Stereoscopic X-ray image and thermo-optical surface guidance for breast cancer radiotherapy in deep inspiration breath-hold.

PURPOSE: To investigate the feasibility of a thermo-optical surface imaging (SGRT) system combined with room-based stereoscopic X­ray image guidance (IGRT) in a dedicated breast deep inspiration breath-hold (DIBH) irradiation workflow. In this context, benchmarking of portal imaging (EPID) and cone-beam CT (CBCT) against stereoscopic X­rays was performed. METHODS: SGRT + IGRT data of 30 left-sided DIBH breast patients (1 patient with bilateral cancer) treated in 351 fractions using thermo-optical surface imaging and X-ray IGRT were retrospectively analysed. Patients were prepositioned based on a free-breathing surface reference derived from a CT scan. Once the DIBH was reached using visual feedback, two stereoscopic X­ray images were acquired and registered to the digitally reconstructed radiographs derived from the DIBH CT. Based on this registration, a couch correction was performed. Positioning and monitoring by surface and X-ray imaging were verified by protocol-based EPID or CBCT imaging at selected fractions and the calculation of residual geometric deviations. RESULTS: The median X­ray-derived couch correction vector was 4.9 (interquartile range [IQR] 3.3-7.1) mm long. Verification imaging was performed for 134 fractions (216 RT field verifications) with EPID and for 37 fractions with CBCT, respectively. The median 2D/3D deviation vector length over all verification images was 2.5 (IQR 1.6-3.9) mm/3.4 (IQR 2.2-4.8) mm for EPID/CBCT, both being well within the planning target volume (PTV) margins (7 mm). A moderate correlation (0.49-0.65) was observed between the surface signal and X-ray position in DIBH. CONCLUSION: DIBH treatments using thermo-optical SGRT and X-ray IGRT were feasible for breast cancer patients. Stereoscopic X­ray positioning was successfully verified by standard IGRT techniques.

Early morbidity and dose-volume effects in definitive radiochemotherapy for locally advanced cervical cancer: a prospective cohort study covering modern treatment techniques.

PURPOSE: Predicting morbidity for patients with locally advanced cervix cancer after external beam radiotherapy (EBRT) based on dose-volume parameters remains an unresolved issue in definitive radiochemotherapy. The aim of this prospective study was to correlate patient characteristics and dose-volume parameters to various early morbidity endpoints for different EBRT techniques, including volumetric modulated arc therapy (VMAT) and adaptive radiotherapy (ART). METHODS AND MATERIALS: The study population consisted of 48 patients diagnosed with locally advanced cervix cancer, treated with definitive radiochemotherapy including image-guided adaptive brachytherapy (IGABT). Multiple questionnaires (CTCAE 4.03, QLQ-C30 and EORTC QLQ-CX24) were assessed prospectively for patients treated with different EBRT techniques, including online adaptive VMAT. Contouring and treatment planning was based on the EMBRACE protocols. Acute toxicity, classified as general, gastrointestinal (GI) or genitourinary (GU) and their corresponding dose-volume histograms (DVHs) were first correlated by applying least absolute shrinkage and selection operator (LASSO) and subsequently evaluated by multiple logistic binomial regression. RESULTS: The treated EBRT volumes varied for the different techniques with ~2500 cm3 for 3D conformal radiotherapy (3D-CRT), ~2000 cm3 for EMBRACE­I VMAT, and ~1800 cm3 for EMBRACE-II VMAT and ART. In general, a worsening of symptoms during the first 5 treatment weeks and recovery afterwards was observed. Dose-volume parameters significantly correlating with stool urgency, rectal and urinary incontinence were as follows: bowel V40Gy < 250 cm3, rectum V40Gy < 80% and bladder V40Gy < 80-90%. CONCLUSION: This prospective study demonstrated the impact of EBRT treatment techniques in combination with chemotherapy on early morbidity. Dose-volume effects for dysuria, urinary incontinence, stool urgency, diarrhea, rectal bleeding, rectal incontinence and weight loss were found.

Automated volumetric modulated arc therapy planning for whole pelvic prostate radiotherapy.

