A practical method for routine eye lens dosimetry of staff in interventional radiology.

Hospital staff doing fluoroscopy-guided interventions receive the highest doses and are at risk of exceeding the new occupational eye lens dose limit of 20 mSv. Since the introduction of the new limit in the International Commission on Radiological Protection recommendations different eye lens dose monitoring techniques have been tested on phantoms. This study uses real-life dose data to assess the need for routine eye lens dose monitoring. The correlation of eye lens dose and Hp (10) measured with a whole-body dosemeter above the lead apron was investigated as an alternative to dedicated eye lens dosimetry. A survey taken among the medical personnel allowed to determine the preferred method for measuring eye lens doses in daily practice.

Radiosafe micro-computed tomography for longitudinal evaluation of murine disease models.

Implementation of in vivo high-resolution micro-computed tomography (µCT), a powerful tool for longitudinal analysis of murine lung disease models, is hampered by the lack of data on cumulative low-dose radiation effects on the investigated disease models. We aimed to measure radiation doses and effects of repeated µCT scans, to establish cumulative radiation levels and scan protocols without relevant toxicity. Lung metastasis, inflammation and fibrosis models and healthy mice were weekly scanned over one-month with µCT using high-resolution respiratory-gated 4D and expiration-weighted 3D protocols, comparing 5-times weekly scanned animals with controls. Radiation dose was measured by ionization chamber, optical fiberradioluminescence probe and thermoluminescent detectors in a mouse phantom. Dose effects were evaluated by in vivo µCT and bioluminescence imaging read-outs, gold standard endpoint evaluation and blood cell counts. Weekly exposure to 4D µCT, dose of 540-699 mGy/scan, did not alter lung metastatic load nor affected healthy mice. We found a disease-independent decrease in circulating blood platelets and lymphocytes after repeated 4D µCT. This effect was eliminated by optimizing a 3D protocol, reducing dose to 180-233 mGy/scan while maintaining equally high-quality images. We established µCT safety limits and protocols for weekly repeated whole-body acquisitions with proven safety for the overall health status, lung, disease process and host responses under investigation, including the radiosensitive blood cell compartment.

The growing concern of radiation dose in paediatric dental and maxillofacial CBCT: an easy guide for daily practice.

OBJECTIVES: To provide an indication-based and scanner-specific radiation dose and risk guide for paediatric patients undergoing dental and maxillofacial cone beam computed tomography (CBCT) examinations. METHODS: Five commercially available scanners were simulated in EGSnrc Monte Carlo (MC) code. Dedicated, in-house built, head and neck voxel models, each consisting of 22 segmented organs, were used in the study. Organ doses and life attributable risk (LAR) for cancer incidence were assessed for males and females, aged 5 to 14 years old, for every clinically available protocol: central upper and lower incisors, upper and lower premolars, upper and lower jaws, cleft palate, temporal bone, sinus, dentomaxillofacial complex, and face and skull imaging. Dose results were normalised to the x-ray tube load (mAs) and logarithmic curves were fit to organ dose and risk versus age data. RESULTS: Females demonstrated higher LAR values in all cases. A well-established dose decreasing pattern with increasing age-at-exposure was observed. Central upper incisor protocols were those with the lowest risk, contrary to skull protocols which provided the highest LAR values. Salivary glands and oral mucosa were the highest irradiated organs in all cases, followed by extrathoracic tissue (ET) in protocols where the entire nasal cavity was inside the primary field. The dose to thyroid was considerably high for younger patients. CONCLUSIONS: This work provides an extensive dose assessment guide for 5 dental CBCTs, enabling detailed dose assessment for every paediatric patient. KEY POINTS: • Radiation dose concerns due to the growing use of paediatric dental and maxillofacial CBCT underline the need for justification that should in part be based on radiation exposure in radiology. • Patient-specific dose calculations based on Monte Carlo simulations and head-neck paediatric voxel models overcome the limitations of conventional thermoluminescent dosimeter (TLD) dosimetry and provide proper guidance for justification of CBCT exposures. • Monte Carlo simulations with head-neck models reveal an organ dose and radiation risk decreasing pattern with increasing age at exposure, and with decreasing size of the scanning volume of interest (field of view).

Development and Validation of the Realistic Anthropomorphic Flexible (RAF) Phantom.

