Visualization Of Soft Tissues Research Articles

Virtual CT Myelography: A Patch-Based Machine Learning Model to Improve Intraspinal Soft Tissue Visualization on Unenhanced Dual-Energy Lumbar Spine CT

Background: Distinguishing between the spinal cord and cerebrospinal fluid (CSF) non-invasively on CT is challenging due to their similar mass densities. We hypothesize that patch-based machine learning applied to dual-energy CT can accurately distinguish CSF from neural or other tissues based on the center voxel and neighboring voxels. Methods: 88 regions of interest (ROIs) from 12 patients’ dual-energy (100 and 140 kVp) lumbar spine CT exams were manually labeled by a neuroradiologist as one of 4 major tissue types (water, fat, bone, and nonspecific soft tissue). Four-class classifier convolutional neural networks were trained, validated, and tested on thousands of nonoverlapping patches extracted from 82 ROIs among 11 CT exams, with each patch representing pixel values (at low and high energies) of small, rectangular, 3D CT volumes. Different patch sizes were evaluated, ranging from 3 × 3 × 3 × 2 to 7 × 7 × 7 × 2. A final ensemble model incorporating all patch sizes was tested on patches extracted from six ROIs in a holdout patient. Results: Individual models showed overall test accuracies ranging from 99.8% for 3 × 3 × 3 × 2 patches (N = 19,423) to 98.1% for 7 × 7 × 7 × 2 patches (N = 1298). The final ensemble model showed 99.4% test classification accuracy, with sensitivities and specificities of 90% and 99.6%, respectively, for the water class and 98.6% and 100% for the soft tissue class. Conclusions: Convolutional neural networks utilizing local low-level features on dual-energy spine CT can yield accurate tissue classification and enhance the visualization of intraspinal neural tissue.

Intraoperative Ultrasound in Spinal Surgery

Since the 1980s, there have been several reports for the use of intraoperative ultrasound as a useful adjunct in spinal surgery. However, with the advent of newer cutting-edge imaging modalities, the use of intraoperative ultrasound in spine surgery has largely fallen out of favor. Despite this, intraoperative ultrasound continues to provide several advantages over other intraoperative techniques such as magnetic resonance imaging and computed tomography including being more cost-effective, efficient, and easy to operate and interpret. Additionally, it remains the only method for the real-time visualization of soft tissue and pathologies. This paper focuses on the advantages of using intraoperative ultrasound, especially in cases of intradural lesions and lesions ventral to the thecal sac when approaching posteriorly.

Sequence of actions for visualization of soft tissue hemorrhages/hematomas in elderly patients infected with SARS-CoV-2

Aim. To determine ultrasound, computed tomography and angiographic image characteristics for soft tissue hemorrhages/hematomas, the sequence of using imaging methods in patients infected with SARS-CoV-2, to study the morphology of changes in soft tissues, to determine the essence of the concept and to develop treatment tactics for this complication of COVID-19.Material and methods. During 4 months of treatment of elderly patients (+60) infected with SARS-CoV-2, 40 patients were identified with soft tissue hemorrhages/hematomas, of which 26 (65%) patients with large hematomas (>10 cm in size and > 1000 ml in volume). The analysis of clinical and laboratory parameters, methods of instrumental diagnostics (ultrasound – 26 patients, CT – 10 patients, angiography – 9 patients, punctures – 6 patients) was carried out; autopsy material was studied in 11 cases.Results. Image characteristics of hemorrhages/hematomas of soft tissue density were obtained using modern instrumental methods, and the sequence of application of visualization methods was determined. A tactic for managing a patient with stopped and ongoing bleeding has been developed. The morphological substrate of hemorrhagic complications in a new viral infection was studied. All patients were treated with conservative and minimally invasive procedures (embolization, puncture with pressure bandage). 15 patients (57.7%) recovered, 11 patients (42.3%) died from the progression of COVID-19 complications.Conclusion. Comprehensive clinical and laboratory sequential instrumental diagnosis of soft tissue hemorrhages in COVID-19. Treatment should be conservative and significantly invasive. The use of the term “soft tissue hematoma” in SARS-CoV-2 infected patients is not a natural quality of the normal pathological process and should not be observed from our point of view.

Clinical implementation of kVCT-guided tomotherapy with ClearRT.