BACKGROUND: For several tumor entities, automated treatment planning has improved plan quality and planning efficiency, and may enable adaptive treatment approaches. Whole-pelvic prostate radiotherapy (WPRT) involves large concave target volumes, which present a challenge for volumetric arc therapy (VMAT) optimization. This study evaluates automated VMAT planning for WPRT-VMAT and compares the results with manual expert planning. METHODS: A system for fully automated multi-criterial plan generation was configured for each step of sequential-boost WPRT-VMAT, with final "autoVMAT" plans being automatically calculated by the Monaco treatment planning system (TPS; Elekta AB, Stockholm, Sweden). Configuration was based on manually generated VMAT plans (manualVMAT) of 5 test patients, the planning protocol, and discussions with the treating physician on wishes for plan improvements. AutoVMAT plans were then generated for another 30 evaluation patients and compared to manualVMAT plans. For all 35 patients, manualVMAT plans were optimized by expert planners using the Monaco TPS. RESULTS: AutoVMAT plans exhibited strongly improved organ sparing and higher conformity compared to manualVMAT. On average, mean doses (Dmean) of bladder and rectum were reduced by 10.7 and 4.5 Gy, respectively, by autoVMAT. Prostate target coverage (V95%) was slightly higher (+0.6%) with manualVMAT. In a blinded scoring session, the radiation oncologist preferred autoVMAT plans to manualVMAT plans for 27/30 patients. All treatment plans were considered clinically acceptable. The workload per patient was reduced by > 70 min. CONCLUSION: Automated VMAT planning for complex WPRT dose distributions is feasible and creates treatment plans that are generally dosimetrically superior to manually optimized plans.

Tailoring the Mass Density of 3D Printing Materials for Accurate X-ray Imaging Simulation by Controlled Underfilling for Radiographic Phantoms.

Additive manufacturing and 3D printing allow for the design and rapid production of radiographic phantoms for X-ray imaging, including CT. These are used for numerous purposes, such as patient simulation, optimization of imaging procedures and dose levels, system evaluation and quality assurance. However, standard 3D printing polymers do not mimic X-ray attenuation properties of tissues like soft, adipose, lung or bone tissue, and standard materials like liquid water. The mass density of printing polymers-especially important in CT-is often inappropriate, i.e., mostly too high. Different methods can be applied to reduce mass density. This work examines reducing density by controlled underfilling either realized by using 3D printing materials expanded through foaming during heating in the printing process, or reducing polymer flow to introduce microscopic air-filled voids. The achievable density reduction depends on the base polymer used. When using foaming materials, density is controlled by the extrusion temperature, and ranges from 33 to 47% of the base polymer used, corresponding to a range of -650 to -394 HU in CT with 120 kV. Standard filaments (Nylon, modified PLA and modified ABS) allowed density reductions by 20 to 25%, covering HU values in CT from -260 to 77 (Nylon), -230 to -20 (ABS) and -81 to 143 (PLA). A standard chalk-filled PLA filament allowed reproduction of bone tissue in a wide range of bone mineral content resulting in CT numbers from 57 to 460 HU. Controlled underfilling allowed the production of radiographic phantom materials with continuously adjustable attenuation in a limited but appropriate range, allowing for the reproduction of X-ray attenuation properties of water, adipose, soft, lung, and bone tissue in an accurate, predictable and reproducible manner.

Explicitly encoding the cyclic nature of breathing signal allows for accurate breathing motion prediction in radiotherapy with minimal training data.

Background and purpose: Active breathing motion management in radiotherapy consists of motion monitoring, quantification and mitigation. It is impacted by associated latencies of a few 100 ms. Artificial neural networks can successfully predict breathing motion and eliminate latencies. However, they require usually a large dataset for training. The objective of this work was to demonstrate that explicitly encoding the cyclic nature of the breathing signal into the training data enables significant reduction of training datasets which can be obtained from healthy volunteers. Material and methods: Seventy surface scanner breathing signals from 25 healthy volunteers in anterior-posterior direction were used for training and validation (ratio 4:1) of long short-term memory models. The model performance was compared to a model using decomposition into phase, amplitude and a time-dependent baseline. Testing of the models was performed on 55 independent breathing signals in anterior-posterior direction from surface scanner (35 lung, 20 liver) of 30 patients with a mean breathing amplitude of (5.9 ± 6.7) mm. Results: Using the decomposed breathing signal allowed for a reduction of the absolute root-mean square error (RMSE) from 0.34 mm to 0.12 mm during validation. Testing using patient data yielded an average absolute RMSE of the breathing signal of (0.16 ± 0.11) mm with a prediction horizon of 500 ms. Conclusion: It was demonstrated that a motion prediction model can be trained with less than 100 datasets of healthy volunteers if breathing cycle parameters are considered. Applied to 55 patients, the model predicted breathing motion with a high accuracy.

Silicone phantoms fabricated with multi-material extrusion 3D printing technology mimicking imaging properties of soft tissues in CT.

