Left-right Directions Research Articles

System-dependent image distortion related to gantry positions of a 0.35 T MRgRT: Characterization and the corresponding correction.

MR-guided radiotherapy with high accuracy treatment planning requires addressing MR imaging artifacts that originate from system imperfections. This work presents the characterization and corresponding correction of gantry-related imaging distortions including geometric distortion and isocenter shift in a 0.35 T magnetic resonance imaging (MRI)-guided radiotherapy (MRgRT) system using distortion vector fields (DVFs). Two phantoms, the magnetic resonance imaging distortion in 3D (MRID3D ) phantom and the Fluke phantom, along with a human volunteer were imaged at different gantry angles on a 0.35 T MR-Linac. The geometric distortion and isocenter shift were characterized for both phantom images. DVFs with a field of view extended beyond the physical boundary of the MRID3D phantom were extracted from images taken at 30° gantry angle increments, with vendor-provided distortion correction turned on and off (DstOff). These extended DVFs were then applied to the relevant phantom images to correct their geometric distortions and isocenter shift at the respective gantry angles. The extended DVFs produced from the MRID3D phantom were also applied to Fluke phantom and human MR images at their respective gantry angles. The resampled images were evaluated using structural similarity index measure (SSIM) comparison with the vendor corrected images from the MRgRT system. Geometric distortion with "mean (±SD) distortion" of 3.2±0.02, 2.9±0.02, and 1.8±0.01mm and isocenter shift (±SD) of 0.49±0.3, 0.05±0.2, and 0.01±0.03mm were present in the DstOff MRID3D phantom images in right-left (RL), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. After resampling the originally acquired images by applying extended DVFs, the distortion was corrected to 0.18±0.02, 0.09±0.01, 0.15±0.01mm, and isocenter shift was corrected to 0.14±0.05, -0.02±0.04, and -0.07±0.05mm in RL, AP, and SI directions, respectively. The Fluke phantom average geometric distortion with "mean (±SD) distortion" of 2.7±0.1mm was corrected to 0.2±0. 1mm and the average isocenter shift (±SD) of 0.51±0.2mm, and 0.05±0.03 was corrected to -0.08±0.03mm, and -0.05±0.01 in RL and AP directions, respectively. SSIM (mean±SD) of the original images to resampled images was increased from 0.49±0.02 to 0.78±0.01, 0.45±0.02 to 0.75±0.01, and 0.86±0.25 to 0.98±0.08 for MRID3D phantom, Fluke phantom, and human MR images, respectively, for all the gantry angles compared to the vendor corrected images. The gantry-related MR imaging distortion including geometric distortion and isocenter shift was characterized and a corresponding correction was demonstrated using extended DVFs on 0.35 T MRgRT system. The characterized gantry-related isocenter shift can be combined with geometric distortion correction to provide a technique for the correction of the full system-dependent distortion in an MRgRT system.

Reduction of intrafraction pancreas motion using an abdominal corset compatible with proton therapy and MRI

Background and purposeMotion mitigation is of crucial importance in particle therapy (PT) of patients with abdominal tumors to ensure high-precision irradiation. Magnetic resonance imaging (MRI) is an excellent modality for target volume delineation and motion estimation of mobile soft-tissue tumors. Thus, the aims of this study were to develop an MRI- and PT-compatible abdominal compression device, to investigate its effect on pancreas motion reduction, and to evaluate patient tolerability and acceptance. Materials and methodsIn a prospective clinical study, 16 patients with abdominal tumors received an individualized polyethylene-based abdominal corset. Pancreas motion was analyzed using time- and phase resolved MRI scans (orthogonal 2D-cine and 4D MRI) with and without compression by the corset. The pancreas was manually segmented in each MRI data set and the population-averaged center-of-mass motion in inferior-superior (IS), anterior-posterior (AP) and left–right (LR) directions was determined. A questionnaire was developed to investigate the level of patient acceptance of the corset, which the patients completed after acquisition of the planning computed tomography (CT) and MRI scans. ResultsThe corset was found to reduce pancreas motion predominantly in IS direction by on average 47 % − 51 % as found in the 2D-cine and 4D MRI data, respectively, while motion in the AP and LR direction was not significantly reduced. Most patients reported no discomfort when wearing the corset. ConclusionAn MRI- and PT-compatible individualized abdominal corset was presented, which substantially reduced breathing-induced pancreas motion and can be safely applied with no additional discomfort for the patients. The corset has been successfully integrated into our in-house clinical workflow for PT of tumors of the upper abdomen.

