Comparison of absorbed doses and organ doses measured with thermoluminescent dosimeters and Gafchromic film for cone beam computed tomography examination of the posterior mandibular region in a head phantom.

OBJECTIVES: We aimed to map the correlation between thermoluminescent dosimeters (TLDs) and Gafchromic film for measuring absorbed doses and to compare minimum, maximum, and mean absorbed doses over larger regions of interest and at various craniofacial organs and tissues during cone beam computed tomography (CBCT) exposure of the mandibular third molar region. STUDY DESIGN: We positioned TLDs at 75 measurement points in a head phantom. Gafchromic film was cut to the same shape as the 5 levels of the phantom and was placed on top of the TLDs. Both dosimetry methods thus included the surface of each level simultaneously. CBCT scans were made using a 5 × 5 cm field of view and a rotation angle of 200°. Measurements included absorbed dose distributions, doses at all 75 points, and minimum, maximum, and mean doses within organs and tissues. RESULTS: The correlation of point-dose measurements at all TLD sites with doses measured on film was strong (R2 = 0.9687), with greatest correlation at lower doses (<2 mGy). Large deviations between TLD and film measurements of minimum and maximum doses and absorbed doses to the organs occurred at all 5 levels. TLD positioning failed to cover several organ sites; for these, only absorbed dose measurements from the film were available. CONCLUSIONS: TLDs were unable to sample dose distributions and gradients accurately. The characteristics of Gafchromic LD-V1 film make it a favorable alternative in dental CBCT dosimetry.

Image quality assessment of low-dose protocols in cone beam computed tomography of the anterior maxilla.

OBJECTIVES: To evaluate overall image quality and visibility of anatomic structures on low-dose cone beam computed tomography (CBCT) scans and the effect of a noise reduction filter for assessment of the anterior maxilla. METHODS: We obtained 48 CBCT volumes on 8 skull-phantoms using 6 protocols: 2 clinical default protocols [standard definition (SD) and high definition (HD)] and 4 low-dose protocols, 2 with a noise reduction filter [ultra-low-dose with high definition (ULDHD) and ultra-low-dose (ULD)] and 2 without [low-dose with high definition (LDHD) and low-dose (LD)]. Overall image quality and visibility of 8 anatomic structures were assessed by 5 observers and statistically analyzed using the Wilcoxon signed rank test. Intra- and interobserver agreement was measured using Cohen's weighted kappa. RESULTS: HD provided higher overall image quality than diagnostically required; LD scored lower than diagnostically acceptable. ULDHD, ULD, and LDHD were acceptable. For anatomic structures, ULDHD and ULD were acceptable. LDHD and LD showed significantly inferior visibility for 1 and 4 structures, respectively. Mean values of intra- and interobserver agreement were 0.395 to 0.547 and 0.350 to 0.370, respectively. CONCLUSIONS: ULDHD, ULD, and LDHD may be recommended for assessment of impacted maxillary canines. The noise reduction filter affects image quality positively only at low exposure.

Bimodal ERCP, a new way of seeing things.

Background and study aims Conventional endoscopic retrograde cholangiopancreatography (ERCP) is hampered by two-dimensional visualization, post-procedural adverse events (AEs), and exposure to ionizing radiation. Bimodal ERCP might mitigate these challenges, but no reports of its use are available to date. The aim of this study was to explore the feasibility of bimodal ERCP, while investigating its potential clinical yield. Patients and methods This was a retrospective observational study of patients that underwent bimodal ERCP in a single tertiary academic referral center. Thirteen patients undergoing conventional ERCP had a previously T2-weighted isotropic 3 D TSE MRCP sequence aligned and fused with the two-dimensional image generated from the fluoroscopy c-arm unit in real time. Results Over a 2-month period, 13 patients with a mean age of 54 underwent bimodal ERCP for bile duct stricture (61.5 %), complex cholelithiasis (7.7 %) and ductal leakage (30.1 %). Bimodal ERCP was feasible in all 13 cases, and image quality was assessed as "good" in 11 patients (84.6 %). Bimodal ERCP aided in visualizing the lesion of interest (76.9 %), assisted in understanding the 3 D anatomy of the biliopancreatic ductal system (61.5 %), and aided in finding a favorable position for the c-arm (38.4 %) for subsequent therapeutic intervention. Conclusions This first report on bimodal ERCP proves its feasibility and suggests that it may assist in increasing both the diagnostic and therapeutic yield of ERCP, while at the same time decreasing AEs during and after ERCP. Its main application might lie in treatment of complex intrahepatic disease.