Recently, 3D printing has been widely used to fabricate medical imaging phantoms. So far, various rigid 3D printable materials have been investigated for their radiological properties and efficiency in imaging phantom fabrication. However, flexible, soft tissue materials are also needed for imaging phantoms for simulating several clinical scenarios where anatomical deformations is important. Recently, various additive manufacturing technologies have been used to produce anatomical models based on extrusion techniques that allow the fabrication of soft tissue materials. To date, there is no systematic study in the literature investigating the radiological properties of silicone rubber materials/fluids for imaging phantoms fabricated directly by extrusion using 3D printing techniques. The aim of this study was to investigate the radiological properties of 3D printed phantoms made of silicone in CT imaging. To achieve this goal, the radiodensity as described as Hounsfield Units (HUs) of several samples composed of three different silicone printing materials were evaluated by changing the infill density to adjust their radiological properties. A comparison of HU values with a Gammex Tissue Characterization Phantom was performed. In addition, a reproducibility analysis was performed by creating several replicas for specific infill densities. A scaled down anatomical model derived from an abdominal CT was also fabricated and the resulting HU values were evaluated. For the three different silicone materials, a spectrum ranging from -639 to +780 HU was obtained on CT at a scan setting of 120 kVp. In addition, using different infill densities, the printed materials were able to achieve a similar radiodensity range as obtained in different tissue-equivalent inserts in the Gammex phantom (238 HU to -673 HU). The reproducibility results showed good agreement between the HU values of the replicas compared to the original samples, confirming the reproducibility of the printed materials. A good agreement was observed between the HU target values in abdominal CT and the HU values of the 3D-printed anatomical phantom in all tissues.

Additively manufactured test phantoms for mimicking soft tissue radiation attenuation in CBCT using Polyjet technology.

OBJECTIVES: To develop and validate a simple approach for building cost-effective imaging phantoms for Cone Beam Computed Tomography (CBCT) using a modified Polyjet additive manufacturing technology where a single material can mimic a range of human soft-tissue radiation attenuation. MATERIALS AND METHODS: Single material test phantoms using a cubic lattice were designed in 3-Matic 15.0 software . Keeping the individual cubic lattice volume constant, eight different percentage ratio (R) of air: material from 0% to 70% with a 10% increment were assigned to each sample. The phantoms were printed in three materials, namely Vero PureWhite, VeroClear and TangoPlus using Polyjet technology. The CT value analysis, non-contact profile measurement and microCT-based volumetric analysis was performed for all the samples. RESULTS: The printed test phantoms produced a grey value spectrum equivalent to the radiation attenuation of human soft tissues in the range of -757 to +286 HU on CT. The results from dimensional comparison analysis of the printed phantoms with the digital test phantoms using non-contact profile measurement showed a mean accuracy of 99.07 % and that of micro-CT volumetric analysis showed mean volumetric accuracy of 84.80-94.91%. The material and printing costs of developing 24 test phantoms was 83.00 Euro. CONCLUSIONS: The study shows that additive manufacturing-guided macrostructure manipulation modifies successfully the radiographic visibility of a material in CBCT imaging with 1 mm3 resolution, helping customization of imaging phantoms.

3D-Printed multi-material liver model with simultaneous mechanical and radiological tissue-mimicking features for improved realism.

89Anatomic models have an important role in the medical domain. However, soft tissue mechanical properties' representation is limited in mass-produced and 3D-printed models. In this study, a multi-material 3D printer was used to print a human liver model featuring tuned mechanical and radiological properties, with the goal of comparing the printed model with its printing material and real liver tissue. The main target was mechanical realism, while radiological similarity was a secondary objective. Materials and internal structure were selected such that the printed model would resemble liver tissue in terms of tensile properties. The model was printed at 33% scaling and 40% gyroid infill with a soft silicone rubber, and silicone oil as a filler fluid. After printing, the liver model underwent CT scanning. Since the shape of the liver is incompatible with tensile testing, tensile testing specimens were also printed. Three replicates were printed with the same internal structure as the liver model and three more out of silicone rubber with 100% rectilinear infill to allow a comparison. All specimens were tested in a four-step cyclic loading test protocol to compare elastic moduli and dissipated energy ratios. The fluid-filled and full-silicone specimens had initial elastic moduli of 0.26 MPa and 0.37 MPa, respectively, and featured dissipated energy ratios of 0.140, 0.167, 0.183, and 0.118, 0.093, 0.081, respectively, in the second, third, and fourth loading cycles. The liver model showed 225 ± 30 Hounsfield units (HU) in CT, which is closer to real human liver (70 ± 30 HU) than the printing silicone (340 ± 50 HU). Results suggest that the liver model became more realistic in terms of mechanical and radiological properties with the proposed printing approach as opposed to printing only with silicone rubber. Thus, it has been demonstrated that this printing method enables new customization opportunities in the field of anatomic models.