Characteristics of Falls Among Men's Wheelchair Rugby Players in the Rio 2016 and Tokyo 2020 Summer Paralympic Games: A Video Analysis.

Wheelchair rugby is a contact sport in which falls are common and injury rates are high, yet the characteristics of the falls are still under-reported. We investigated the fall characteristics of men's wheelchair rugby players by functional classification, using all 36 official match videos from the Rio 2016 and Tokyo 2020 summer Paralympic Games. The videos were analyzed to evaluate the number of falls, playing time when the fall occurred, playing phase (offense or defense), contact with other players, foul judgement, direction of the fall, and the body part first in contact with the floor. All 182 men's wheelchair rugby players (Rio 2016, 94; Tokyo 2020, 88) were classified as low-point players or high-point players depending on their functional classification. A total of 200 falls were detected, 27 (13.5%) for low-point players and 173 (86.5%) for high-point players. Significant differences were noted between low-point players and high-point players in the direction of the fall and body part first in contact with the floor. High-point players had more falls in the forward and left-right directions, whereas low-point players were characterized by a higher percentage of falls in the left-right and backward directions. Additionally, high-point players landed on the floor with their hands with high frequency, whereas low-point players landed with their elbows and shoulders more often. Our findings suggest the significance of devising measures to prevent falls during men's wheelchair rugby games according to their functional classification.

Simple quality assurance based on filtered back projection for geometrical/irradiation accuracy in single-isocenter multiple-target stereotactic radiotherapy.

In single-isocenter multiple-target stereotactic radiotherapy (SIMT-SRT), it is difficult to evaluate both the geometrical accuracy and absorbed dose measurement when irradiating off-isocenter targets. This study aimed to develop a simple quality assurance (QA) method to evaluate off-isocenter irradiation position accuracy in SIMT-SRT and compare its feasibility with that of a commercial device. First, we created two types of inserts and metallic balls with a diameter of 5mm to be inserted into a commercially available phantom (SIMT phantom). Second, we developed a dedicated analysis software using Python for the Winston-Lutz test (WLT). Third, an image processing software, including the filtered back-projection algorithm, was developed to analyze the images obtained using an electronic portal imaging device (EPID). Fourth, the feasibility of our method was evaluated by comparing it with the results of WLT using two commercially available phantoms: WL-QA and MultiMet-WL cubes. Notably, 92% of the results in one-dimensional deviations were within 0.26mm (EPID pixel width). The correlation coefficients were 0.52, 0.92, and 0.96 in the left-right, superior-inferior, and anterior-posterior directions, respectively. In the WLT, a maximum two-dimensional deviation of 0.70mm was detected in our method, while the deviation in the other method was within 0.5mm. The advantage of our method is that it can evaluate the geometrical accuracy at any gantry angle during dynamic rotation irradiation using a filtered back-projection algorithm, even if the target is located off the isocenter. Our method can perform WLT at arbitrary positions and is suitable for the QA of dynamic rotation irradiation using an EPID.

Cerebral hemorrhage caused by shaking adult syndrome? Evidence from biomechanical analysis using 3D motion capture and finite element models.

The present study combined three-dimensional (3D) motion capture with finite element simulation to reconstruct a real shaking adult syndrome (SAS) case and further explore the injury biomechanics of SAS. The frequency at which an adult male can shake the head of another person, head-shaking amplitude, and displacement curves was captured by the VICON 3D motion capture system. The captured shaking frequency and shaking curve were loaded on the total human model for safety (THUMS) head to simulate the biomechanical response of brain injury when a head was shaken in anterior-posterior, left-right, and left anterior-right posterior directions at frequencies of 4Hz (Hz), 5Hz, 6Hz, and 7Hz. The biomechanical response of the head on impact in the anterior, posterior, left, left anterior, and right posterior directions at the equivalent velocity of 6Hz shaking was simulated. The violent shaking frequency of the adult male was 3.2-6.8Hz; head shaking at these frequencies could result in serious cerebral injuries. SAS-related injuries have obvious directionality, and sagittal shaking can easily cause brain injuries. There was no significant difference between the brain injuries caused by shaking in the simulated frequency range (4-7Hz). Impact and shaking at an equivalent velocity could cause brain injuries, though SAS more commonly occurred due to the cumulative deformation of brain tissue. Biomechanical studies of SAS should play a positive role in improving the accuracy of forensic identification and reducing this form of abuse and torture in detention or places of imprisonment.