A helical fan-beam kilovoltage computed tomography (kVCT) was recently introduced into Tomotherapy units. This study aims to share the initial experience of kVCT in clinical workflow, compare its performance with that of the existing megavoltage computed tomography (MVCT), and explore its potential in adaptive planning. We retrospectively enrolled 23 patients who underwent both MVCT and kVCT scans. The clinical performance data regarding image acquisition time, nominal dose length product (DLP), registration time and registration corrections were extracted and compared. Image quality was scored by six experienced radiation therapists and quantified based on phantom measurements. CT number stability and the implementation of adaptive radiotherapy were dosimetrically evaluated by performing the dose recalculation on kVCT. Compared to MVCT, kVCT significantly reduced DLP (except the highest kVp protocol), image acquisition and registration time. KVCT obtained higher scores than MVCT on all criteria except artifacts. Phantom measurements also revealed a better image performance characterization of kVCT except for image uniformity. The CT number variation could lead to a dose difference of 0.5% for D95% of target and Dmean of organ-at-risk. For the treatment planning with kVCT, a systematic dose difference (> 1%) in PTV dose metrics was observed at regions with large longitudinal density discontinuities compared to the reference plans. The new kVCT imaging provides enhanced soft-tissue visualization. The improved efficiency with kVCT-guided treatment will allow more patients to be treated each day. In most cases, the dose calculation accuracy of kVCT images is acceptable except for regions with severe artifacts.

Diagnostic Performance of Advanced Metal Artifact Reduction MRI for Periprosthetic Shoulder Infection.

The diagnosis of periprosthetic shoulder infection (PSI) in patients with a painful arthroplasty is challenging. Magnetic resonance imaging (MRI) may be helpful, but shoulder implant-induced metal artifacts degrade conventional MRI. Advanced metal artifact reduction (MARS) improves the visibility of periprosthetic bone and soft tissues. The purpose of our study was to determine the reliability, repeatability, and diagnostic performance of advanced MARS-MRI findings for diagnosing PSI. Between January 2015 and December 2019, we enrolled consecutive patients suspected of having PSI at our academic hospital. All 89 participants had at least 1-year clinical follow-up and underwent standardized clinical, radiographic, and laboratory evaluations and advanced MARS-MRI. Two fellowship-trained musculoskeletal radiologists retrospectively evaluated the advanced MARS-MRI studies for findings associated with PSI in a blinded and independent fashion. Both readers repeated their evaluations after a 2-month interval. Interreader reliability and intrareader repeatability were assessed with κ coefficients. The diagnostic performance of advanced MARS-MRI for PSI was quantified using sensitivity, specificity, and the area under the receiver operating characteristic curve (AUC). When applying the International Consensus Meeting (ICM) 2018 criteria, of the 89 participants, 22 (25%) were deemed as being infected and 67 (75%) were classified as being not infected (unlikely to have PSA and not requiring a surgical procedure during 1-year follow-up). The interreader reliability and intrareader repeatability of advanced MARS-MRI findings, including lymphadenopathy, joint effusion, synovitis, extra-articular fluid collection, a sinus tract, rotator cuff muscle edema, and periprosthetic bone resorption, were good (κ = 0.61 to 0.80) to excellent (κ > 0.80). Lymphadenopathy, complex joint effusion, and edematous synovitis had sensitivities of >85%, specificities of >90%, odds ratios of >3.6, and AUC values of >0.90 for diagnosing PSI. The presence of all 3 findings together yielded a PSI probability of >99%, per logistic regression analysis. Our study shows the clinical utility of advanced MARS-MRI for diagnosing PSI when using the ICM 2018 criteria as the reference standard. Although the reliability and diagnostic accuracy were high, these conclusions are based on our specific advanced MARS-MRI protocol interpreted by experienced musculoskeletal radiologists. Investigations with larger sample sizes are needed to confirm these results. Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Synchrotron X-ray biosample imaging: opportunities and challenges.