Voxel phantoms developed by segmenting computed tomography images are known to be more anatomically accurate than mathematical phantoms. However, due to their lack of flexibility and the complexity of voxel datasets, the use of voxel phantoms in dosimetry is often impractical. This paper describes the development of the realistic anthropomorphic flexible (RAF) polygonal mesh phantom, a novel phantom based on Boundary Representation (B-Rep) that merges anatomical accuracy and flexibility. Rather than using segmentation of tomography images, the modeling of the phantom's organs was based on freely and commercially available anatomical atlases, ICRP 89, and recent medical literature. To validate the phantom, a high-resolution voxel version was created for the MCNPx transport code. The voxelized RAF phantom was validated by comparing it with the ICRP 110 male phantom for external irradiations with parallel beams of photons and electrons. Dose coefficients obtained from simulations with the RAF phantom were compared with those from ICRP Publication 116. Relevant differences in organ doses were found.

Development of a paediatric head voxel model database for dosimetric applications.

OBJECTIVE: To develop a database of paediatric head voxel models intended for Monte Carlo (MC) dosimetric applications. METHODS: Seventeen head and neck CT image data sets were retrieved from the picture archiving and communicating system of our hospital and were reformed into voxel models. 22 organs were segmented at each data set. The segmented organ masses were compared to the respective age- and gender-specific ICRP reference mass value. Adjustments were made such that segmented and reference mass values coincide within a tolerance of 10%. A dental cone beam CT cleft palate simulation study was set up to demonstrate the applicability of our database to MC frameworks and to investigate the need for age- and gender-specific paediatric models. RESULTS: The designed database covers the age range from 2 months to 14 years old. Each model represents a reference head voxel phantom for its corresponding age and gender category. The simulation study revealed absorbed organ dose differences larger than 50% among the 5, 8 and 12 years old models when exposed to identical conditions. CONCLUSION: Children cannot be represented by one average phantom covering the entire age range like adults due to the fact that their organs change rapidly in size and shape. A database of paediatric head voxel models was designed to enable dose calculations via MC simulations. Advances in knowledge: The application of each model of the database to MC frameworks provides age- and gender-specific organ dose estimations from medical exposures in the head and neck region.

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

PURPOSE: To 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. METHODS: The 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. RESULTS: For orthognathic protocols, dental CBCT scanners deliver lower doses compared to MDCT scanners. The estimated effective dose (ED) was 0.32mSv for a normal resolution operation mode in Promax 3D Max, 0.27mSv in VGi-evo and 1.18mSv in the Somatom Definition Flash. For temporal bone protocols, the Somatom Force resulted in an estimated ED of 0.28mSv while for NewTom 5G the ED was 0.31 and 0.22mSv for monolateral and bilateral imaging respectively. CONCLUSIONS: Two 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.

Determination of size-specific exposure settings in dental cone-beam CT.

OBJECTIVES: To estimate the possible reduction of tube output as a function of head size in dental cone-beam computed tomography (CBCT). METHODS: A 16 cm PMMA phantom, containing a central and six peripheral columns filled with PMMA, was used to represent an average adult male head. The phantom was scanned using CBCT, with 0-6 peripheral columns having been removed in order to simulate varying head sizes. For five kV settings (70-90 kV), the mAs required to reach a predetermined image noise level was determined, and corresponding radiation doses were derived. Results were expressed as a function of head size, age, and gender, based on growth reference charts. RESULTS: The use of 90 kV consistently resulted in the largest relative dose reduction. A potential mAs reduction ranging from 7 % to 50 % was seen for the different simulated head sizes, showing an exponential relation between head size and mAs. An optimized exposure protocol based on head circumference or age/gender is proposed. CONCLUSIONS: A considerable dose reduction, through reduction of the mAs rather than the kV, is possible for small-sized patients in CBCT, including children and females. Size-specific exposure protocols should be clinically implemented. KEY POINTS: • Fixed exposure settings in CBCT results in overexposure for smaller patients • For children, considerable dose reduction is possible without compromising image quality • A reduction in mAs is more dose-efficient than a kV reduction • An optimized exposure protocol was proposed based on phantom measurements • This protocol should be validated in a clinical setting.

Reduction of scatter-induced image noise in cone beam computed tomography: effect of field of view size and position.

OBJECTIVE: To measure the effect of field of view (FOV) size and position on scatter-induced image noise in cone beam computed tomography (CBCT). STUDY DESIGN: A polymethyl methacrylate (PMMA) phantom containing air and aluminum underwent CBCT scanning, using seven FOVs ranging between 4 × 4 cm and 14 × 10 cm, positioned both centrally and according to a dental scan. Signal difference to noise ratio (SDNR) was measured on two-dimensional (2-D) projection images. RESULTS: At a central position, SDNR decreased with increasing FOV size, ranging between 9.8 (14 × 10 cm) and 10.9 (4 × 4 cm). For dental FOV positions, SDNR values were between 6.3 (14 × 10 cm) and 9.5 (4 × 4 cm). To reach a constant SDNR, a dose reduction up to 76% was possible for small FOVs compared with the 14 × 10 cm FOV. CONCLUSIONS: The use of small FOVs and peripheral FOV positioning decreases scatter at the detector, resulting in a considerable potential for reduction of radiation dose to the patient.