Clinical Implementation and Evaluation of Auto-Segmentation Tools for Multi-Site Contouring in Radiotherapy.

Background and purpose: Tools for auto-segmentation in radiotherapy are widely available, but guidelines for clinical implementation are missing. The goal was to develop a workflow for performance evaluation of three commercial auto-segmentation tools to select one candidate for clinical implementation. Materials and Methods: One hundred patients with six treatment sites (brain, head-and-neck, thorax, abdomen, and pelvis) were included. Three sets of AI-based contours for organs-at-risk (OAR) generated by three software tools and manually drawn expert contours were blindly rated for contouring accuracy. The dice similarity coefficient (DSC), the Hausdorff distance, and a dose/volume evaluation based on the recalculation of the original treatment plan were assessed. Statistically significant differences were tested using the Kruskal-Wallis test and the post-hoc Dunn Test with Bonferroni correction. Results: The mean DSC scores compared to expert contours for all OARs combined were 0.80 ± 0.10, 0.75 ± 0.10, and 0.74 ± 0.11 for the three software tools. Physicians' rating identified equivalent or superior performance of some AI-based contours in head (eye, lens, optic nerve, brain, chiasm), thorax (e.g., heart and lungs), and pelvis and abdomen (e.g., kidney, femoral head) compared to manual contours. For some OARs, the AI models provided results requiring only minor corrections. Bowel-bag and stomach were not fit for direct use. During the interdisciplinary discussion, the physicians' rating was considered the most relevant. Conclusion: A comprehensive method for evaluation and clinical implementation of commercially available auto-segmentation software was developed. The in-depth analysis yielded clear instructions for clinical use within the radiotherapy department.

X-ray attenuation of bone, soft and adipose tissue in CT from 70 to 140 kV and comparison with 3D printable additive manufacturing materials.

Additive manufacturing and 3D printing are widely used in medical imaging to produce phantoms for image quality optimization, imaging protocol definition, comparison of image quality between different imaging systems, dosimetry, and quality control. Anthropomorphic phantoms mimic tissues and contrasts in real patients with regard to X-ray attenuation, as well as dependence on X-ray spectra. If used with different X-ray energies, or to optimize the spectrum for a certain procedure, the energy dependence of the attenuation must replicate the corresponding energy dependence of the tissues mimicked, or at least be similar. In the latter case the materials' Hounsfield values need to be known exactly to allow to correct contrast and contrast to noise ratios accordingly for different beam energies. Fresh bovine and porcine tissues including soft and adipose tissues, and hard tissues from soft spongious bone to cortical bone were scanned at different energies, and reference values of attenuation in Hounsfield units (HU) determined. Mathematical model equations describing CT number dependence on kV for bones of arbitrary density, and for adipose tissues are derived. These data can be used to select appropriate phantom constituents, compare CT values with arbitrary phantom materials, and calculate correction factors for phantoms consisting of materials with an energy dependence different to the tissues. Using data on a wide number of additive manufacturing and 3D printing materials, CT numbers and their energy dependence were compared to those of the tissues. Two commercially available printing filaments containing calcium carbonate powder imitate bone tissues with high accuracy at all kV values. Average adipose tissue can be duplicated by several off-the-shelf printing polymers. Since suitable printing materials typically exhibit a too high density for the desired attenuation of especially soft tissues, controlled density reduction by underfilling might improve tissue equivalence.

How to dose-stage large or high-risk brain metastases: an alternative two-fraction radiosurgical treatment approach.