Synchrotron radiation phase-contrast microtomography is sensitive to low attenuating tissues, giving an alternative visualisation of the sample and being useful for investigating microstructure inside biological specimens without staining them with a contrast medium. The phase-contrast technique has been widely used in the scientific community, as it is a technique associated with radiography and microscopy and able to enhance contrast in soft tissues, specifically at the edges, showing details that could not be seen by the absorption technique. This work aims to show the ability of synchrotron-based phase-contrast microtomography for the visualisation of soft tissues and hard internal structures of millimetre-sized biological organisms. Case studies of the anatomy of Rhodnius prolixus head and Thoropa miliaris tadpole are presented to illustrate the imaging technique.

Micro-Computed Tomography Soft Tissue Biological Specimens Image Data Visualization

Visualization of soft tissues in microCT scanning using X-rays is still a complicated matter. There is no simple tool or methodology on how to set up an optimal look-up-table while respecting the type of soft tissue. A partial solution may be the use of a contrast agent. However, this must be accompanied by an appropriate look-up-table setting that respects the relationship between the soft tissue type and the Hounsfield units. The main aim of the study is to determine experimentally derived look-up-tables and relevant values of the Hounsfield units based on the statistical correlation analysis. These values were obtained from the liver and kidneys of 24 mice in solutions of ethanol as the centroid value of the opacity look-up-table area under this graph. Samples and phantom were scanned by a Bruker SkyScan 1275 micro-CT and Phywe XR 4.0 and processed using CTvox and ORS Dragonfly software. To reconstruct the micro-CT projections, NRecon software was used. The main finding of the study is that there is a statistically significant relationship between the centroid of the area under the look-up-table curve and the number of days for which the animal sample was stored in an ethanol solution. H1 of the first hypothesis, i.e. that suggested the Spearman’s correlation coefficient does not equal zero (r1 ≠ 0) regarding this relationship was confirmed. On the other hand, there is no statistically significant relationship between the centroid of the area under the look-up-table curve and the concentration of the ethanol solution. In this case, H1 of the second hypothesis, i.e. that the Spearman’s correlation coefficient does not equal zero (r2 ≠ 0) regarding this relationship was not confirmed. Spearman’s correlation coefficients were −0.27 for the concentration and −0.87 for the number of days stored in ethanol solution in the case of the livers of 13 mice and 0.06 for the concentration and 0.94 for the number of days stored in ethanol solution in the case of kidneys of 11 mice.

Prostate Volume Changes during Extreme and Moderately Hypofractionated Magnetic Resonance Image-guided Radiotherapy

AimsProstate morphological changes during external beam radiotherapy are poorly understood. Excellent soft-tissue visualisation offered by magnetic resonance image-guided radiotherapy (MRIgRT) provides an opportunity to better understand such changes. The aim of this study was to quantify prostate volume and dimension changes occurring during extreme and moderately hypofractionated schedules. Materials and methodsForty prostate cancer patients treated on the Unity 1.5 Tesla magnetic resonance linear accelerator (MRL) were retrospectively reviewed. The cohort comprised patients treated with 36.25 Gy in five fractions (n = 20) and 60 Gy in 20 fractions (n = 20). The volume of the delineated prostates on reference planning computed tomography (fused with MRI) and daily T2-weighted 2-min session images acquired on Unity were charted. Forty planning computed tomography and 500 MRL prostate volumes were evaluated. The mean absolute and relative change in prostate volume during radiotherapy was compared using a paired t-test (P value <0.01 considered significant to control for multiple comparisons). The maximum dimension of the delineated prostate was measured in three isocentric planes. ResultsSignificant prostate volume changes, relative to MRL imaging fraction 1 (MRL#1), were seen at all time points for the five-fraction group. The peak mean relative volume increase was 21% (P < 0.001), occurring at MRL#3 and MRL#4 after 14.5 and 21.75 Gy, respectively. Prostate expansion was greatest in the superior–inferior direction; the peak mean maximal extension was 5.9 mm. The maximal extension in the left–right and anterior–posterior directions measured 1.1 and 2.2 mm, respectively. For the 20-fraction group, prostate volume increased relative to MRL#1, for all treatment time points. The mean relative volume increase was 11% (P < 0.001) at MRL#5 after 12 Gy, it then fluctuated between 8 and 13%. From MRL#5 to MRL#20, the volume increase was significant (P < 0.01) for 12 of 16 time points calculated. The peak mean maximal extension in the superior–inferior direction was 3.1 mm. The maximal extension in the left–right and anterior–posterior directions measured 1.7 and 3.7 mm, respectively. ConclusionSignificant prostate volume and dimension changes occur during extreme and moderately hypofractionated radiotherapy. The extent of change was greater during extreme hypofractionation. MRIgRT offers the opportunity to reveal, quantify and correct for this deformation.

