Size specific dose estimation in pediatric CT: preliminary study and conversion factors.

The objective of this paper is to compare the differences between volumetric CT dose index (CTDIVOL) and size-specific dose estimate (SSDEWED) based on water equivalent diameter (WED) in radiation dose measurement, and explore a new method for fast calculation of SSDEWED. The imaging data of 1238 cases of head, 1152 cases of chest and 976 cases of abdominopelvic were analyzed retrospectively, and they were divided into five age groups: ≤ 0.5, 0.5 ~ ≤ 1, 1 ~ ≤ 5, 5 ~ ≤ 10 and 10 ~ ≤ 15 years according to age. The area of interest (AR), CT value (CTR), lateral diameter (LAT) and anteroposterior diameter (AP) of the median cross-sectional image of the standard scanning range and the SSDEWED were manually calculated, and a t-test was used to compare the differences between CTDIVOL and SSDEWED in different age groups. Pearson analyzed the correlations between DE and age, DE and WED, f and age, and counted the means of conversion factors in each age group, and analyze the error ratios between SSDE calculated based on the mean age group conversion factors and actual measured SSDE. The CTDIVOL in head was (9.41 ± 1.42) mGy and the SSDEWED was (8.25 ± 0.70) mGy: the difference was statistically significant (t = 55.04, P < 0.001); the CTDIVOL of chest was (2.68 ± 0.91) mGy and the SSDEWED was (5.16 ± 1.16) mGy, with a statistically significant difference (t = -218.78, P < 0.001); the CTDIVOL of abdominopelvic was (3.09 ± 1.58) mGy and the SSDEWED was (5.89 ± 2.19) mGy: the difference was also statistically significant (t = -112.28, P < 0.001). The CTDIVOL was larger than the SSDEWED in the head except for the ≤ 0.5 year subgroup, and CTDIVOL was smaller than SSDEWED within each subgroup in chest and abdominopelvic. There were strong negative correlations between f and age (head: r = -0.81; chest: r = -0.89; abdominopelvic: r = -0.86; P < 0.001). The mean values of f at each examination region were 0.81 ~ 1.01 for head, 1.65 ~ 2.34 for chest and 1.71 ~ 2.35 for abdominopelvic region. The SSDEWED could be accurately estimated using the mean f of each age subgroup. SSDEWED can more accurately measure the radiation dose of children. For children of different ages and examination regions, the SSDEWED conversion factors based on age subgroup can be quickly adjusted and improve the accuracy of radiation dose estimation.

Microwave power penetration enhancement inside an inhomogeneous human head.

The penetration of microwave power inside a human head model is improved by employing a dielectric loaded rectangular waveguide as the transmission source. A multi-layer reflection model is investigated to evaluate the combined material characteristics of different lossy human head tissues at 2.45 GHz. A waveguide loaded with a calculated permittivity of 3.62 is shown to maximise the microwave power penetration at the desired frequency. A Quartz (SiO2) loaded rectangular waveguide fed by a microstrip antenna is designed to validate the power penetration improvement inside an inhomogeneous human head phantom. A measured 1.33 dB power penetration increment is observed for the dielectric loaded waveguide over a standard rectangular waveguide at 50 mm inside the head, with an 81.9% reduction in the size of the transmission source.

Geometric and dosimetric impact of 3D generative adversarial network-based metal artifact reduction algorithm on VMAT and IMPT for the head and neck region.