Radiation dose in cone beam CT guided ERCP.

PURPOSE: To evaluate the practical and radiation safety considerations in utilization of 3-D imaging through cone beam computed tomography (CBCT) in endoscopic retrograde cholangiopancreatography (ERCP). METHOD: ERCP procedures were performed using an Artis Q interventional suite (Siemens Healthineers), including 42 procedures with CBCT. Some CBCT cases used the standard "DR" exposure protocol and some used the low dose protocol "DR care". Data on x-ray radiation doses were retrospectively collected and to help optimize technical factors surrounding the procedure and compared to radiation exposure data of patients undergoing conventional ERCP. RESULTS: The median dose area product was 24.4 Gycm2 for one DR volume and 5.07 Gycm2 for one DR care volume. The median total dose area product was 6.52 Gycm2 for conventional ERCP, 48.9 Gycm2 for procedures using DR and 19.7 Gycm2 when using DR care. Conventional ERCP resulted in a significantly lower radiation dose than procedures using either CBCT protocols (p < 0.001). However, conventional ERCP showed a large number of outliers with higher dose at the level of, or surpassing, CBCT procedures. CONCLUSIONS: For less complex procedures with small x-ray doses and short fluoroscopy times conventional 2-D x-ray technique is clinically sufficient and utilizes less radiation dose than CBCT methods, but there is a wide range of doses and extreme outliers have been observed. CBCT can facilitate ERCP in cases with difficult ducal anatomy, possibly reducing procedural time, x-ray exposure time and need for contrast injections. Methods for prediction on high radiation ERCPs are needed to standardize and optimize patient selection for CBCT-ERCP.

Effective dose reduction using collimation function in digital panoramic radiography and possible clinical implications in dentistry.

OBJECTIVES:: The primary aim was to evaluate the effective dose for a full size panoramic image and nine different panoramic protocols using collimation. The secondary aim was to estimate possible reduction of effective dose in clinical situations. METHODS: Effective dose, according to International Commission on Radiological Protection 2007 was determined for a full size panoramic image and nine different panoramic protocols applying collimation on an anthropomorphic Rando phantom, using metal-oxide semiconductor field-effect transistor dosemeters. The collimation protocols were chosen based on common diagnostic questions. 10 exposures were made for each protocol using a Planmeca ProMax® 2D (Helsinki, Finland). The mean effective doses were calculated according to clinical default exposure settings and compared for all protocols. A retrospective analysis of 252 referrals to a specialist clinic in dentomaxillofacial radiology assessed usability and dose reduction applying nine different collimation protocols, based on possible collimation of panoramic images. Dose reduction was calculated applying collimation feature in comparison to constant use of full size panoramic imaging. Referrals were categorized according to indication for radiographic examination. RESULTS:: Effective dose of a full size panoramic radiograph was 17.6 µSv at 8 mA and 66 kV. The dose reduction for the collimated images compared to a full size panoramic radiograph ranged from 4.5 to 86.9%. Potential total dose reduction in the studied sample was 35% if collimation feature had been applied. In four out of five of the referrals, collimation was possible and in 61% of the referrals the indication for radiographic examination was restricted to the dental alveolar region, reducing the dose by 40.3% compared with a full size panoramic image. CONCLUSIONS:: Since the effective dose may be reduced without losing diagnostic information in the area of interest, collimation feature of panoramic imaging should be routinely applied when the diagnostic task allows.

Radiation dose from X-ray examinations of impacted canines: cone beam CT vs two-dimensional imaging.