Diffusible contrast-enhanced micro-CT improves visualization of stented vessels

In this report, we showcase diffusible iodine-based contrast-enhanced computed tomography (DICE-CT) as a method for improving soft tissue visualization and reducing beam hardening artifact within a stented vessel. This technique is commonly used in our pathology lab to image soft tissue specimens with dense metal implants and to ensure reliable morphological analysis through clear delineation of tissue structures. For this report, a porcine right coronary artery with an implanted metal stent was scanned using both conventional and DICE-CT methods. Upon reconstruction, DICE-CT produced less beam hardening artifact in comparison to traditional micro-CT; furthermore, DICE-CT produced results with morphometric similarity to histology. Accordingly, these differences illustrated the clear advantage of using DICE-CT over conventional micro-CT when imaging soft tissue specimens with dense metal implants.

DeBoNet: A deep bone suppression model ensemble to improve disease detection in chest radiographs.

Automatic detection of some pulmonary abnormalities using chest X-rays may be impacted adversely due to obscuring by bony structures like the ribs and the clavicles. Automated bone suppression methods would increase soft tissue visibility and enhance automated disease detection. We evaluate this hypothesis using a custom ensemble of convolutional neural network models, which we call DeBoNet, that suppresses bones in frontal CXRs. First, we train and evaluate variants of U-Nets, Feature Pyramid Networks, and other proposed custom models using a private collection of CXR images and their bone-suppressed counterparts. The DeBoNet, constructed using the top-3 performing models, outperformed the individual models in terms of peak signal-to-noise ratio (PSNR) (36.7977±1.6207), multi-scale structural similarity index measure (MS-SSIM) (0.9848±0.0073), and other metrics. Next, the best-performing bone-suppression model is applied to CXR images that are pooled from several sources, showing no abnormality and other findings consistent with COVID-19. The impact of bone suppression is demonstrated by evaluating the gain in performance in detecting pulmonary abnormality consistent with COVID-19 disease. We observe that the model trained on bone-suppressed CXRs (MCC: 0.9645, 95% confidence interval (0.9510, 0.9780)) significantly outperformed (p < 0.05) the model trained on non-bone-suppressed images (MCC: 0.7961, 95% confidence interval (0.7667, 0.8255)) in detecting findings consistent with COVID-19 indicating benefits derived from automatic bone suppression on disease classification. The code is available at https://github.com/sivaramakrishnan-rajaraman/Bone-Suppresion-Ensemble.

Synthetic CT for the planning of MR-HIFU treatment of bone metastases in pelvic and femoral bones: a feasibility study

ObjectivesVisualization of the bone distribution is an important prerequisite for MRI-guided high-intensity focused ultrasound (MRI-HIFU) treatment planning of bone metastases. In this context, we evaluated MRI-based synthetic CT (sCT) imaging for the visualization of cortical bone.MethodsMR and CT images of nine patients with pelvic and femoral metastases were retrospectively analyzed in this study. The metastatic lesions were osteolytic, osteoblastic or mixed. sCT were generated from pre-treatment or treatment MR images using a UNet-like neural network. sCT was qualitatively and quantitatively compared to CT in the bone (pelvis or femur) containing the metastasis and in a region of interest placed on the metastasis itself, through mean absolute difference (MAD), mean difference (MD), Dice similarity coefficient (DSC), and root mean square surface distance (RMSD).ResultsThe dataset consisted of 3 osteolytic, 4 osteoblastic and 2 mixed metastases. For most patients, the general morphology of the bone was well represented in the sCT images and osteolytic, osteoblastic and mixed lesions could be discriminated. Despite an average timespan between MR and CT acquisitions of 61 days, in bone, the average (± standard deviation) MAD was 116 ± 26 HU, MD − 14 ± 66 HU, DSC 0.85 ± 0.05, and RMSD 2.05 ± 0.48 mm and, in the lesion, MAD was 132 ± 62 HU, MD − 31 ± 106 HU, DSC 0.75 ± 0.2, and RMSD 2.73 ± 2.28 mm.ConclusionsSynthetic CT images adequately depicted the cancellous and cortical bone distribution in the different lesion types, which shows its potential for MRI-HIFU treatment planning.Key Points• Synthetic computed tomography was able to depict bone distribution in metastatic lesions.• Synthetic computed tomography images intrinsically aligned with treatment MR images may have the potential to facilitate MR-HIFU treatment planning of bone metastases, by combining visualization of soft tissues and cancellous and cortical bone.