BACKGROUND: We investigated the geometric and dosimetric impact of three-dimensional (3D) generative adversarial network (GAN)-based metal artifact reduction (MAR) algorithms on volumetric-modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT) for the head and neck region, based on artifact-free computed tomography (CT) volumes with dental fillings. METHODS: Thirteen metal-free CT volumes of the head and neck regions were obtained from The Cancer Imaging Archive. To simulate metal artifacts on CT volumes, we defined 3D regions of the teeth for pseudo-dental fillings from the metal-free CT volumes. HU values of 4000 HU were assigned to the selected teeth region of interest. Two different CT volumes, one with four (m4) and the other with eight (m8) pseudo-dental fillings, were generated for each case. These CT volumes were used as the Reference. CT volumes with metal artifacts were then generated from the Reference CT volumes (Artifacts). On the Artifacts CT volumes, metal artifacts were manually corrected for using the water density override method with a value of 1.0 g/cm3 (Water). By contrast, the CT volumes with reduced metal artifacts using 3D GAN model extension of CycleGAN were also generated (GAN-MAR). The structural similarity (SSIM) index within the planning target volume was calculated as quantitative error metric between the Reference CT volumes and the other volumes. After creating VMAT and IMPT plans on the Reference CT volumes, the reference plans were recalculated for the remaining CT volumes. RESULTS: The time required to generate a single GAN-MAR CT volume was approximately 30 s. The median SSIMs were lower in the m8 group than those in the m4 group, and ANOVA showed a significant difference in the SSIM for the m8 group (p < 0.05). Although the median differences in D98%, D50% and D2% were larger in the m8 group than the m4 group, those from the reference plans were within 3% for VMAT and 1% for IMPT. CONCLUSIONS: The GAN-MAR CT volumes generated in a short time were closer to the Reference CT volumes than the Water and Artifacts CT volumes. The observed dosimetric differences compared to the reference plan were clinically acceptable.

Low dose gamma irradiation pretreatment modulates the sensitivity of CNS to subsequent mixed gamma and neutron irradiation of the mouse head.

ABSTRACТPurpose: To explore if the total body γ-irradiation at a dose of 0.1 Gy 7 days prior to acute mixed γ, n-irradiation of the head at the dose of 1 Gy can reduce the harmful effects of neutron irradiation on the hippocampal functions, neuroinflammation and neurogenesis.Materials and methods: Mice were exposed to γ-radiation alone, mixed γ,n-radiation or combined γ-rays and γ,n-radiation 7 days after γ-irradiation. Two months post-irradiation, mice were tested in Open Field and in the Morris water maze. The content of microglia, astrocytes, proliferating cells and cytokines TGF-ß, TNF-α, IL-1ß, GFAP levels, hippocampal BDNF, NT-3, NT-4, NGF mRNA expression were evaluated.Results: Two months after combined irradiation, we observed impaired hippocampus-dependent cognition, which was not detected in mice exposed to γ,n-irradiation. Combined exposure and γ,n-irradiation led to a significant increase in the level of activated microglia and astrocytes in the brains. The level of pro- and anti-inflammatory cytokines in the brain and hippocampal neurotrophine's genes changed differenly after the combined exposure and γ,n-irradiation. The quantity of DCX-positive cells was reduced after γ,n-irradiation exposer alone, but increased after combined irradiation.Conclusions: Our results indicate radio-adaptive responses in brains of mice that were exposed to low-dose gamma irradiation 7 days prior to acute 1 Gy γ,n-irradiation.

Radiation doses from head, neck, chest and abdominal CT examinations: an institutional dose report.

PURPOSE: We aimed to obtain typical values for head, neck, chest, and abdominal computed tomography (CT) examinations from routine patients in 2018, and to review our data with national and international diagnostic reference levels (DRLs). METHODS: Single-phase head, neck, chest, and abdominal CT scans of adults performed in 64-slice CT in 2018 were included in this study. Radiation dose parameters of CT scans were obtained from the picture archiving and communication system of our hospital. Volumetric CT dose index (CTDIvol) and dose length product (DLP) values were recorded. Effective dose (ED) and scan length was calculated. A 16 cm diameter phantom is referenced for head CT, and 32 cm diameter phantom is referenced for neck, chest, and abdominal CT. Descriptive statistics of the variables were given according to the normality testing. RESULTS: Median CTDIvol value was 53 mGy for the head, 13.1 mGy for the neck, 8.3 mGy for the chest, and 8.6 mGy for the abdomen. Median DLP value was 988 mGy.cm for the head, 299 mGy.cm for the neck, 314 mGy.cm for the chest, and 457 mGy.cm for the abdomen. Median ED value was 2.07 mSv for the head, 1.76 mSv for the neck, 4.4 mSv for the chest, and 6.8 mSv for the abdomen. Considering national DRLs, median CTDIvol values of head, chest, and abdomen were lower, whereas median DLP and ED values of head and chest were higher. For the abdomen, the median DLP and ED values were lower. CONCLUSION: Overall radiation dose parameters obtained in this study points out the need for optimization of head CT examinations in our institution.

Investigating the transmission profiles of 808 nm laser through different regions of the rat's head.

