distributions on CBCT and pre-op CT were compared with each other. Spinal cord and the metastasis doses were evaluated.ResultsThe MCwater calculations showed a spherical dose distribution as expected. The minimum target dose for the MChet simulations on pre-op CT was increased by 40% while the maximum spinal cord dose was decreased by 35%. Due to the artefacts on the CBCT the comparison between MChet simulations on CBCT and pre-op CT showed differences up to 50% in dose.ConclusionsigIORT and online treatment planning improves the accuracy of IORT. However, the current set-up is limited by CT artefacts. Fusing an intraoperative CBCT with a pre-op CT allows the combination of an accurate dose calculation with the knowledge of the correct source/applicator position. This method can be also used for pre-operative treatment planning followed by image guided surgery.     

Dose calculation accuracy of different image value to density tables for cone-beam CT planning in head & neck and pelvic localizations

PurposeWe aimed to identify the most accurate combination of phantom and protocol for image value to density table (IVDT) on volume-modulated arc therapy (VMAT) dose calculation based on kV-Cone-beam CT imaging, for head and neck (H&N) and pelvic localizations.MethodsThree phantoms (Catphan^®600, CIRS^®062M (inner phantom for head and outer phantom for body), and TomoTherapy^® “Cheese” phantom) were used to create IVDT curves of CBCT systems with two different CBCT protocols (Standard-dose Head and Standard Pelvis). Hounsfield Unit (HU) time stability and repeatability for a single On-Board-Imager (OBI) and compatibility of two distinct devices were assessed with Catphan^®600. Images from the anthropomorphic phantom CIRS ATOM^® for both CT and CBCT modalities were used for VMAT dose calculation from different IVDT curves. Dosimetric indices from CT and CBCT imaging were compared.ResultsIVDT curves from CBCT images were highly different depending on phantom used (up to 1000 HU for high densities) and protocol applied (up to 200 HU for high densities). HU time stability was verified over seven weeks. A maximum difference of 3% on the dose calculation indices studied was found between CT and CBCT VMAT dose calculation across the two localizations using appropriate IVDT curves. One IVDT curve per localization can be established with a bi-monthly verification of IVDT-CBCT.ConclusionsThe IVDT-CBCT_CIRS-Head phantom with the Standard-dose Head protocol was the most accurate combination for dose calculation on H&N CBCT images. For pelvic localizations, the IVDT-CBCT_Cheese established with the Standard Pelvis protocol provided the best accuracy.     

A new cone-beam computed tomography dosimetry method providing optimal measurement positions: A Monte Carlo study

PurposeThe conventional weighted computed tomography dose index (CTDI_w) may not be suitable for cone-beam computed tomography (CBCT) dosimetry because a cross-sectional dose distribution is angularly inhomogeneous owing to partial angle irradiations. This study was conducted to develop a new dose metric (f(0)^CB_w) for CBCT dosimetry to determine a more accurate average dose in the central cross-sectional plane of a cylindrical phantom using Monte Carlo simulations.MethodsFirst, cross-sectional dose distributions of cylindrical polymethyl methacrylate phantoms over a wide range of phantom diameters (8–40 cm) were calculated for various CBCT scan protocols. Then, by obtaining linear least-squares fits of the full datasets of the cross-sectional dose distributions, the optimal radial positions, which represented measurement positions for the average phantom dose, were determined. Finally, the f(0)^CB_w method was developed by averaging point doses at the optimal radial positions of the phantoms. To demonstrate its validity, the relative differences between the average doses and each dose index value were estimated for the devised f(0)^CB_w, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ResultsThe relative differences between the average doses and each dose index value were within 4.1%, 16.7%, and 11.9% for the devised, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ConclusionsThe devised f(0)^CB_w value was calculated by averaging four “point doses” at 90° intervals and the optimal radial positions of the cylindrical phantom. The devised method can estimate the average dose more accurately than the previously developed CTDI_w methods for CBCT dosimetry.     

Monte Carlo simulation of eye lens dose reduction from CT scan using organ based tube current modulation

PurposeTo investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method.MethodsTo calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10° for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used.ResultsDose differences between two eye models were less than 20%, but large variations were observed among dose results from different projections of all tube voltages investigated. Dose results from 0° (AP) directions were 60 times greater than those from 180° (PA) directions, which enables organ based TCM reduce lens doses by more than 47%.ConclusionsOrgan based TCM may be used to reduce lens doses. Stylized eye models are more anatomically realistic compared with voxelized eye models and are more reliable for dose evaluation.     

Automatic exposure control at single- and dual-heartbeat CTCA on a 320-MDCT volume scanner: Effect of heart rate,exposure phase window setting,and reconstruction algorithm

PurposeTo investigate whether electrocardiogram (ECG)-gated single- and dual-heartbeat computed tomography coronary angiography (CTCA) with automatic exposure control (AEC) yields images with uniform image noise at reduced radiation doses.Materials and methodsUsing an anthropomorphic chest CT phantom we performed prospectively ECG-gated single- and dual-heartbeat CTCA on a second-generation 320-multidetector CT volume scanner. The exposure phase window was set at 75%, 70–80%, 40–80%, and 0–100% and the heart rate at 60 or 80 or corr80 bpm; images were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR, adaptive iterative dose reduction 3D). We applied AEC and set the image noise level to 20 or 25 HU. For each technique we determined the image noise and the radiation dose to the phantom center.ResultsWith half-scan reconstruction at 60 bpm, a 70–80% phase window- and a 20-HU standard deviation (SD) setting, the imagenoise level and -variation along the z axis manifested similar curves with FBP and IR. With half-scan reconstruction, the radiation dose to the phantom center with 70–80% phase window was 18.89 and 12.34 mGy for FBP and 4.61 and 3.10 mGy for IR at an SD setting SD of 20 and 25 HU, respectively. At 80 bpm with two-segment reconstruction the dose was approximately twice that of 60 bpm at both SD settings. However, increasing radiation dose at corr80 bpm was suppressed to 1.39 times compared to 60 bpm.ConclusionAEC at ECG-gated single- and dual-heartbeat CTCA controls the image noise at different radiation dose.     