RADIATION PROTECTION CABIN FOR CATHETER-DIRECTED LIVER INTERVENTIONS: OPERATOR DOSE ASSESSMENT.

The number and complexity of interventional radiological procedures and in particular catheter-directed liver interventions have increased substantially. The current study investigates the reduction of personal doses when using a dedicated radiation protection cabin (RPC) for these procedures. Operator and assistant doses were assessed for 3 series of 20 chemoinfusion/chemoembolisation interventions, including an equal number of procedures with and without RPC. Whole body doses, finger doses and doses at the level of knees and eyes were evaluated with different types of TLD-100 Harshaw dosemeters. Dosemeters were also attached on the three walls of the RPC. The operator doses were significantly reduced by the RPC, but also without RPC, the doses appear to be limited as a result of thorough optimisation with existing radiation protection tools. The added value of the RPC should thus be determined by the outcome of balancing dose reduction and other aspects such as ergonomic benefits.

Longitudinal in vivo microcomputed tomography of mouse lungs: No evidence for radiotoxicity.

Before microcomputed tomography (micro-CT) can be exploited to its full potential for longitudinal monitoring of transgenic and experimental mouse models of lung diseases, radiotoxic side effects such as inflammation or fibrosis must be considered. We evaluated dose and potential radiotoxicity to the lungs for long-term respiratory-gated high-resolution micro-CT protocols. Free-breathing C57Bl/6 mice underwent four different retrospectively respiratory gated micro-CT imaging schedules of repeated scans during 5 or 12 wk, followed by ex vivo micro-CT and detailed histological and biochemical assessment of lung damage. Radiation exposure, dose, and absorbed dose were determined by ionization chamber, thermoluminescent dosimeter measurements and Monte Carlo calculations. Despite the relatively large radiation dose delivered per micro-CT acquisition, mice did not show any signs of radiation-induced lung damage or fibrosis when scanned weekly during 5 and up to 12 wk. Doubling the scanning frequency and once tripling the radiation dose as to mimic the instant repetition of a failed scan also stayed without detectable toxicity after 5 wk of scanning. Histological analyses confirmed the absence of radiotoxic damage to the lungs, thereby demonstrating that long-term monitoring of mouse lungs using high-resolution micro-CT is safe. This opens perspectives for longitudinal monitoring of (transgenic) mouse models of lung diseases and therapeutic response on an individual basis with high spatial and temporal resolution, without concerns for radiation toxicity that could potentially influence the readout of micro-CT-derived lung biomarkers. This work further supports the introduction of micro-CT for routine use in the preclinical pulmonary research field where postmortem histological approaches are still the gold standard.

Estimating cancer risk from dental cone-beam CT exposures based on skin dosimetry.

The aim of this study was to measure entrance skin doses on patients undergoing cone-beam computed tomography (CBCT) examinations, to establish conversion factors between skin and organ doses, and to estimate cancer risk from CBCT exposures. 266 patients (age 8-83) were included, involving three imaging centres. CBCT scans were acquired using the SCANORA 3D (Soredex, Tuusula, Finland) and NewTom 9000 (QR, Verona, Italy). Eight thermoluminescent dosimeters were attached to the patient's skin at standardized locations. Using previously published organ dose estimations on various CBCTs with an anthropomorphic phantom, correlation factors to convert skin dose to organ doses were calculated and applied to estimate patient organ doses. The BEIR VII age- and gender-dependent dose-risk model was applied to estimate the lifetime attributable cancer risk. For the SCANORA 3D, average skin doses over the eight locations varied between 484 and 1788 µGy. For the NewTom 9000 the range was between 821 and 1686 µGy for Centre 1 and between 292 and 2325 µGy for Centre 2. Entrance skin dose measurements demonstrated the combined effect of exposure and patient factors on the dose. The lifetime attributable cancer risk, expressed as the probability to develop a radiation-induced cancer, varied between 2.7 per million (age >60) and 9.8 per million (age 8-11) with an average of 6.0 per million. On average, the risk for female patients was 40% higher. The estimated radiation risk was primarily influenced by the age at exposure and the gender, pointing out the continuing need for justification and optimization of CBCT exposures, with a specific focus on children.