Studying light penetration in biological tissues became a very important concern in various medical applications. It is an essential factor required to resolve the optical dose in many diagnostic and therapeutic procedures. The absorption and scattering properties of the inspected tissue control how deep the light will travel inside the tissue. However, these optical properties are highly dependent on the wavelength of the light source. In this work, the light transmission through different regions of the rat's head was investigated and the minimum laser power required to reach different parts of the head is also determined using 808-nm semiconductor laser diode. The power variation in different regions of the head is estimated using Monte Carlo simulation. Absorption and scattering coefficients of the head layers were calculated using integrating sphere measurements and Kubelka-Munk model. The absorption coefficient of the skin was 0.19 ± 0.071 mm-1, 0.024 ± 0.11 mm-1 for skull, and 0.35 ± 0.13 mm-1 for the brain, while the scattering coefficients were 7.35 ± 1.09, 2.71 ± 0.37, and 13.04 ± 0.36 mm-1 for skin, skull, and brain, respectively. The obtained results provide a relationship between laser incident power and the depth in the rat's head showing a higher optical transmission at the frontal part of the head than the middle or back regions due to the variations in the skull thickness. Therefore, the study revealed that the transmitted power of 808 nm laser at different incident locations on the head is nonlinear and variable due to different skull's thickness.

Taller staff occupationally exposed to less radiation to the temple in cardiac procedures, but risk higher doses during vascular cases.

This study aimed to evaluate the effect of nurse and doctor height on occupational dose to the temple during fluoroscopically guided cardiovascular procedures. Additionally, an evaluation of the relationship between doctor height and table height was performed. Staff exposed during fluoroscopic procedures may be at elevated risk of cardiovascular damage or oncogenesis and have demonstrated a higher incidence of subscapular cataracts. The heads of taller staff may be exposed to reduced levels of radiation due to the increased distance from the area of highest intensity X-ray scatter. Limited research has been performed investigating height as a predictor of head dose to nursing staff. The level of radiation dose at the level of the temple to the doctor (n = 25), scrub (n = 28), and scout nurse (n = 29) was measured in a prospective single-center, observational study using Philips DoseAware badges. Procedural characteristics were recorded for vascular and cardiac cases performed in three dedicated angiography suites. Data were also collected to investigate relationships between doctor height and table height. Data were collected for 1585 cardiac and 294 vascular procedures. Staff height was a statistically significant predictor of temple dose for doctors, scrub, and scout nurses when considering the full data sample. The log temple dose demonstrated an inverse relationship to staff height during cardiac procedures, but a positive relationship for scrub and scout nurses during vascular studies. This observational study has demonstrated that taller staff are exposed to less cranial exposure dose during fluoroscopically guided cardiac examinations but has revealed a positive correlation between height and temple dose during vascular procedures. It was also determined that doctor height was correlated with average procedural table height and that vascular access point influences the choice of table elevation.

Inclination angles of the ankle and head relative to the centre of mass identify gait deviations post-stroke.

BACKGROUND: Whole-body movement adjustments during gait are common post-stroke, but comprehensive ways of quantifying and evaluating gait from a whole-body perspective are lacking. RESEARCH QUESTION: Can novel kinematic variables related to Center of Mass (CoM) position discriminate side asymmetries as well as coordination between the upper and lower body during gait within persons post-stroke and compared to non-disabled controls? METHODS: Thirty-one persons post-stroke and 41 age-matched non-disabled controls walking at their self-selected speed were recorded by 3D motion capture. The Ankle-CoM Inclination Angle (A-CoMIA) and the Head-CoM Inclination Angle (H-CoMIA) defined the angle between the CoM and the ankle and the head, respectively, in the frontal plane. These angles and their angular velocities were compared between groups, and with regard to motor impairment severity during all phases of the gait cycle (GC) using a functional interval-wise testing analysis suitable for curve data. Upper and lower body coordination was assessed using cross- correlation. RESULTS: The A-CoMIA was symmetrical between body sides in persons post-stroke but larger compared to controls. The angular velocity of A-CoMIA also differed when compared to controls. The H-CoMIA was consistently asymmetrical in persons post-stroke and larger than in controls throughout the stance phase. There were only minor group differences in the angular velocity of H-CoMIA, with some side asymmetry in persons post-stroke. The A-CoMIA of the non-affected side, and the H- CoMIA, discriminated between persons with more severe impairments compared to those with milder impairments post-stroke. The variables showed strong cross- correlations in both groups. SIGNIFICANCE: The A-CoMIA and Head-CoMIA discriminated post-stroke gait from non-disabled, as well as motor impairment severity. These variables with the advantageous curve analysis during the entire GC add valuable whole-body information to existing parameters of post-stroke gait analysis through assessment of symmetry and upper and lower body coordination.