Accuracy of mandibular anterior subapical osteotomy by virtual planning in orthognathic surgery using patient-specific implants

IntroductionMandibular anterior subapical osteotomy (MASO) is a complementary procedure during orthognathic surgery to correct proclination or extrusion of the anterior incisors when orthodontic movements fail. The increasing use of patient-specific implants (PSI, titanium plates) in orthognathic surgery has extended to this procedure. Digital orthognathic surgery planning involves manufacturing cutting/drilling guides and specific implants to provide better accuracy and allow complex movement with reduced surgical times compared to conventional planning. This study aimed to assess the accuracy of computer-aided surgery with patient-specific implants in mobilising the MASO segment according to planning. MethodsEleven consecutive patients with mean age 26.82 years (15–41, SD = 10.65) were treated with MASO in addition to other conventional orthognathic procedures incorporating digital planning and patient-specific implants. A three-dimensional “stl” format file of the mandibular dental arch was obtained using an intraoral scanner at the end of the surgical procedure. The accuracy of the MASO segment displacement imposed by PSI was assessed by comparing preoperative 3D-planned mandibular dental arch with the immediate postoperative 3D-measured arch, using surface superimposition and 7 standard dental landmarks. Deviations between the preoperative and postoperative landmarks were calculated and compared to determine whether MASO segment repositioning is sufficiently accurate to be safely used to reposition the incisor/canine axis. ResultsQuantitative analysis revealed an absolute linear difference of 0.66 mm (SD = 0.51) between preoperative 3D digital dental arch impression and postoperative planned 3D dental arch. Overall, the median absolute discrepancies in the x-axis (right-left direction), y-axis (antero-posterior direction), and z-axis (supero-inferior direction) were respectively 0.56 mm (SD = 0.42), 0.77 mm (SD = 0.45) and 0.65 mm (SD = 0.61). ConclusionA high degree of accuracy between the virtual plan and the immediate postoperative result was observed. According to our results, PSI can be used safely with accuracy in MASO as an adjunct to other conventional orthognathic procedures.

Physical characteristics in cone beam computed Tomography (CBCT) imaging for small motion target in different directions

Purpose: Fiducial marker has been an effective and intuitive way to localize motion target for lung Stereotactic Body Radiotherapy (SBRT). However, due to the complexity for motion target imaging, the optimal target localization strategy still need to be developed to improve the efficiency and effectiveness of the clinical procedure. In this study, the golden marker moving in different directions was characterized in CBCT images for optimal localization application. Method and Materials: A Visicoil linear fiducial marker was selected for this study. The length and diameter of the marker were 5mm and 1mm. The motion was generated by Real Time Position Management (RPM) phantom from Varian Medical System. The motion was simulated to be 2.3 second breathing period and about 1cm amplitude. The motion was at three directions along the anterior-posterior (AP), left-right (LR), and In-Out (IO) of the couch. Their CBCT images were taken, and targets were done by auto-contouring with HU range from minus 900 to positive 4000. The targets were post-processed with keeping the largest part and converted to high resolution segment. Their characteristics were described by shape, volume, center of the volume and volume pixel information, which were attained by MIM Software. Results: In this CBCT study, the volume of motion visicoil gold maker were 0.283cc, 0.348cc, and 0.271cc as moving along AP, IO and LR direction. They were corresponding to 143%, 163% and 236% of the static volume. The max HUs for each moving target were 3395, 343 and 3097, which were 49 %, 13% and 44% of those of the static visicoil. The center distances comparing to those of the static targets were 0.63cm with standard deviation at 0.02cm. Conclusions: When the gold makers were applied for localization of treatment target in Lung SBRT, the geometric distance can be reflected in accurate level; however, the direction of motions could generate large HU difference, which could be one of factors resulted in local failure due to undefined boundary of tumor. And dosimetric characteristic in region of interest should be further investigated to understand the potential effect of local failure case even when marker tracking or soft tissue technique for localization is used.

A new method for assessing lung tumor motion in radiotherapy using dynamic chest radiography.