OBJECTIVE: The authors sought to evaluate clinical outcome in patients with large, high-risk brain metastases (BMs) treated with different dose strategies by use of two-fraction dose-staged Gamma Knife radiosurgery (GKRS). METHODS: A retrospective analysis was performed with data from 142 patients from two centers who had been treated with two-fraction dose-staged GKRS between June 2015 and January 2020. Depending on the changes in marginal dose between the first (GKRS1) and second (GKRS2) GKRS treatments, the study population was divided into three treatment groups: dose escalation, dose maintenance, and dose de-escalation. RESULTS: The 142 study patients underwent two-fraction dose-staged GKRS treatments for 166 large, high-risk BMs. The median tumor volume of 7.4 cm3 decreased significantly from GKRS1 to GKRS2 (4.4 cm3; p < 0.001), and to the last follow-up (1.8 cm3; p < 0.001). These significant differences in BM volume reduction were achieved in all three treatment groups. However, differences according to the primary tumor histology were apparent: while dose maintenance seemed to be the most effective treatment strategy for BMs from lung cancer or melanoma, dose escalation was the most beneficial treatment option for BMs from breast, gastrointestinal, or genitourinary cancer. Of note, the vast majority of patients who underwent dose-staged BM treatment did not show any significant postradiosurgical complications. CONCLUSIONS: In patients with large, high-risk BMs, dose-staged GKRS treatment represents an effective local treatment method with acceptable complication risks. Different dose-strategy options are available that may be chosen according to the primary tumor histology and treatment volume but may also be tailored to the findings at GKRS2.

3D printed patient-specific thorax phantom with realistic heterogenous bone radiopacity using filament printer technology.

Current medical imaging phantoms are usually limited by simplified geometry and radiographic skeletal homogeneity, which confines their usage for image quality assessment. In order to fabricate realistic imaging phantoms, replication of the entire tissue morphology and the associated CT numbers, defined as Hounsfield Unit (HU) is required. 3D printing is a promising technology for the production of medical imaging phantoms with accurate anatomical replication. So far, the majority of the imaging phantoms using 3D printing technologies tried to mimic the average HU of soft tissue human organs. One important aspect of the anthropomorphic imaging phantoms is also the replication of realistic radiodensities for bone tissues. In this study, we used filament printing technology to develop a CT-derived 3D printed thorax phantom with realistic bone-equivalent radiodensity using only one single commercially available filament. The generated thorax phantom geometry closely resembles a patient and includes direct manufacturing of bone structures while creating life-like heterogeneity within bone tissues. A HU analysis as well as a physical dimensional comparison were performed in order to evaluate the density and geometry agreement between the proposed phantom and the corresponding CT data. With the achieved density range (-482 to 968 HU) we could successfully mimic the realistic radiodensity of the bone marrow as well as the cortical bone for the ribs, vertebral body and dorsal vertebral column in the thorax skeleton. In addition, considering the large radiodensity range achieved a full thorax imaging phantom mimicking also soft tissues can become feasible. The physical dimensional comparison using both Extrema Analysis and Collision Detection methods confirmed a mean surface overlap of 90% and a mean volumetric overlap of 84,56% between the patient and phantom model. Furthermore, the reproducibility analyses revealed a good geometry and radiodensity duplicability in 24 printed cylinder replicas. Thus, according to our results, the proposed additively manufactured anthropomorphic thorax phantom has the potential to be efficiently used for validation of imaging- and radiation-based procedures in precision medicine.

Classification of X-Ray Attenuation Properties of Additive Manufacturing and 3D Printing Materials Using Computed Tomography From 70 to 140 kVp.

Additive manufacturing and 3D printing is particularly useful in the production of phantoms for medical imaging applications including determination and optimization of (diagnostic) image quality and dosimetry. Additive manufacturing allows the leap from simple slab and stylized to (pseudo)-anthropomorphic phantoms. This necessitates the use of materials with x-ray attenuation as close as possible to that of the tissues or organs mimicked. X-ray attenuation properties including their energy dependence were determined for 35 printing materials comprising photocured resins and thermoplastic polymers. Prior to measuring x-ray attenuation in CT from 70 to 140 kVp, printing parameters were thoroughly optimized to ensure maximum density avoiding too low attenuation due to microscopic or macroscopic voids. These optimized parameters are made available. CT scanning was performed in a water filled phantom to guarantee defined scan conditions and accurate HU value determination. The spectrum of HU values covered by polymers printed using fused deposition modeling reached from -258 to +1,063 at 120 kVp (-197 to +1,804 at 70 kVp, to -266 to +985 at 140 kVp, respectively). Photocured resins covered 43 to 175 HU at 120 kVp (16-156 at 70, and 57-178 at 140 kVp). At 120 kVp, ASA mimics water almost perfectly (+2 HU). HIPS (-40 HU) is found close to adipose tissue. In all photocurable resins, and 17 printing filaments HU values decreased with increasing beam hardness contrary to soft tissues except adipose tissue making it difficult to mimic water or average soft tissue in phantoms correctly over a range of energies with one single printing material. Filled filaments provided both, the HU range, and an appropriate energy dependence mimicking bone tissues. A filled material with almost constant HU values was identified potentially allowing mimicking soft tissues by reducing density using controlled under-filling. The measurements performed in this study can be used to design phantoms with a wide range of x-ray contrasts, and energy dependence of these contrasts by combining appropriate materials. Data provided on the energy dependence can also be used to correct contrast or contrast to noise ratios from phantom measurements to real tissue contrasts or CNRs.