CT-based attenuation correction of whole-body radiotherapy treatment positioning devices in PET/MRI hybrid imaging.

OBJECTIVE: To implement computed tomography (CT)-based attenuation maps of radiotherapy (RT) positioning hardware and radiofrequency (RF) coils to enable hybrid positron emission tomography/magnetic resonance imaging (PET/MRI)-based RT treatment planning. MATERIALS AND METHODS: The RT positioning hardware consisted of a flat RT table overlay, coil holders for abdominal scans, coil holders for head and neck scans and an MRI compatible hip and leg immobilization device. CT images of each hardware element were acquired on a CT scanner. Based on the CT images, attenuation maps of the devices were created. Validation measurements were performed on a PET/MR scanner using a 68Ge phantom (48 MBq, 10 min scan time). Scans with each device in treatment position were performed. Then, reference scans containing only the phantom were taken. The scans were reconstructed online (at the PET/MRI scanner) and offline (via e7tools on a PC) using identical reconstruction parameters. Average reconstructed activity concentrations of the device and reference scans were compared. RESULTS: The device attenuation maps were successfully implemented. The RT positioning devices caused an average decrease of reconstructed PET activity concentration in the range between -8.3 ± 2.1% (mean ± SD) (head and neck coil holder with coils) to -1.0 ± 0.5% (abdominal coil holder). With attenuation correction taking into account RT hardware, these values were reduced to -2.0 ± 1.2% and -0.6 ± 0.5%, respectively. The results of the offline and online reconstructions were nearly identical, with a difference of up to 0.2%. CONCLUSION: The decrease in reconstructed activity concentration caused by the RT positioning devices is clinically relevant and can successfully be corrected using CT-based attenuation maps. Both the offline and online reconstruction methods are viable options.

A flexible workflow for simulating transcranial electric stimulation in healthy and lesioned brains.

Simulating transcranial electric stimulation is actively researched as knowledge about the distribution of the electrical field is decisive for understanding the variability in the elicited stimulation effect. Several software pipelines comprehensively solve this task in an automated manner for standard use-cases. However, simulations for non-standard applications such as uncommon electrode shapes or the creation of head models from non-optimized T1-weighted imaging data and the inclusion of irregular structures are more difficult to accomplish. We address these limitations and suggest a comprehensive workflow to simulate transcranial electric stimulation based on open-source tools. The workflow covers the head model creation from MRI data, the electrode modeling, the modeling of anisotropic conductivity behavior of the white matter, the numerical simulation and visualization. Skin, skull, air cavities, cerebrospinal fluid, white matter, and gray matter are segmented semi-automatically from T1-weighted MR images. Electrodes of arbitrary number and shape can be modeled. The meshing of the head model is implemented in a way to preserve the feature edges of the electrodes and is free of topological restrictions of the considered structures of the head model. White matter anisotropy can be computed from diffusion-tensor imaging data. Our solver application was verified analytically and by contrasting the tDCS simulation results with that of other simulation pipelines (SimNIBS 3.0, ROAST 3.0). An agreement in both cases underlines the validity of our workflow. Our suggested solutions facilitate investigations of irregular structures in patients (e.g. lesions, implants) or new electrode types. For a coupled use of the described workflow, we provide documentation and disclose the full source code of the developed tools.

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance.

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m2). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. Importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects.

Simulation the distribution of thermodynamic temperatures and microwave radiation of the human head.

BACKGROUND AND OBJECTIVE: The influence of biophysical parameters on the formation of microwave radiation of the human head is poorly studied. Existing approaches to modeling microwave radiation of the human head have limitations associated with simplifying the geometry of human anatomy. The article proposes methodological solutions for numerical modeling of microwave radiation of the brain biological tissues using the geometry obtained from MRI data. METHODS: The geometrical characteristics of biological tissues in model are determined using an MRI image of the head. The methodology proposed in the article allows simulation of a human body voxel models performed the Pennes bio-heat transfer equation using the Fenix software package. RESULTS: Modeling evaluations have shown that anatomical tissues heterogeneities on the surface of the head form temperature gradient of up to 2.0 K, and changes of the microwave radiation up to 0.3 K. CONCLUSIONS: Verification data made by IR thermograph practically coincide with the results of numerical modeling. The fluctuations of the brain microwave radiation are not only the result of thermal processes in its tissues, but are determined by the dynamics of its thermoregulation processes and are an indicator of changes in the physiological processes occurring in it.