Dynamic chest radiography (DCR) is a recent advanced modality to acquire dynamic and functional images. We developed a new method using DCR and the free analysis software, Kinovea, to assess lung tumor motion. This study aimed to demonstrate the usefulness of our method. Phantom and clinical studies were performed. In the phantom study, dynamic images of a moving lead sphere were acquired using DCR, and the motion of the phantom was tracked using Kinovea in a DCR video. The amplitude of phantom motion was measured and compared with a predetermined baseline amplitude. In a clinical study, DCR and respiratory‐gated four‐dimensional computed tomography (4D‐CT) were performed on 15 patients who underwent stereotactic body radiation therapy for lung tumors. The amplitudes of tumor motion in DCR and 4D‐CT were measured in the superior‐inferior (SI), left‐right (LR), and anterior‐posterior (AP) directions, and the square root of the sum of squares (SRSS) of the amplitude was calculated in all directions. Spearman's rank correlation and the Wilcoxon signed‐rank test were performed to determine the correlations of the amplitudes of tumor motion obtained using DCR and 4D‐CT. In the phantom study, the absolute mean error between the measured and predetermined amplitudes was 0.60 mm (range: 0.061.53 mm). In the clinical study, the amplitudes of tumor motion obtained using DCR correlated significantly with those of 4D‐CT in the SI and LR directions, as did the SRSS values. The median amplitudes for DCR were significantly higher than those for 4D‐CT in all (SI, LR, and AP) directions, as were the SRSS values. Our proposed method based on DCR and Kinovea is useful for assessing lung tumor motion, visually and quantitatively. Therefore, DCR has potential as a new modality for evaluating lung tumor motion in radiotherapy.

Role of reading medium and audio distractors on visual search

PurposeVisual search is an active perceptual task influenced by objective factors and subjective factors such as task difficulty, distractors, attention and familiarity respectively. We studied the effect of different search directions, task medium and presence or absence of audio distractors on visual search time in young normal subjects MethodsTwenty-four young (19–27 years) subjects with normal ocular health (except refractive error) participated in the study after obtaining informed consent. Subjects performed a word search task of ten 7-letter words of medium difficulty level. It was performed by each subject in Up-down, Down-Up, Left-Right, Right-Left, Diagonal and Random directions, with equal number of distractors. The task was performed in paper and digital medium, with or without audio distractors. The conditions were performed in random order by each subject and the time taken to accurately complete the word search was documented for each condition. ResultThe visual search time (VST) was significantly different with different search directions (ANOVA p<0.0001, df=5), considering both digital and non-digital medium, with or without audio distractors. The average VST was the least for left-right search direction (100±7.2 s) and was highest for random search direction (291±19 s), on a digital medium (VSTdigital: 183±77 s) and in presence of an audio distractor (VSTaudio: 184±77 s). The VST scores were not correlated with the age (r=-0.14, p = 0.25). ConclusionThe visual search time is significantly delayed for search direction other than left-right direction and in presence of an audio distractor on a digital medium. These factors could play a significant role in visual orientation and specific tasks such as reading.

Comprehensive evaluation of dosimetric impact against position errors in accelerator-based BNCT under different treatment parameter settings.

BackgroundPatients who undergo accelerator‐based (AB) boron neutron capture therapy (BNCT) for head and neck cancer in the sitting position are generally uncomfortably immobilized, and patient motion during this treatment may be greater than that in other radiotherapy techniques. Furthermore, the treatment time of BNCT is relatively long (up to approximately 1 h), which increases the possibility of patient movement during treatment. As most BNCT irradiations are performed in a single fraction, the dosimetric error due to patient motion is of greater consequence and needs to be evaluated and accounted for. Several treatment parameters are required for BNCT dose calculation.PurposeTo investigate the dosimetric impacts (DIs) against position errors using a simple cylindrical phantom for an AB‐BNCT system under different treatment parameter settings.MethodsThe treatment plans were created in RayStation and the dose calculation was performed using the NeuCure® dose engine. A cylindrical phantom (16 cm diameter × 20 cm height) made of soft tissue was modeled. Dummy tumors in the form of a 3‐cm‐diameter sphere were arranged at depths of 2.5 and 6.5 cm (denoted by T 2.5 and T 6.5, respectively). Reference plans were created by setting the following parameters: collimator size = 10, 12, or 15 cm in diameter, collimator‐to‐surface distance (CSD) = 4.0 or 8.0 cm, tumor‐to‐blood ratio (T/B ratio) using 18F‐fluoro‐borono‐phenylalanine = 2.5 or 5.0, and 10B concentration in blood = 20, 25, or 30 ppm. The prescribed dose was D 95% ≥ 20 Gy‐eq for both T 2.5 and T 6.5. Based on the reference plans, phantom‐shifted plans were created in 26 directions [all combinations of left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions) and three distances (1.0, 2.0, and 3.0 cm). The DIs were evaluated at D 80% of the tumors. The shift direction dependency of the DI in the LR, AP, and SI directions was evaluated by conducting a multiple regression analysis (MRA) and other analyses where required.ResultsThe coefficients of the MRA of the DIs for LR, AP, and SI shifts were −0.08, 2.16, and −0.04 (p‐values = 0.084, <0.01, and 0.334) for T 2.5 and −0.05, 2.08, and 0.15 (p‐values = 0.526, <0.01, and 0.065) for T 6.5, respectively. The analysis of variance showed that DIs due to the AP shift were significantly greater for smaller collimator sizes on T 2.5 and smaller CSD on T 6.5. Dose reduction due to SI or LR (lateral) shifts was significantly greater for smaller collimator sizes on both T 2.5 and T 6.5 and smaller CSD on T2.5, according to the Student's t‐test. There were no significant differences in the DIs against both the AP shift and the lateral shift between the different T/B ratios and 10B concentrations.ConclusionThe DIs were largely affected by the shift in the AP direction and were influenced by the different treatment parameters.