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

PurposeTo 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®.MethodsThe 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 (K_i) at the center of the CBCT field-of-view and K_i 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.ResultsThe experimental ED estimate for the low-dose 3D-modes was 2.41 and 0.35 mSv with O-arm®O2 (Low Dose 3D-small-abdomen) and Surgivisio® (3DSU-91 images), respectively. PCXMC results were consistent: 1.54 and 0.30 mSv. Organ doses were 5 to 12 times lower with Surgivisio®. K_i at patient skin were comparable on lateral 2D-imaging (0.5 mGy), but lower with O-arm®O2 on anteroposterior (0.3 versus 0.9 mGy). Both systems show poor low contrast resolution and similar high contrast spatial resolution (7 line-pairs/cm).ConclusionsThis 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.     

Posterior kV-CBCT scanning of the head and neck region minimizes doses to critical organs with sustained image quality

We evaluated the absorbed dose to critical organs, as well as the image quality, at different partial angles in kV-CBCT (Cone Beam Computed Tomography) scanning of the head and neck region. CBCT images of phantom from a 200° rotation were performed by using three different scanning paths, anterior, posterior, and right lateral with Catphan504 and RANDO phantoms. Critical organ dose was measured using TLD 100H in the RANDO phantom. The image quality of those phantoms was evaluated, using HU uniformity, HU linearity, contrast-to-noise ratio, low contrast visibility and spatial resolution with the Catphan504 dataset; and 5-point grading scales for the RANDO phantom dataset by five radiation oncologists. The image qualities from Catphan504 and RANDO phantom of every scanning path were comparable, with no statistically significant difference (p ≥ 0.05). However, there was a significant difference in the critical organ dose in all paths (p < 0.05), depending on the critical organ location and the scanning direction. Scanning directions show no effects on the image quality. Differences in absorbed dose to critical organs should were evaluated. The posterior scanning path for the CBCT was deemed preferable due because of considerably lower doses to several critical organs of the head and neck region.     

Two examples of indication specific radiation dose calculations in dental CBCT and Multidetector CT scanners

PurposeTo calculate organ doses and estimate the effective dose for justification purposes in patients undergoing orthognathic treatment planning purposes and temporal bone imaging in dental cone beam CT (CBCT) and Multidetector CT (MDCT) scanners.MethodsThe radiation dose to the ICRP reference male voxel phantom was calculated for dedicated orthognathic treatment planning acquisitions via Monte Carlo simulations in two dental CBCT scanners, Promax 3D Max (Planmeca, FI) and NewTom VGi evo (QR s.r.l, IT) and in Somatom Definition Flash (Siemens, DE) MDCT scanner. For temporal bone imaging, radiation doses were calculated via MC simulations for a CBCT protocol in NewTom 5G (QR s.r.l, IT) and with the use of a software tool (CT-expo) for Somatom Force (Siemens, DE). All procedures had been optimized at the acceptance tests of the devices.ResultsFor orthognathic protocols, dental CBCT scanners deliver lower doses compared to MDCT scanners. The estimated effective dose (ED) was 0.32 mSv for a normal resolution operation mode in Promax 3D Max, 0.27 mSv in VGi-evo and 1.18 mSv in the Somatom Definition Flash. For temporal bone protocols, the Somatom Force resulted in an estimated ED of 0.28 mSv while for NewTom 5G the ED was 0.31 and 0.22 mSv for monolateral and bilateral imaging respectively.ConclusionsTwo clinical exams which are carried out with both a CBCT or a MDCT scanner were compared in terms of radiation dose. Dental CBCT scanners deliver lower doses for orthognathic patients whereas for temporal bone procedures the doses were similar.     

A multicenter study of radiation doses to the eye lenses of medical staff performing non-vascular imaging and interventional radiology procedures in Japan

PurposeThis study aimed to measure the eye lens doses received by physicians and other medical staff participating in non-vascular imaging and interventional radiology procedures in Japan.Material and methodsFrom October 2014 to March 2017, 34 physicians and 29 other medical staff engaged in non-vascular imaging and interventional radiology procedures at 18 Japanese medical facilities. These professionals wore radioprotective lead glasses equipped with small, optically stimulated luminescence dosimeters and additional personal dosimeters at the neck during a 1-month monitoring period. The H_p(3) and the H_p(10) and H_p(0.07) were obtained from these devices, respectively. The monthly H_p(3), H_p(10), and H_p(0.07) for each physician and other medical staff member were then rescaled to a 12-month period to enable comparisons with the revised occupational equivalent dose limit for the eye lens.ResultsAmong physicians, the average annual H_p(3) values measured by the small luminescence dosimeters on radioprotective glasses were 25.5 ± 38.3 mSv/y (range: 0.4–166.8 mSv/y) and 9.3 ± 16.6 mSv/y (range: 0.3–82.4 mSv/y) on the left and right sides, respectively. The corresponding values for other medical staff were 3.7 ± 3.1 mSv/y (range: 0.4–10.4 mSv/y) and 3.2 ± 2.7 mSv/y (range: 0.5–11.5 mSv/y), respectively.ConclusionsThe eye lens doses incurred by physicians and other medical staff who engaged in non-vascular imaging and interventional radiology procedures in Japan were provided. Physicians should wear radioprotective glasses and use additional radioprotective devices to reduce the amount of eye lens doses they receive.