Patient motion tracking for non-isocentric and non-coplanar treatments via fixed frame-of-reference 3D camera.

PURPOSE: As C-arm linac radiation therapy evolves toward faster, more efficient delivery, and more conformal dosimetry, treatments with increasingly complex couch motions are emerging. Monitoring the patient motion independently of the couch motion during non-coplanar, non-isocentric, or dynamic couch treatments is a key bottleneck to their clinical implementation. The goal of this study is to develop a prototype real-time monitoring system for unconventional beam trajectories to ensure a safe and accurate treatment delivery. METHODS: An in-house algorithm was developed for tracking using a couch-mounted three-dimensional (3D) depth camera. The accuracy of patient motion detection on the couch was tested on a 3D printed phantom created from the body surface contour exported from the treatment planning system. The technique was evaluated against a commercial optical surface monitoring system with known phantom displacements of 3, 5, and 7 mm in lateral, longitudinal, and vertical directions by placing a head phantom on a dynamic platform on the treatment couch. The stability of the monitoring system was evaluated during dynamic couch trajectories, at speeds between 10.6 and 65 cm/min. RESULTS: The proposed monitoring system agreed with the ceiling mounted optical surface monitoring system in longitudinal, lateral, and vertical directions within 0.5 mm. The uncertainty caused by couch vibration increased with couch speed but remained sub-millimeter for speeds up to 32 cm/min. For couch speeds of 10.6, 32.2, and 65 cm/min, the uncertainty ranges were 0.27- 0.73 mm, 0.15-0.87 mm, and 0.28-1.29 mm, respectively. CONCLUSION: By mounting a 3D camera in the same frame-of-reference as the patient and eliminating dead spots, this proof of concept demonstrates real-time patient monitoring during couch motion. For treatments with non-coplanar beams, multiple isocenters, or dynamic couch motion, this provides additional safety without additional radiation dose and avoids some of the complexity and limitations of room mounted systems.

Cataract Formation and Low-Dose Radiation Exposure from Head Computed Tomography (CT) Scans in Ontario, Canada, 1994-2015.

Ionizing radiation exposure to the lens of the eye is a known cause of cataractogenesis. Administrative data from the Ontario Health Insurance Program was used to examine the association between low-dose radiation exposure from head CT scans and cataract extraction surgery for 16 million Ontarians over a 22-year period (1994-2015). Subjects were grouped based on the number of head CT scans they received, and a Cox proportional hazards analysis was used to determine if there was a correlation with cataract surgery. Covariates included in the analysis were age, sex, diabetes, hypertension and prior history of intraocular surgery. To account for the potentially long latency period between radiation exposure and cataract formation, the data were analyzed incorporating a 5- and 10-year lag between head CT scan exposure and cataract surgery. Both the 5- and 10-year lagged models followed a similar trend, where only the first three head CT scans significantly increased the risk of cataract surgery by 3-8%. Individuals receiving four or more head CT scans did not have an increased cataract risk and in several cases the risk was reduced. Overall, no positive dose-response relationship was seen between the number of head CT scans received and the risk of cataract surgery. Due to the nature of the data extracted from medical records, several uncertainties exist in the analysis related to dosimetry, ultraviolet light exposure and smoking status. Nonetheless, these results do not support an association between ionizing radiation from repeated head CT scans and cataract formation.

[Measurement of out-of-field dose to the uterus during proton therapy of the head and neck]. / Mesure de la dose délivrée hors champ à l'utérus lors d'un traitement ORL par protons.