OBJECTIVES: To compare the radiation dose to children examined for impacted canines, using two-dimensional (2D) examinations (panoramic and periapical radiographs) and cone beam CT (CBCT). METHODS: Organ doses were determined using an anthropomorphic 10-year-old child phantom. Two CBCT devices, a ProMax3D and a NewTom5G, were examined using thermoluminescent dosimeters. For the panoramic radiograph, a Promax device was used and for periapical radiographs, a Prostyle device with a ProSensor digital sensor was used. Both the panoramic and the intraoral devices were examined using Gafchromic-QR2 dosimetric film placed between the phantom slices. RESULTS: ProMax3D and NewTom5G resulted in an effective dose of 88 µSv and 170 µSv respectively. A panoramic radiograph resulted in an effective dose of 4.1 µSv, while a periapical radiograph resulted in an effective dose of 0.6 µSv and 0.7 µSv using a maxillary lateral projection and central maxillary incisor projection respectively. CONCLUSIONS: The effective dose from CBCT ranged from 140 times higher dose (NewTom5G compared to two periapical radiographs) to 15 times higher dose (ProMax3D compared to three periapical and one panoramic radiograph) than a 2D examination.

Cone-beam computed tomography with ultra-low dose protocols for pre-implant radiographic assessment: An in vitro study.

PURPOSE: To evaluate the ultra-low dose scanning protocols of a newly developed CBCT for pre-implant radiographic assessment. MATERIALS AND METHODS: A total number of 32 CBCT scans were exposed at 90 kV using ProMax 3D's standard (GS) and three ultra-low dose scanning protocols: high, mid and low definition (UL-HD, UL-MD and UL-LD) on eight human dry skulls with simulated soft tissue. The mAs values and the voxel size were 96mAs/200 µm, 28mAs/150 µm, 22.4mAs/200 µm and 7.5mAs/400 µm for scanning protocols GS, UL-HD, UL-MD and UL-LD, respectively. The overall image quality and the precision of anatomical landmarks were assessed on a 4-rank ordinal scale by seven observers. Logistic regression analysis and post-hoc Scheffé test were applied to analyse possible differences in image quality and recognition of the anatomical structures for the three ultra-low dose protocols, compared with the standard protocol. Additionally, observers performed bone quality assessment and bone quantity measurement at 96 predefined 2D cross-sectional images. A Pearson Chi-square test and a paired t-test were used to analyse assessed bone quality and quantity using the four scanning protocols respectively. RESULTS: For the CBCT unit, ProMax 3D, UL-LD was not diagnostically acceptable for pre-implant assessment, whereas the UL-HD and UL-MD were diagnostically acceptable regarding overall image quality, visibility of most anatomical structures and bone quality assessment. However, to recognise the border of mandibular canal and the border of maxillary sinus, standard protocol may be indicated for some cases. No statistically significant differences in bone height measurement were found when applying standard protocol and the three ultra-low dose protocols. CONCLUSIONS: Low-dose scanning protocols may be applied for pre-implant radiographic assessment, although image quality can be hampered if the radiation exposure is too low and the voxel size too large.

Assessment of the occupational eye lens dose for clinical staff in interventional radiology, cardiology and neuroradiology.

In accordance with recommendations by the International Commission on Radiological Protection, the current European Basic Safety Standards has adopted a reduced occupational eye lens dose limit of 20 mSv yr-1. The radiation safety implications of this dose limit is of concern for clinical staff that work with relatively high dose x-ray angiography and interventional radiology. Presented in this work is a thorough assessment of the occupational eye lens dose based on clinical measurements with active personal dosimeters worn by staff during various types of procedures in interventional radiology, cardiology and neuroradiology. Results are presented in terms of the estimated equivalent eye lens dose for various medical professions. In order to compare the risk of exceeding the regulatory annual eye lens dose limit for the widely different clinical situations investigated in this work, the different medical professions were separated into categories based on their distinct work pattern: staff that work (a) regularly beside the patient, (b) in proximity to the patient and (c) typically at a distance from the patient. The results demonstrate that the risk of exceeding the annual eye lens dose limit is of concern for staff category (a), i.e. mainly the primary radiologist/cardiologist. However, the results also demonstrate that the risk can be greatly mitigated if radiation protection shields are used in the clinical routine. The results presented in this work cover a wide range of clinical situations, and can be used as a first indication of the risk of exceeding the annual eye lens dose limit for staff at other medical centres.

Evaluation of the effective dose of cone beam computed tomography and multi-slice computed tomography for temporomandibular joint examinations at optimized exposure levels.