Evaluation of internal margins for prostate for step and shoot intensity-modulated radiation therapy and volumetric modulated arc therapy using different margin formulas.

PurposeThis feasibility study evaluated the intra‐fractional prostate motion using an ultrasound image‐guided system during step and shoot intensity‐modulated radiation therapy (SS‐IMRT) and volumetric modulated arc therapy (VMAT). Moreover, the internal margins (IMs) using different margin formulas were calculated.MethodsFourteen consecutive patients with prostate cancer who underwent SS‐IMRT (n = 5) or VMAT (n = 9) between March 2019 and April 2020 were considered. The intra‐fractional prostate motion was observed in the superior–inferior (SI), anterior–posterior (AP), and left–right (LR) directions. The displacement of the prostate was defined as the displacement from the initial position at the scanning start time, which was evaluated using the mean ± standard deviation (SD). IMs were calculated using the van Herk and restricted maximum likelihood (REML) formulas for SS‐IMRT and VMAT.ResultsFor SS‐IMRT, the maximum displacements of the prostate motion were 0.17 ± 0.18, 0.56 ± 0.86, and 0.18 ± 0.59 mm in the SI, AP, and LR directions, respectively. For VMAT, the maximum displacements of the prostate motion were 0.19 ± 0.64, 0.22 ± 0.35, and 0.14 ± 0.37 mm in the SI, AP, and LR directions, respectively. The IMs obtained for SS‐IMRT and VMAT were within 2.3 mm and 1.2 mm using the van Herk formula and within 1.2 mm and 0.8 mm using the REML formula.ConclusionsThis feasibility study confirmed that intra‐fractional prostate motion was observed with SS‐IMRT and VMAT using different margin formulas. The IMs should be determined according to each irradiation technique using the REML margin.

Application of "kindergarten effect" in radiotherapy for children with tumor aged 3-5 years

To study the clinical application effect of "kindergarten effect" in radiotherapy for children with tumor based on the psychology of preschool children aged 3-5 years. A total of 30 children, aged 3-5 years, who were admitted to the Department of Radiotherapy, Tianjin Medical University Cancer Institute and Hospital, from January 2020 to August 2021 were enrolled in this prospective study. The children were randomly divided into a control group and a test group, with 15 children in each group. The children in the test group were treated in "kindergarten mode", i.e., all children were treated together at a specified time and left together after all children completed treatment. Those in the control group were treated alternately with adult patients according to the treatment time based on the type of radiotherapy fixation device. The treatment compliance was evaluated for both groups, and the two groups were compared in terms of the setup errors in the superior-inferior (SI), left-right (LR), and anterior-posterior (AP) directions. Compared with the control group, the test group showed a significantly shorter time for finishing the treatment (P<0.05) and a significantly lower proportion of children with treatment interruption (P<0.05). Compared with the control group, the test group showed smaller mean errors in the SI, LR and AP directions after image-guided radiotherapy, with significant differences in the mean errors in the SI and LR directions (P<0.05). With the application of the "kindergarten effect", most children can actively cooperate in radiotherapy, and it can also improve the accuracy and repeatability of positioning and help to achieve the desired treatment outcome.

Eliminating tattoos for short course palliative radiation therapy: Set-up error, satisfaction and cost