The decision to irradiate during pregnancy is based on a risk benefit compromise of two kinds: maternal risk and fetal risk. The aim of this work is to determine the foetal risk, and uterine dose measurement in proton therapy. Foetal exposure during treatment is linked to two sources: the treatment phase, and the repositioning phase. An Alderson-Rando anthropomorphic ghost (170cm, 74kg) was positioned on the table in the treatment position. A tissue-equivalent proportional counter (TEPC), adapted to the analysis of complex radiation fields (neutron and photonics), was used to determine the irradiation related to the treatment phase. An AT1123 radiation survey meter was used to measure photons generated by X-ray radiation. I dosimetry was proposed using radio-photoluminescent dosimeters, allowing for a daily check of the dose received in the uterus. The treatment phase produces higher uterine doses than the positioning phase, but these remain very low. The equivalent dose received in the uterus for the entire treatment is estimated at 840 µSv. Using a methodology for measuring the out-of-field dose with pencil beam scanning proton therapy, the foetal dose in the first trimester was well below the acceptance dose of 100 mGy determined by the International Commission on Radiological Protection.

Patient Safety Analysis in Radiation Burden of Head Computed Tomography Imaging in 1185 Neurosurgical Inpatients.

OBJECTIVE: We performed a retrospective analysis in a cohort of 1185 patients at our institution who were identified as undergoing ≥1 head computed tomography (CT) examinations during their inpatient stay on the neurosurgery service, to quantify the number, type, and associated radiation burden of head CT procedures performed by the neurosurgery service. METHODS: CT procedure records and radiology reports were obtained via database search and directly validated against records retrieved from manual chart review. Next, dosimetry data from the head CT procedures were extracted via automated text mining of electronic radiology reports. RESULTS: Among 4510 identified adult head CT procedures, 88% were standard head CT examinations. A total of 3.65 ± 3.60 head CT scans were performed during an average adult admission. The most common primary diagnoses were neoplasms, trauma, and other hemorrhage. The median cumulative effective dose per admission was 5.66 mSv (range, 1.06-84.5 mSv; mean, 8.56 ± 8.95 mSv). The median cumulative effective dose per patient was 6.4 mSv (range, 1.1-127 mSv; mean, 9.26 ± 10.0 mSv). CONCLUSIONS: The median cumulative radiation burden from head CT imaging in our cohort equates approximately to a single chest CT scan, well within accepted limits for safe CT imaging in adults. Refined methods are needed to characterize the safety profile of the few pediatric patients identified in our study.

MRIgRT head and neck anthropomorphic QA phantom: Design, development, reproducibility, and feasibility study.

PURPOSE: The purpose of this paper was to design, manufacture, and evaluate a tissue equivalent, dual magnetic resonance/computed tomography (MR/CT) visible anthropomorphic head and neck (H&N) phantom. This phantom was specially designed as an end-to-end quality assurance (QA) tool for MR imaging guided radiotherapy (MRIgRT) systems participating in NCI-sponsored clinical trials. METHOD: The MRIgRT H&N phantom was constructed using a water-fillable acrylic shell and a custom insert that mimics an organ at risk (OAR) and target structures. The insert consists of a primary and secondary planning target volume (PTV) manufactured of a synthetic Clear Ballistic gel, an acrylic OAR and surrounding tissue fabricated using melted Superflab. Radiochromic EBT3 film and thermoluminescent detectors (TLDs) were used to measure the dose distribution and absolute dose, respectively. The phantom was evaluated by conducting an end-to-end test that included: imaging on a GE Lightspeed CT simulator, planning on Monaco treatment planning software (TPS), verifying treatment setup with MR, and irradiating on Elekta's 1.5 T Unity MR linac system. The phantom was irradiated three times using the same plan to determine reproducibility. Three institutions, equipped with either ViewRay MRIdian 60 Co or ViewRay MRIdian Linac, were used to conduct a feasibility study by performing independent end-to-end studies. Thermoluminescent detectors were evaluated in both reproducibility and feasibility studies by comparing ratios of measured TLD to reported TPS calculated values. Radiochromic film was used to compare measured planar dose distributions to expected TPS distributions. Film was evaluated by using an in-house gamma analysis software to measure the discrepancies between film and TPS. RESULTS: The MRIgRT H&N phantom on the Unity system resulted in reproducible TLD doses (SD < 1.5%). The measured TLD to calculated dose ratios for the Unity system ranged from 0.94 to 0.98. The Viewray dose result comparisons had a larger range (0.95-1.03) but these depended on the TPS dose calculations from each site. Using a 7%/4 mm gamma analysis, Viewray institutions had average axial and sagittal passing rates of 97.3% and 96.2% and the Unity system had average passing rates of 97.8% and 89.7%, respectively. All of the results were within the Imaging and Radiation Oncology Core in Houston (IROC-Houston) standard credentialing criteria of 7% on TLDs, and >85% of pixels passing gamma analysis using 7%/4 mm on films. CONCLUSIONS: An MRIgRT H&N phantom that is tissue equivalent and visible on both CT and MR was developed. The results from initial reproducibility and feasibility testing of the MRIgRT H&N phantom using the tested MGIgRT systems suggests the phantom's potential utility as a credentialing tool for NCI-clinical trials.