Stereotactic radiotherapy and the potential role of magnetic resonance-guided adaptive techniques for pancreatic cancer.

BACKGROUNDPancreatic cancer is a malignancy with one of the poorest prognoses amongst all cancers. Patients with unresectable tumours either receive palliative care or undergo various chemoradiotherapy regimens. Conventional techniques are often associated with acute gastrointestinal toxicities, as adjacent critical structures such as the duodenum ultimately limits delivered doses. Stereotactic body radiotherapy (SBRT) is an advanced radiation technique that delivers highly ablative radiation split into several fractions, with a steep dose fall-off outside target volumes. AIMTo discuss the latest data on SBRT and whether there is a role for magnetic resonance-guided techniques in multimodal management of locally advanced, unresectable pancreatic cancer.METHODSWe conducted a search on multiple large databases to collate the latest records on radiotherapy techniques used to treat pancreatic cancer. Out of 1229 total records retrieved from our search, 36 studies were included in this review.RESULTSStudies indicate that SBRT is associated with improved clinical efficacy and toxicity profiles compared to conventional radiotherapy techniques. Further dose escalation to the tumour with SBRT is limited by the poor soft-tissue visualisation of computed tomography imaging during radiation planning and treatment delivery. Magnetic resonance-guided techniques have been introduced to improve imaging quality, enabling treatment plan adaptation and re-optimisation before delivering each fraction.CONCLUSIONTherefore, SBRT may lead to improved survival outcomes and safer toxicity profiles compared to conventional techniques, and the addition of magnetic resonance-guided techniques potentially allows dose escalation and conversion of unresectable tumours to operable cases.

In Vitro Preparation of Actively Maturing Bovine Articular Cartilage Explants for X-Ray Phase Contrast Imaging.

Understanding the mechanisms that underpin post-natal maturation of articular cartilage is of crucial importance for designing the next generation of tissue engineering strategies and potentially repairing diseased or damaged cartilage. In general, postnatal maturation of the articular cartilage, which is a wholesale change in collagen structure and function of the tissue to accommodate growth of the organism, occurs over a timescale ranging from months to years. Conversely dissolution of the structural organization of the cartilage that also occurs over long timescales is the hallmark of tissue degeneration. Our ability to study these biological processes in detail have been enhanced by the findings that growth factors can induce precocious in vitro maturation of immature articular cartilage. The developmental and disease related changes that occur in the joint involve bone and cartilage and an ability to co-image these tissues would significantly increase our understanding of their intertwined roles. The simultaneous visualization of soft tissue, cartilage and bone changes is nowadays a challenge to overcome for conventional preclinical imaging modalities used for the joint disease follow-up. Three-dimensional X-ray Phase-Contrast Imaging methods (PCI) have been under perpetual developments for 20 years due to high performance for imaging low density objects and their ability to provide additional information compared to conventional X-ray imaging. In this protocol we detail the procedure used in our experiments from biopsy of the cartilage, generation of in vitro matured cartilage to data analysis of image collected using X-ray phase contrast imaging.

Breast DCE-MRI in long-term breast cancer survivors: What lies beneath dystrophic calcifications due to fat necrosis?

Breast cancer becomes a chronic condition due to advances in diagnosis and treatment. This fact emphasizes the awareness of late post-treatment sequelae, such as dystrophic calcifications due to fat necrosis. In the case of extremely numerous, diffuse dystrophic calcifications, a coexistent carcinoma can be masked on the clinical, mammographic and ultrasound examination. Breast dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a problem solving tool, allowing visualization of soft tissues and detection of angiogenesis.

Dose accumulation of daily adaptive plans to decide optimal plan adaptation strategy for head-and-neck patients treated with MR-Linac.