PurposePalliative patients are living longer thanks to advancements in systemic therapies and radiotherapy technologies. Prior to image guided radiotherapy, permanent ink tattoos were used to ensure set up accuracy. Permanent marks can cause psychological damage, physical pain and can reduce a patient’s quality of life. In recent years, image guided radiation therapy (IGRT) has become standard practice and may eliminate the need for permanent tattoos in this patient population. MethodsTwenty-five patients were consecutively chosen from the Palliative Radiation Oncology Program (PROP). Each received 5 fractions of radiotherapy commencing within 72 hours of CT simulation. In place of permanent tattoos, patients were marked with permanent marker and an adherent transparent film dressing (Tegaderm TM ) was placed over the mark. Patients were educated on maintaining the marks and dressing. Daily cone beam CT (CBCT) isocentre mismatch values were compared with 25 patients who received tattoos for radiotherapy to similar body regions. Radiation therapist concerns, cost, variations in isocentre shift values and additional imaging requirements were obtained. ResultsIsocentre shift values were similar (p<0.05) for Tegaderm TM vs. tattoo patients in the anterior-posterior (AP) and right-left (RL) directions. The mean shift value in the superior-inferior (SI) direction was larger for Tegaderm TM than for tattoos (p=0.01), however the magnitude was only 2 mm, which is clinically insignificant as these shifts were prior to IGRT guided correction. No patient required a repeat CBCT or a resimulation. The cost of the Tegaderm TM dressing was substantially less than the tattoo group. Radiation Therapists' satifaction with Tegaderm TM was overall high, however some expressed concerns with their durability and longevity. ConclusionsWe found that the use of Tegaderm TM dressing did not result in increased set-up time, mismatch error or additional imaging procedures (CBCT or CTsimulation) and moreover cost substantially less than permanent ink tattoos.

Evaluation of lung ventilation distribution using electrical impedance tomography in standing sedated horses with capnoperitoneum

ObjectiveTo determine changes in distribution of lung ventilation with increasing intra-abdominal pressure (IAP) from carbon dioxide (CO2) insufflation in standing sedated horses. Study designProspective experimental study. AnimalsA group of six healthy adult horses. MethodsEach horse was sedated with acepromazine, detomidine and butorphanol and sedation maintained with a detomidine infusion. The horse was restrained in a stocks system and a 32 electrode electrical impedance tomography (EIT) belt was wrapped around the thorax at the fifth–sixth intercostal space. EIT images and arterial blood samples for PaO2 and PaCO2, pH and lactate concentration were obtained during capnoperitoneum at 0 (baseline A), 5, 8 and 12 mmHg as IAP increased and at 8, 5, 0 (baseline B) mmHg as IAP decreased. At each IAP, after a 2 minute stabilization period, EIT images were recorded for ≥ 2 minutes to obtain five consecutive breaths. Statistical analysis was performed using anova for repeated measures with Geisser-Greenhouse correction and a Tukey’s multiple comparison test for parametric data. The relationship between PaO2 and the center of ventilation in the ventral-dorsal (CoV-VD) and right-left (CoV-RL) directions or total impedance change as a surrogate for tidal volume (ΔZVT) were tested using linear regression analysis. Significance was assumed when p ≤ 0.05. ResultsThere were no significant changes in CoV-VD, CoV-RL, PaO2, PaCO2, lactate concentration, pH, heart rate and respiratory rate with targeted IAP. There was a significant decrease in ΔZVT compared with baseline A at 5 mmHg IAP as IAP was increased. Conclusions and clinical relevanceCapnoperitoneum causes a significant decrease in ΔZVT in standing sedated horses with increasing IAP.

Radiation-induced prostate swelling during SBRT of the prostate

Background Reduced planning target volume (PTV) margins are commonly used in stereotactic body radiotherapy (SBRT) of the prostate. In addition, MR-only treatment planning is becoming more common in prostate radiotherapy and compared to CT-MRI-based contouring results in notable smaller clinical target volume (CTV). Tight PTV margins coupled with MR-only planning raise a concern whether the margins are adequate enough to cover possible volumetric changes of the prostate. The aim of this study was to evaluate the volumetric change of the prostate and its effect on PTV margin during 5x7.25 Gy SBRT of the prostate. Material and Methods Twenty patients were included in the study. Three MRI scans, first prior to treatment (baseline), second after third fraction (mid-treatment) and third after fifth fraction (end-treatment) were acquired for each patient. Prostate contours were delineated on each MRI scan and used to assess the prostate volume and maximum prostate diameter on left-right (LR), anterior-posterior (AP) and superior-inferior (SI) directions at baseline, mid- and end-treatment. Results Median (IQR) change in the prostate volume relative to the baseline was 12.0% (3.1, 17.7) and 9.2% (2.0, 18.9) at the mid- and end-treatment, respectively, and the change was statistically significant (p = 0.004 and p = 0.020, respectively). Compared to the baseline, median increase in the maximum LR, SI and AP prostate diameters were 0.8, 2.3 and 1.5 mm at mid-treatment, and 0.5, 2.5 and 2.3 mm at end-treatment, respectively. Conclusion If prostate contouring is based solely on MRI (e.g., in MR-only protocol), additional margin of 1–2 mm should be considered to account for prostate swelling. The study is part of clinical trial NCT02319239.