Quantification of metal artifacts on cone beam computed tomography images.

OBJECTIVES: To quantify metal artifacts obtained from a wide range of cone beam computed tomography (CBCT) devices and exposure protocols, to compare their tolerance to metals of different densities, and to provide insights regarding the possible implementation of metal artifact analysis into a QC protocol for CBCT. MATERIALS AND METHODS: A customized polymethyl methacrylate (PMMA) phantom, containing titanium and lead rods, was fabricated. It was scanned on 13 CBCT devices and one multi-slice computed tomography (MSCT) device, including high-dose and low-dose exposure protocols. Artifacts from the rods were assessed by two observers by measuring the standard deviation of voxel values in the vicinity of the rods, and normalizing this value to the percentage of the theoretical maximum standard deviation. RESULTS: For CBCT datasets, artifact values ranged between 6.1% and 27.4% for titanium, and between 10.% and 43.7% for lead. Most CBCT devices performed worse than MSCT for titanium artifacts, but all of them performed better for lead artifacts. In general, no clear improvement of metal artifacts was seen for high-dose protocols, although certain devices showed some artifact reduction for large FOV or high exposure protocols. CONCLUSIONS: Regions in the vicinity of the metal rods were moderately or gravely affected, particularly in the area between the rods. In practice, the CBCT user has very limited possibilities to reduce artifacts. Researchers and manufacturers need to combine their efforts in optimizing exposure factors and implementing metal artifact reduction algorithms.

Comparison of spatial and contrast resolution for cone-beam computed tomography scanners.

OBJECTIVE: The purpose was to evaluate the perceived spatial and contrast resolution for a wide range of cone-beam computed tomography (CBCT) devices. STUDY DESIGN: A customized polymethyl methacrylate (PMMA) phantom was developed. Inserts containing a line-pair and rod pattern were used. The phantom was scanned with 13 CBCT devices and 1 multislice CT (MSCT) device using a variety of scanning protocols. The images were presented to 4 observers for scoring. RESULTS: The observer scores showed excellent agreement. A wide range was seen in image quality between CBCT exposure protocols. Compared with the average CBCT scores, the MSCT protocols scored lower for the line-pair insert but higher for the rod insert. CONCLUSIONS: CBCT devices are generally suitable for the visualization of high-contrast structures. Certain exposure protocols can be used for depicting low-contrast structures or fine details. The user should be able to select appropriate exposure protocols according to varying diagnostic requirements.

Out-of-field contributions for IMRT and volumetric modulated arc therapy measured using gafchromic films and compared to calculations using a superposition/convolution based treatment planning system.

PURPOSE: To quantify the whole-body-dose delivered during the application of new techniques and compare them to the results obtained by treatment planning systems. The ultimate goal being the use of planning data in combination with complication data to assess the impact of low doses of ionizing radiation. METHODS: A film technique using gafchromic films to assess low doses was used on simplified phantoms and compared to data from treatment planning systems as well as a simplified whole body dose calculation system (Peridose). The types of treatment include open fields, intensity modulated radiation therapy (IMRT) and volumetric arc treatments. The film measurements were confirmed using TLDs in Alderson phantoms. In addition neutron contributions were measured as these are not taken into account in the current modern treatment planning systems, but can add significantly to the patient's whole body dose. RESULTS: Dose outside of the treatment plane diminished to 1% of the prescribed dose, this for open fields, IMRT and rotational treatments alike. Noteworthy was an increase at about 20cm from the central plane in IMRT, and in a more limited fashion for volumetric modulated arc treatment. In open fields this was not observed. Treatment planning systems were good at determining the out-of-field doses of single field treatments. In complex plans the TPS underestimated the dose to the patient. At distances greater than 20cm from the field edge, these systems did not predict any dose. The Peridose program performed well in the case of classical treatments. In the case of IMRT treatments, the overall evolution of the dose as a function of the distance to the field was well-modeled. However, an over estimation of the order of 60-80% was observed, leaving the possibility for a corrective factor based on a point measurement. Dose levels over the whole body were of the order 100mGy or higher over a complete treatment for the more complex treatments. Neutron dose levels were of the order single digit mSv for 10MV treatments. For 18MV the level of neutron contribution was in agreement with recent publications, corroborating reports that the dose from neutrons is lower than previously reported.

Effective dose range for dental cone beam computed tomography scanners.