Advances in magnetic resonance linear accelerators (MR-Linacs) allow for superior visualization of soft tissue to guide online adaptive replanning for precise radiotherapy delivery. Elekta Unity MR-Linacs (Elekta AB, Stockholm, Sweden) provides 2 plan adaptation approaches, adapt-to-position (ATP), plan reoptimization based on the reference CT with the iso-shift measured from daily MR scans, and adapt-to-shape (ATS), full plan reoptimization based on the re-contoured daily MR scans. Our study aims to close the gap in knowledge regarding the use of the ATP technique in the treatment of head and neck (HN) cancers through the analysis of accumulated dose of daily ATP plans to organs at risk (OARs). Daily accumulated doses of 8 HN patients using deformable registration were analyzed to estimate the actual delivered dose versus the planned dose to evaluate the impact from daily anatomical changes and setup uncertainties. This process was completed through the collection of doses to OARs which were chosen based on the rigidity and size of the organ and the substantial dose it received. Results showed that the actual dose delivered to some OARs was significantly higher than the originally planned dose and was more pronounced in structures that were within the high-dose gradient for some subdisease sites. These findings suggest that the ATS approach should be used for plan adaptation in some specific HN diseases where OARs receive substantial dose with anatomy changes that could not be accounted for by the ATP approach. We also investigated the possibility of predicting the actual delivered dose at an early stage of the treatment course, with the intention of exploring a possibly more optimal alternative for planning through the combination of ATP and ATS approaches throughout treatment.

Modern approaches to the elimination of artifacts of cone-beam computed tomography of the maxillofacial region

The use of X-ray radiation is the main additional method for complete visualization of hard and soft tissues in dentistry and maxillofacial surgery. Cone-beam computed tomography (CBCT) is of leading importance among other methods. Three-dimensional reformation of CBCT data into a multiplanar or three-dimensional image of anatomical structures allows for a qualitative assessment of the area of interest and to choose the right treatment tactics if necessary. Nevertheless, there are a number of factors or artifacts that lead to distortion, disrupt the image or lead to loss of information during CBCT, in addition, the formation of overdiagnosis is not excluded. Currently, an active search is underway for ways to improve the quality of CBCT images and eliminate artifacts to improve the quality of diagnostics. This review is devoted to the description of the main causes of artifacts and modern methods of their elimination.

Tantalum Oxide Nanoparticles for the Quantitative Contrast-Enhanced Computed Tomography of Ex Vivo Human Cartilage: Assessment of Biochemical Composition and Biomechanics.

Nanoparticle-based contrast agents, when used in concert with imaging modalities such as computed tomography (CT), enhance the visualization of tissues and boundary interfaces. However, the ability to determine the physiological state of the tissue via the quantitative assessment of biochemical or biomechanical properties remains elusive. We report the synthesis and characterization of tantalum oxide (Ta2O5) nanoparticle (NP) contrast agents for rapid, nondestructive, and quantitative contrast-enhanced computed tomography (CECT) to assess both the glycosaminoglycan (GAG) content and the biomechanical integrity of human metacarpal phalangeal joint (MCPJ) articular cartilage. Ta2O5 NPs 3-6 nm in diameter and coated with either nonionic poly(ethylene) glycol (PEG) or cationic trimethylammonium ligands readily diffuse into both healthy and osteoarthritic MCPJ cartilage. The CECT attenuation for the cationic and neutral NPs correlates with the glycosaminoglycan (GAG) content (R2 = 0.8975, p < 0.05 and 0.7054, respectively) and the equilibrium modulus (R2 = 0.8285, p < 0.05 and 0.9312, p < 0.05, respectively). The results highlight the importance of the surface charge and size in the design of NP agents for targeting and imaging articular cartilage. Further, nanoparticle CECT offers the visualization of both soft tissue and underlying bone unlike plain radiography, which is the standard for imaging bone in musculoskeletal diseases, and the ability to provide a real-time quantitative assessment of both hard and soft tissues to provide a comprehensive image of the disease stage, as demonstrated herein.