Quantifying stability of parameter estimates for in vivo nearly incompressible transversely-isotropic brain MR elastography

Easily computable quality metrics for measured medical data at point-of-care are important for imaging technologies involving offline reconstruction. Accordingly, we developed a new data quality metric for in vivo transversely-isotropic (TI) magnetic resonance elastography (MRE) based on a generalization of the widely accepted octahedral shear-strain calculation. The metric uses MRE displacement data and an estimate of the TI property field to yield a ‘stability map’ which predicts regions of low versus high accuracy in the resulting material property reconstructions. We can also calculate an average TI parameter stability (TIPS) score over all voxels in a region of interest for a given measurement to indicate how reliable the recovered mechanical property estimate for the region is expected to be. The calculation is rapid and places little demand on computing resources compared to the computationally intensive material property reconstruction from non-linear inversion (TI-NLI) of displacement fields, making it ideal for point-of-care evaluation of data quality. We test the predictions of the stability map for both simulated phantoms and in vivo human brain data. We used a range of different displacement datasets from vibrations applied in the anterior-posterior (AP), left-right (LR) and combined AP + LR directions. The TIPS and variability maps (noise sensitivity or variation from the mean of repeated MRE scans) were consistently anti-correlated. Notably, Spearman correlation coefficients ∣R∣>0.6 were found between variability and TIPS score for individual white matter tracts with in vivo data. These observations demonstrate the reliability and promise of this data quality metric to screen data rapidly in realistic clinical MRE applications.

Spacesuit Center of Gravity Assessments for Partial Gravity EVA Simulation in an Underwater Environment.

The objective is to analytically determine the expected CG and build hardware to measure and verify the suited subject's CG for lunar extravehicular activity (EVA) training in an underwater environment. For lunar EVAs, it is necessary for astronauts to train with a spacesuit in a simulated partial gravity environment. NASA's Neutral Buoyancy Laboratory (NBL) can provide these conditions by producing negative buoyancy for a submerged suited subject. However, it is critical that the center of gravity (CG) for the human-spacesuit system to be accurate for conditions expected during planetary EVAs. An underwater force-transducer system and individualized human-spacesuit model was created to provide real-time measurement of CG, including recommendations for weight placement locations and quantity of weight needed on the spacesuit to achieve a realistic lunar spacesuit CG. This method was tested with four suited subjects. Across tested weighout configurations, it was observed that an aft and high CG location will have large postural differences when compared to low and fore CG locations, highlighting the importance of having a proper CG. The system had an accuracy of ±5lbs of the total lunar weight and within ± 15cm for fore-aft and left-right CG directions of the model predictions. The developed method offers analytical verification of the suited subject's CG and improves simulation quality of lunar EVAs. Future suit design can also benefit by recommending hardware changes to create ideal CG locations that improve balance and mobility. The developed methodology can be used to verify a proper CG location in future planetary EVA simulations such as different reduced gravity training analogs (e.g. active cable offloading systems).

Real-time Markerless Tracking of Lung Tumors based on 2-D Fluoroscopy Imaging using Convolutional LSTM.

To investigate the feasibility of tracking targets in 2D fluor images using a novel deep learning network. Our model design aims to capture the consistent motion of tumors in fluoroscopic images by neural network. Specifically, the model is trained by generative adversarial methods. The network is a coarse-to-fine architecture design. Convolutional LSTM (Long Short-term Memory) modules are introduced to account for the time correlation between different frames of the fluoroscopic images. The model was trained and tested on a digital X-CAT phantom in two studies. Series of coherent 2D fluoroscopic images representing the full respiration cycle were fed into the model to predict the localized tumor regions. In first study to test on massive scenarios, phantoms of different scales, tumor positions, sizes, and respiration amplitudes were generated to evaluate the accuracy of the model comprehensively. In second study to test on specific sample, phantoms were generated with fixed body and tumor sizes but different respiration amplitudes to investigate the effects of motion amplitude on the tracking accuracy. The tracking accuracy was quantitatively evaluated using intersection over union (IOU), tumor area difference, and centroid of mass difference (COMD). In the first comprehensive study, the mean IOU and dice coefficient achieved 0.93±0.04 and 0.96±0.02. The mean tumor area difference was 4.34%±4.04%. And the COMD was 0.16 cm and 0.07 cm on average in SI (superior-interior) and LR (left-right) directions, respectively. In the second amplitude study, the mean IOU and dice coefficient achieved 0.98 and 0.99. The mean tumor difference was 0.17%. And the COMD was 0.03cm and 0.01 cm on average in SI and LR directions, respectively. Results demonstrated the robustness of our model against breathing variations. Our study showed the feasibility of using deep learning to track targets in x-ray fluoroscopic projection images without the aid of markers. The technique can be valuable for both pre- and during-treatment real-time target verification using fluoroscopic imaging in lung SBRT treatments.