Toward on-the-fly trajectory optimization for C-arm CBCT under strong kinematic constraints.

Cone beam computed tomography (CBCT) has become a vital tool in interventional radiology. Usually, a circular source-detector trajectory is used to acquire a three-dimensional (3D) image. Kinematic constraints due to the patient size or additional medical equipment often cause collisions with the imager while performing a full circular rotation. In a previous study, we developed a framework to design collision-free, patient-specific trajectories for the cases in which circular CBCT is not feasible. Our proposed trajectories included enough information to appropriately reconstruct a particular volume of interest (VOI), but the constraints had to be defined before the intervention. As most collisions are unpredictable, performing an on-the-fly trajectory optimization is desirable. In this study, we propose a search strategy that explores a set of trajectories that cover the whole collision-free area and subsequently performs a search locally in the areas with the highest image quality. Selecting the best trajectories is performed using simulations on a prior diagnostic CT volume which serves as a digital phantom for simulations. In our simulations, the Feature SIMilarity Index (FSIM) is used as the objective function to evaluate the imaging quality provided by different trajectories. We investigated the performance of our methods using three different anatomical targets inside the Alderson-Rando phantom. We used FSIM and Universal Quality Image (UQI) to evaluate the final reconstruction results. Our experiments showed that our proposed trajectories could achieve a comparable image quality in the VOI compared to the standard C-arm circular CBCT. We achieved a relative deviation less than 10% for both FSIM and UQI metrics between the reconstructed images from the optimized trajectories and the standard C-arm CBCT for all three targets. The whole trajectory optimization took approximately three to four minutes.

An MR-only acquisition and artificial intelligence based image-processing protocol for photon and proton therapy using a low field MR.

OBJECTIVE: Recent developments on synthetically generated CTs (sCT), hybrid MRI linacs and MR-only simulations underlined the clinical feasibility and acceptance of MR guided radiation therapy. However, considering clinical application of open and low field MR with a limited field of view can result in truncation of the patient's anatomy which further affects the MR to sCT conversion. In this study an acquisition protocol and subsequent MR image stitching is proposed to overcome the limited field of view restriction of open MR scanners, for MR-only photon and proton therapy. MATERIAL AND METHODS: 12 prostate cancer patients scanned with an open 0.35T scanner were included. To obtain the full body contour an enhanced imaging protocol including two repeated scans after bilateral table movement was introduced. All required structures (patient contour, target and organ at risk) were delineated on a post-processed combined transversal image set (stitched MRI). The postprocessed MR was converted into a sCT by a pretrained neural network generator. Inversely planned photon and proton plans (VMAT and SFUD) were designed using the sCT and recalculated for rigidly and deformably registered CT images and compared based on D2%, D50%, V70Gy for organs at risk and based on D2%, D50%, D98% for the CTV and PTV. The stitched MRI and the untruncated MRI were compared to the CT, and the maximum surface distance was calculated. The sCT was evaluated with respect to delineation accuracy by comparing on stitched MRI and sCT using the DICE coefficient for femoral bones and the whole body. RESULTS: Maximum surface distance analysis revealed uncertainties in lateral direction of 1-3mm on average. DICE coefficient analysis confirms good performance of the sCT conversion, i.e. 92%, 93%, and 100% were obtained for femoral bone left and right and whole body. Dose comparison resulted in uncertainties below 1% between deformed CT and sCT and below 2% between rigidly registered CT and sCT in the CTV for photon and proton treatment plans. DISCUSSION: A newly developed acquisition protocol for open MR scanners and subsequent Sct generation revealed good acceptance for photon and proton therapy. Moreover, this protocol tackles the restriction of the limited FOVs and expands the capacities towards MR guided proton therapy with horizontal beam lines.

Additively Manufactured Patient-Specific Anthropomorphic Thorax Phantom With Realistic Radiation Attenuation Properties.