New CBCT Indications in Musculoskeletal Imaging

Cone-beam computed tomography (CBCT) has become increasingly important as a low-radiation imaging technique with high resolution. The current new generation CBCT’s aim to optimize the benefits of CBCT while limiting the traditional disadvantages with features such as a larger gantry, higher tube voltage and a moveable table. Very promising is the current development of dual energy CBCT for detecting bone marrow edema, a better soft tissue visualization and reduction of beam hardening artifact. implementation of iterative reconstructions and artificial intelligence in high-end CBCT is a potential tool in a further very substantial dose reduction.

Novel modified patient immobilisation device with an integrated coil support system for MR-guided online adaptive radiotherapy in the management of brain and head-and-neck tumours.

Magnetic resonance imaging (MR)-guided online adaptive radiotherapy is a promising technique in the field of radiation oncology providing excellent visualisation of soft-tissues, and allowing for online plan adaptation and tumour tracking. In order to facilitate the accurate dose delivery to the target volume while sparing healthy surrounding normal tissue in the brain or head-and-neck (H&N) region, precise patient immobilisation with good image quality is pertinent. Herein, we present a customised thermoplastic mask holder with an integrated anterior MR receiver coil support system for MR-guided online adaptive radiotherapy in the brain and head-and-neck region. The approved medical product was developed by Innovative Technologie Voelp (IT-V), Innsbruck, Austria. MR image uniformity measurements demonstrated improved image uniformity at the expense of decreased signal-to-noise ratio due to a more defined and larger distance between the anterior receiver coil and the phantom or patient. This integrated coil support system represents a practical solution facilitating stable and reproducible anterior coil placement while maintaining the thermoplastic mask holder functionality, a widely established immobilisation technique.

Dosimetric and Clinical Evaluation of Stereotactic MR-Guided Online Adaptive Radiation Therapy (SMART) for Treatment of Adrenal Metastases

Stereotactic MR-guided Adaptive Radiotherapy (SMART) is an appealing treatment option for irradiation of intra-abdominal tumors. Daily adaptation with SMART has the advantage of dose escalation while protecting organs at risk (OARs). We aimed to document dosimetric parameters during SMART and analyze local control for adrenal metastases.Fifteen patients treated between September 2018 and October 2020 for adrenal metastases were included in the study. The institutional constraints were used to evaluate the doses to OARs and target volumes. For each fraction, an adaptive plan was generated following registration and delineation of the daily disposition. A comparison was done between predicted plans (original plan on the daily anatomy) and adapted plans (new plan after re-optimization accounting the new contours) in terms of target volumes coverage and OARs doses. Patients were treated every other day.The median age was 63 years (range 36-74 years) and 73.3% of patients were male. The median delivered total dose was 50 Gy (range 35-50 Gy); with a median fraction number of 5 (range 3-5 fractions) and the median fraction dose was 10 Gy (range 7-15 Gy), corresponding to a median BED10 of 100 Gy (range 60-113 Gy). Nine patients presented with a left-sided lesion, five with right-sided and one patient with both left and right-sided lesions. All of the initial plans met target and OARs constraints. Among 70 fractions 56 fractions (80%) were re-optimized. The dosimetric findings for PTV and OARs on predicted and re-optimized fractions were compared. PTV V100 (90.9% vs 94.3%) and PTV D98 (40.8 Gy vs 44.5 Gy) were better with re-optimization and the differences were statistically significant (P < 0.05). The OARs doses for 0.5 cc, 1 cc, 5 cc and 10 cc were compared. The right and left sided lesions were analyzed separately. For the left sided metastases there was OARs dose violation for stomach in one patient and for bowel in one patient. For the right sided metastases there was OARs dose violation for duodenum in two patients and for bowel in two patients. After re-optimization all dosimetric parameters met the institutional constraints. Local control rate was 93.8% with a median follow up time of 11.7 months (range 4.5-26.4 months). One patient with progressive disease underwent adrenalectomy. All treatments were well tolerated. The most common radiation induced acute toxicities were grade 1-2 fatigue and nausea. There were no grade 3 or higher acute or late toxicities experienced during the treatment and follow-up course.The use of re-optimization with SMART improved the PTV coverage and OARs doses for treatment of adrenal metastases. SMART has some advantages when compared to other radiotherapy techniques due to its better visualization of soft tissue, real-time tumor tracking without fiducial markers and potentially reduced toxicity to OARs. These results need to be confirmed with more patients and longer follow-up.