Lung stereotactic body radiation therapy: personalized PTV margins according to tumor location and number of four-dimensional CT scans

ObjectivesTo characterise the motion of pulmonary tumours during stereotactic body radiation therapy (SBRT) and to evaluate different margins when creating the planning target volume (PTV) on a single 4D CT scan (4DCT).MethodsWe conducted a retrospective single-site analysis on 30 patients undergoing lung SBRT. Two 4DCTs (4DCT1 and 4DCT2) were performed on all patients. First, motion was recorded for each 4DCT in anterior–posterior (AP), superior-inferior (SI) and rightleft (RL) directions. Then, we used 3 different margins (3,4 and 5 mm) to create the PTV, from the internal target volume (ITV) of 4DCT1 only (PTV D1 + 3, PTV D1 + 4, PTV D1 + 5). We compared, using the Dice coefficient, the volumes of these 3 PTVs, to the PTV actually used for the treatment (PTVttt). Finally, new treatment plans were calculated using only these 3 PTVs. We studied the ratio of the D2%, D50% and D98% between each new plan and the plan actually used for the treatment (D2% PTVttt, D50% PTVttt, D50% ITVttt D98% PTVttt).Results30 lesions were studied. The greatest motion was observed in the SI axis (8.8 ± 6.6 [0.4–25.8] mm). The Dice index was higher when comparing PTVttt to PTV D1 + 4 mm (0.89 ± 0.04 [0.82–0.98]). Large differences were observed when comparing plans relative to PTVttt and PTV D1 + 3 for D98% PTVttt (0.85 ± 0.24 [0.19–1.00]).and also for D98% ITVttt (0.93 ± 0.12 [0.4–1.0]).D98% PTVttt (0.85 ± 0.24 [0.19–1.00], p value = 0.003) was statistically different when comparing plans relative to PTVttt and PTV D1 + 3. No stastistically differences were observed when comparing plans relative to PTVttt and PTV D1 + 4. A difference greater than 10% relative to D98% PTVttt was found for only in one UL lesion, located under the carina.ConclusionA single 4DCT appears feasible for upper lobe lesions located above the carina, using a 4-mm margin to generate the PTV.Advance in knowledgePropostion of a personalized SBRT treatment (number of 4DCT, margins) according to tumor location (above or under the carina).

Whole-heart non-rigid motion corrected coronary MRA with autofocus virtual 3D iNAV

PurposeRespiratory motion-corrected coronary MR angiography (CMRA) has shown promise for assessing coronary disease. By incorporating coronal 2D image navigators (iNAVs), respiratory motion can be corrected for in a beat-to-beat basis using translational correction in the foot-head (FH) and right-left (RL) directions and in a bin-to-bin basis using non-rigid motion correction addressing the remaining FH, RL and anterior-posterior (AP) motion. However, with this approach beat-to-beat AP motion is not corrected for. In this work we investigate the effect of remaining beat-to-beat AP motion and propose a virtual 3D iNAV that exploits autofocus motion correction to enable beat-to-beat AP and improved RL intra-bin motion correction. MethodsFree-breathing 3D whole-heart CMRA was acquired using a 3-fold undersampled variable-density Cartesian trajectory. Beat-to-beat 3D translational respiratory motion was estimated from the 2D iNAVs in FH and RL directions, and in AP direction with autofocus assuming a linear relationship between FH and AP movement of the heart. Furthermore, motion in RL was also refined using autofocus. This virtual 3D (v3D) iNAV was incorporated in a non-rigid motion correction (NRMC) framework. The proposed approach was tested in 12 cardiac patients, and visible vessel length and vessel sharpness for the right (RCA) and left (LAD) coronary arteries were compared against 2D iNAV-based NRMC. ResultsAverage vessel sharpness and length in v3D iNAV NRMC was improved compared to 2D iNAV NRMC (vessel sharpness: RCA: 56 ± 1% vs 52 ± 11%, LAD: 49 ± 8% vs 49 ± 7%; visible vessel length: RCA: 5.98 ± 1.37 cm vs 5.81 ± 1.62 cm, LAD: 5.95 ± 1.85 cm vs 4.83 ± 1.56 cm), however these improvements were not statistically significant. ConclusionThe proposed virtual 3D iNAV NRMC reconstruction further improved NRMC CMRA image quality by reducing artefacts arising from residual AP motion, however the level of improvement was subject-dependent.