Conventional medical imaging phantoms are limited by simplified geometry and radiographic skeletal homogeneity, which confines their usability for image quality assessment and radiation dosimetry. These challenges can be addressed by additive manufacturing technology, colloquially called 3D printing, which provides accurate anatomical replication and flexibility in material manipulation. In this study, we used Computed Tomography (CT)-based modified PolyJetTM 3D printing technology to print a hollow thorax phantom simulating skeletal morphology of the patient. To achieve realistic heterogenous skeletal radiation attenuation, we developed a novel radiopaque amalgamate constituting of epoxy, polypropylene and bone meal powder in twelve different ratios. We performed CT analysis for quantification of material radiodensity (in Hounsfield Units, HU) and for identification of specific compositions corresponding to the various skeletal structures in the thorax. We filled the skeletal structures with their respective radiopaque amalgamates. The phantom and isolated 3D printed rib specimens were rescanned by CT for reproducibility tests regarding verification of radiodensity and geometry. Our results showed that structural densities in the range of 42-705HU could be achieved. The radiodensity of the reconstructed phantom was comparable to the three skeletal structures investigated in a real patient thorax CT: ribs, ventral vertebral body and dorsal vertebral body. Reproducibility tests based on physical dimensional comparison between the patient and phantom CT-based segmentation displayed 97% of overlap in the range of 0.00-4.57 mm embracing the anatomical accuracy. Thus, the additively manufactured anthropomorphic thorax phantom opens new vistas for imaging- and radiation-based patient care in precision medicine.

Optimization for customized trajectories in cone beam computed tomography.

PURPOSE: We developed a target-based cone beam computed tomography (CBCT) imaging framework for optimizing an unconstrained three dimensional (3D) source-detector trajectory by incorporating prior image information. Our main aim is to enable a CBCT system to provide topical information about the target using a limited angle noncircular scan orbit with a minimal number of projections. Such a customized trajectory should include enough information to sufficiently reconstruct a particular volume of interest (VOI) under kinematic constraints, which may result from the patient size or additional surgical or radiation therapy-related equipment. METHODS: A patient-specific model from a prior diagnostic computed tomography (CT) volume is used as a digital phantom for CBCT trajectory simulations. Selection of the best projection views is accomplished through maximizing an objective function fed by the imaging quality provided by different x-ray positions on the digital phantom data. The final optimized trajectory includes a limited angular range and a minimal number of projections which can be applied to a C-arm device capable of general source-detector positioning. The performance of the proposed framework is investigated in experiments involving an in-house-built box phantom including spherical targets as well as an Alderson-Rando head phantom. In order to quantify the image quality of the reconstructed image, we use the average full-width-half-maximum (FWHMavg ) for the spherical target and feature similarity index (FSIM), universal quality index (UQI), and contrast-to-noise ratio (CNR) for an anatomical target. RESULTS: Our experiments based on both the box and head phantom showed that optimized trajectories could achieve a comparable image quality in the VOI with respect to the standard C-arm circular CBCT while using approximately one quarter of projections. We achieved a relative deviation <7% for FWHMavg between the reconstructed images from the optimized trajectories and the standard C-arm CBCT for all spherical targets. Furthermore, for the anatomical target, the relative deviation of FSIM, UQI, and CNR between the reconstructed image related to the proposed trajectory and the standard C-arm circular CBCT was found to be 5.06%, 6.89%, and 8.64%, respectively. We also compared our proposed trajectories to circular trajectories with equivalent angular sampling as the optimized trajectories. Our results show that optimized trajectories can outperform simple partial circular trajectories in the VOI in term of image quality. Typically, an angular range between 116° and 152° was used for the optimized trajectories. CONCLUSION: We demonstrated that applying limited angle noncircular trajectories with optimized orientations in 3D space can provide a suitable image quality for particular image targets and has a potential for limited angle and low-dose CBCT-based interventions under strong spatial constraints.

Image guided adaptive external beam radiation therapy for cervix cancer: Evaluation of a clinically implemented plan-of-the-day technique.