OBJECTIVES: To compare the effective dose to patients from temporomandibular joint examinations using a dental cone-beam CT device and a multi-slice CT device, both before and after dose optimization. METHODS: A Promax3D (Planmeca, Helsinki, Finland) dental cone-beam CT and a Lightspeed VCT (GE, Fairfield, USA) multi-slice CT were used. Organ doses and effective doses were estimated from thermoluminescent dosimeters at 61 positions inside an anthropomorphic phantom at the exposure settings in clinical use. Optimized exposure protocols were obtained through an optimization study using a dry skull phantom, where four observers rated image quality taken at different exposure levels. The optimal exposure level was obtained when all included criteria were rated as acceptable or better by all observers. RESULTS: The effective dose from a bilateral examination was 184 µSv for Promax3D and 113 µSv for Lightspeed VCT before optimization. Post optimization the bilateral effective dose was 92 µSv for Promax3D and 124 µSv for Lightspeed VCT. CONCLUSIONS: At optimized exposure levels, the effective dose from cone-beam CT was comparable to MSCT.

On the feasibility of utilizing active personal dosimeters worn on the chest to estimate occupational eye lens dose in x-ray angiography.

The International Commission on Radiological Protection (ICRP) has recommended that the occupational dose limit to the eye lens be substantially reduced. To ensure compliance with these recommendations, monitoring of the occupational eye lens dose is essential in certain hospital work environments. For assessment of the eye lens dose it is recommended to use a supplementary dosimeter placed at a position adjacent to the eye(s). Wearing a dosimeter at eye level can, however, be impractical and distributing and managing additional dosimeters over long periods of time is cumbersome and costly for large clinical sites. An attractive alternative is to utilize active personal dosimeters (APDs), which are routinely used by clinical staff for real-time monitoring of the personal dose equivalent rate (H(p)(10)). In this work, a formalism for the determination of eye lens dose from the response of such APD's worn on the chest is proposed and evaluated. The evaluation is based on both phantom and clinical measurements performed in an x-ray angiography suite for interventional cardiology. The main results show that the eye lens dose to the primary operator and to the assisting clinical staff can be conservatively estimated from the APD response as D(eye)(conductor) = 2.0 APD chest and D(eye)(assisting) = 1.0 APD chest, respectively. However, care should be exercised for particularly short assisting staff and if radiation protection shields are misused. These concerns can be greatly mitigated if the clinical staff are provided with adequate radiation protection training.

Effective radiation dose of a MSCT, two CBCT and one conventional radiography device in the ankle region.

BACKGROUND: The aim of this study was to assess and compare the effective doses (ICRP 103) in the ankle region of X-ray imaging resulting from a multi slice computed tomography (MSCT) device, two cone beam CT (CBCT) devices and one conventional x-ray device. METHODS: Organ dose measurements were performed using 20 metal oxide field effect transistor (MOSFET) dosimeters that were placed in a custom made anthropomorphic RANDO ankle phantom. The following scanners were assessed in this study: Siemens Sensation Open 24-slice MSCT-scanner (120 kVp, 54 mAs), NewTom 5G CBCT scanner (110 kVp, 2.3 - 59 mAs), Planmed Verity CBCT-scanner (90 kVp, 48 mAs), Shimadzu FH-21 HR direct radiography equipment (AP + LAT), (57 kVp, 16 mAs). RESULTS: Measurements of the MSCT device resulted in 21.4 µSv effective dose. The effective doses of CBCTs were between 1.9 µSv and 14.3 µSv for NewTom 5G and 6.0 µSv for Planmed Verity. Effective doses for the Shimadzu FH-21 HR conventional radiography were 1.0 µSv (LAT) and 0.5 µSv (AP), respectively. CONCLUSIONS: Compared with a conventional 2D radiographic device, this study showed a 14-fold effective dose for standard MSCT and 1.3 -10 fold effective dose for standard CBCT protocols. CBCT devices offers a 3D view of ankle imaging and exhibited lower effective doses compared with MSCT.

A practical approach to diode based in vivo dosimetry for intensity modulated radiotherapy.

A method for in vivo entrance dosimetry, using point detectors, in intensity modulated radiotherapy has been clinically evaluated. Diode dosimetry was performed for treatments of the head and neck and prostate regions. The results were good; 92.2% of the measurements showed deviations within ±5% of the expected values.