Computational errors of the induced electric field in voxelized and tetrahedral anatomical head models exposed to spatially uniform and localized magnetic fields.

At low and intermediate frequencies, the strength of the induced electric field is used as dosimetric quantity for human protection in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. To compute the induced electric field, numerical methods based on anatomically realistic voxel models are commonly used. However, grid-based models introduce staircase approximation errors when curved surfaces are discretized with voxels, particularly in correspondence of boundaries with large differences in electrical conductivity. By contrast, those kind of artefacts are absent in tetrahedral meshes. Here, we investigate the computational errors that affect voxelized and tetrahedral head models when exposed to uniform magnetic fields at 50 Hz, and localized exposure due to transcranial magnetic stimulation. Five subjects were considered, and for each of them four voxel grids and four tetrahedral meshes were reconstructed with different resolutions. The differences in the results were characterized by comparing the induced electric fields computed using those meshes/grids. The results showed modest discrepancies in the overall electric field distributions between the various grids and meshes. However, the peak electric field strengths were erroneous for both tetrahedral and voxel models. Therefore, post-processing techniques are needed to suppress those numerical artefacts. For this purpose, the 99.99th, or lower, percentile of the electric field strength was found to remove the numerical errors. In addition, we found that spatially averaging the electric fields over 2 mm cubical volumes, as described by the ICNIRP, was effective in removing most of the spuriously large electric fields. When spatial averaging was used, relative coarse head models consisting of approximately 1 mm voxels or tetrahedral meshes with 2 mm average side length were sufficient to mitigate the artefacts. Nonetheless, the additional percentile filtering might still be needed to suppress the erroneous values completely.

DEVELOPMENT OF A JAPANESE INFANT HEAD-CHEST PHANTOM AND INVESTIGATION OF THE CURRENT STATUS OF INFANT HEAD CT EXAMINATIONS IN JAPAN.

The aim of this study was to develop a head-chest phantom that could mimic the physique of a Japanese 0.5-year-old child and to investigate the current status of exposure dose in infant head computed tomography examinations in Japan. The phantom was produced by machine processing, and radiophotoluminescence glass dosemeters were installed in the phantom for dose measurement. Organ doses were measured for seven different head scan protocols routinely used in three hospitals. In this study, the average dose of the brain and lens within the scan region was equivalent to that measured using infant phantoms in previous studies. In contrast, the doses of both salivary glands and thyroid glands adjacent to the scan region were 1.4-1.8 times higher than those in previous studies. Expansion of the scan area accompanied by a transition of the scan mode from non-helical to helical may have resulted in the differences in organ doses.

Fractionated head and neck irradiation impacts taste progenitors, differentiated taste cells, and Wnt/ß-catenin signaling in adult mice.

Head and neck cancer patients receiving conventional repeated, low dose radiotherapy (fractionated IR) suffer from taste dysfunction that can persist for months and often years after treatment. To understand the mechanisms underlying functional taste loss, we established a fractionated IR mouse model to characterize how taste buds are affected. Following fractionated IR, we found as in our previous study using single dose IR, taste progenitor proliferation was reduced and progenitor cell number declined, leading to interruption in the supply of new taste receptor cells to taste buds. However, in contrast to a single dose of IR, we did not encounter increased progenitor cell death in response to fractionated IR. Instead, fractionated IR induced death of cells within taste buds. Overall, taste buds were smaller and fewer following fractionated IR, and contained fewer differentiated cells. In response to fractionated IR, expression of Wnt pathway genes, Ctnnb1, Tcf7, Lef1 and Lgr5 were reduced concomitantly with reduced progenitor proliferation. However, recovery of Wnt signaling post-IR lagged behind proliferative recovery. Overall, our data suggest carefully timed, local activation of Wnt/ß-catenin signaling may mitigate radiation injury and/or speed recovery of taste cell renewal following fractionated IR.