BACKGROUND: Radiotherapy for cervix cancer is challenging in patients exhibiting large daily changes in the pelvic anatomy, therefore adaptive treatments (ART) have been proposed. The aim of this study was the clinical implementation and subsequent evaluation of plan-of-the-day (POTD)-ART for cervix cancer in supine positioning. The described workflow was based on standard commercial equipment and current quality assurance (QA) methods. MATERIALS AND METHODS: A POTD strategy, which employs a VMAT plan library consisting of an empty bladder plan, a full bladder plan and a motion robust backup plan, was developed. Daily adaption was guided by cone beam computed tomography (CBCT) imaging after which the best plan from the library was selected. Sixteen patients were recruited in a clinical study on ART, for nine POTD was applied due to their large organ motion derived from two computed tomography (CT) scans with variable bladder filling. All patients were treated to 45Gy in 25 fractions. Plan selection frequencies over the treatment course were analyzed. Daily doses in the rectum, bladder and cervix-uterus target (CTV-T) were derived and compared to a simulated non-adapted treatment (non-ART), which employed the robust plan for each fraction. Additionally, the adaption consistency was determined by repeating the plan selection procedure one month after treatment by a group of experts. ART-specific QA methods are presented. RESULTS: 225 ART fractions with CBCTs were analyzed. The empty bladder plan was delivered in 49% of the fractions in the first treatment week and this number increased to 78% in the fifth week. The daily coverage of the CTV-T was equivalent between ART and the non-ART simulation, while the daily total irradiated volume V42.75Gy (95% of prescription dose) was reduced by a median of 87cm3. The median delivered V42.75Gy was 1782cm3. Daily delivered doses (V42.75Gy, V40Gy, V30G) to the organs at risk were statistically significantly reduced by ART, with a median difference in daily V42.75Gy in rectum and bladder of 3.2% and 1.1%, respectively. The daily bladder V42.75Gy and V40Gy were decreased by more than 10 percent points in 30% and 24% of all fractions, respectively, through ART. The agreement between delivered plans and retrospective expert-group plan selections was 84%. CONCLUSION: A POTD-ART technique for cervix cancer was successfully and safely implemented in the clinic and evaluated. Improved normal tissue sparing compared to a simulated non-ART treatment could be demonstrated. Future developments should focus on commercial automated software solutions to allow for a more widespread adoption and to keep the increased workload manageable.

Advanced optimization methods for whole pelvic and local prostate external beam therapy.

PURPOSE: Radiation treatment planning inherently involves multiple conflicting planning goals, which makes it a suitable application for multicriteria optimization (MCO). This study investigates a MCO algorithm for VMAT planning (VMAT-MCO) for prostate cancer treatments including pelvic lymph nodes and uses standard inverse VMAT optimization (sVMAT) and Tomotherapy planning as benchmarks. METHODS: For each of ten prostate cancer patients, a two stage plan was generated, consisting of a stage 1 plan delivering 22Gy to the prostate, and a stage 2 plan delivering 50.4Gy to the lymph nodes and 56Gy to the prostate with a simultaneous integrated boost. The single plans were generated by three planning techniques (VMAT-MCO, sVMAT, Tomotherapy) and subsequently compared with respect to plan quality and planning time efficiency. RESULTS: Plan quality was similar for all techniques, but sVMAT showed slightly better rectum (on average Dmean -7%) and bowel sparing (Dmean -17%) compared to VMAT-MCO in the whole pelvic treatments. Tomotherapy plans exhibited higher bladder dose (Dmean +42%) in stage 1 and lower rectum dose (Dmean -6%) in stage 2 than VMAT-MCO. Compared to manual planning, the planning time with MCO was reduced up to 12 and 38min for stage 1 and 2 plans, respectively. CONCLUSION: MCO can generate highly conformal prostate VMAT plans with minimal workload in the settings of prostate-only treatments and prostate plus lymph nodes irradiation. In the whole pelvic plan manual VMAT optimization led to slightly improved OAR sparing over VMAT-MCO, whereas for the primary prostate treatment plan quality was equal.

Impact of organ shape variations on margin concepts for cervix cancer ART.

BACKGROUND AND PURPOSE: Target and organ movement motivate adaptive radiotherapy for cervix cancer patients. We investigated the dosimetric impact of margin concepts with different levels of complexity on both organ at risk (OAR) sparing and PTV coverage. MATERIAL AND METHODS: Weekly CT and daily CBCT scans were delineated for 10 patients. The dosimetric impact of organ shape variations were evaluated for four (isotropic) margin concepts: two static PTVs (PTV6mm and PTV15mm), a PTV based on ITV of the planning CT and CBCTs of the first treatment week (PTVART ITV) and an adaptive PTV based on a library approach (PTVART Library). RESULTS: Using static concepts, OAR doses increased with large margins, while smaller margins compromised target coverage. ART PTVs resulted in comparable target coverage and better sparing of bladder (V40Gy: 15% and 7% less), rectum (V40Gy: 18 and 6cc less) and bowel (V40Gy: 106 and 15cc less) compared to PTV15mm. Target coverage evaluation showed that for elective fields a static 5mm margin sufficed. CONCLUSION: PTVART Library achieved the best dosimetric results. However when weighing clinical benefit against workload, ITV margins based on repetitive movement evaluation during the first week also provide improvements over static margin concepts.