OBJECTIVE: To estimate the absorbed organ dose and effective dose for a wide range of cone beam computed tomography scanners, using different exposure protocols and geometries. MATERIALS AND METHODS: Two Alderson Radiation Therapy anthropomorphic phantoms were loaded with LiF detectors (TLD-100 and TLD-100 H) which were evenly distributed throughout the head and neck, covering all radiosensitive organs. Measurements were performed on 14 CBCT devices: 3D Accuitomo 170, Galileos Comfort, i-CAT Next Generation, Iluma Elite, Kodak 9000 3D, Kodak 9500, NewTom VG, NewTom VGi, Pax-Uni3D, Picasso Trio, ProMax 3D, Scanora 3D, SkyView, Veraviewepocs 3D. Effective dose was calculated using the ICRP 103 (2007) tissue weighting factors. RESULTS: Effective dose ranged between 19 and 368 µSv. The largest contributions to the effective dose were from the remainder tissues (37%), salivary glands (24%), and thyroid gland (21%). For all organs, there was a wide range of measured values apparent, due to differences in exposure factors, diameter and height of the primary beam, and positioning of the beam relative to the radiosensitive organs. CONCLUSIONS: The effective dose for different CBCT devices showed a 20-fold range. The results show that a distinction is needed between small-, medium-, and large-field CBCT scanners and protocols, as they are applied to different indication groups, the dose received being strongly related to field size. Furthermore, the dose should always be considered relative to technical and diagnostic image quality, seeing that image quality requirements also differ for patient groups. The results from the current study indicate that the optimisation of dose should be performed by an appropriate selection of exposure parameters and field size, depending on the diagnostic requirements.

Development and applicability of a quality control phantom for dental cone-beam CT.

Cone-beam CT (CBCT) has shown to be a useful imaging modality for various dentomaxillofacial applications. However, optimization and quality control of dental CBCT devices is hampered due to the lack of an appropriate tool for image quality assessment. To investigate the application of different image quality parameters for CBCT, a prototype polymethyl methacrylate (PMMA) cylindrical phantom with inserts for image quality analysis was developed. Applicability and reproducibility of the phantom were assessed using seven CBCT devices with different scanning protocols. Image quality parameters evaluated were: CT number correlation, contrast resolution, image homogeneity and uniformity, point spread function, and metal artifacts. Deviations of repeated measurements were between 0.0% and 3.3%. Correlation coefficients of CBCT voxel values with CT numbers ranged between 0.68 and 1.00. Contrast-to-noise ratio (CNR) values were much lower for hydroxyapatite (0 < CNR < 7.7) than for air and aluminum (5.0 < CNR < 32.8). Noise values ranged between 35 and 419. The uniformity index was between 3.3% and 11.9%. Full width at half maximum (FWHM) measurements varied between 0.43 mm and 1.07 mm. The increase of mean voxel values surrounding metal objects ranged between 6.7% and 43.0%. Results from preliminary analyses of the prototype quality control phantom showed its potential for routine quality assurance on CBCT. Large differences in image quality performance were seen between CBCT devices. Based on the initial evaluations, the phantom can be optimized and validated.

Preservation of parotid function with uncomplicated conformal radiotherapy.

BACKGROUND AND PURPOSE: To evaluate (1) parotid function, (2) subjective xerostomia and (3) pattern of relapses after conformal parotid-sparing radiotherapy (RT) for head and neck cancer. (4) To study dose-response curves of parotid glands. MATERIAL AND METHODS: From September 1999 to November 2000, 39 head and neck cancer patients requiring bilateral neck RT were treated with a fairly simple conformal RT technique (three-field set-up+anterior lower neck field; two opposed oblique boost fields). The contralateral parotid was spared. Parotid function was assessed by salivary gland scintigraphies performed before, early (median 4 weeks) and late (median 28 weeks) after RT. Xerostomia was monitored by visual analogue scales (VAS) and LENT SOMA scores. Location of locoregional recurrences was studied in relation to the radiation fields. A dose-response curve of parotids was created using logistic regression. RESULTS: (1) Early after RT, on salivary gland scintigraphy, the mean loss of secretion function in the spared parotid was 67% and total in the non-spared. Late after RT, the mean loss remained 19% in the spared and total in the non-spared parotid. Normal excretion function was regained in 75% of the spared parotids. (2) Late after RT, 78% of patients had no, minimal or acceptable subjective xerostomia. (3) No recurrence was seen near the spared parotid (11/39 locoregional recurrences). (4) The dose-response curve of parotids showed that the mean parotid dose should preferentially be < or =20 Gy, to obtain a good chance (> or =70%) for preservation of its function on scintigraphy. CONCLUSIONS: An easy conformal parotid-sparing RT technique prevents moderate or severe subjective xerostomia in 78% of patients. In the spared parotids, nearly complete to complete recovery is obtained after 6-12 months.