Reference Plan Research Articles

From Low to High Order Motion Planners: Safe Robot Navigation Using Motion Prediction and Reference Governor

Safe navigation around obstacles is a fundamental challenge for highly dynamic robots. The state-of-the-art approach for adapting simple reference path planners to complex robot dynamics using trajectory optimization and tracking control is brittle and requires significant replanning cycles. In this letter, we introduce a novel feedback motion planning framework that extends the applicability of low-order (e.g. position-/velocity-controlled) reference motion planners to high-order (e.g., acceleration-/jerk-controlled) robot models using motion prediction and reference governors. We use predicted robot motion range for safety assessment and establish a continuous bidirectional interface between high-level planning and low-level control via a reference governor. We describe the generic fundamental building blocks of our feedback motion planning framework and give specific example designs for motion control, prediction, and reference planning. We prove the correctness of our planning framework and demonstrate its performance in numerical simulations. We conclude that accurate motion prediction is crucial for closing the gap between high-level planning and low-level control.

The effect of respiration-induced target motion on 3D magnetic resonance images used to guide radiotherapy

3D Magnetic Resonance Imaging (MRI) is used in radiation therapy for reference planning and, lately, for adaptive treatments on MR accelerators. This study aimed to investigate the impact of different types of respiratory motion on the apparent target position and extent in such scans. An MRI motion phantom with a 30mm diameter target was used to simulate cranial-caudal (CC) motion and imaged at an MR-Linac using a standard clinically released 3D T2w sequence. Scans were acquired for each combination of functions (sin(t), sin4(t) and sin12(t)), peak-to-peak amplitudes(5, 10, 15 and 20mm), and periods (4, 5 and 6s). Furthermore, respiration CC motion patterns fromtwo patients were used. Motion functions were shifted such that the time average target position would match a static reference scan at 0-position. The target was automatically identified in coronal and sagittal images using k-means clustering. The mean position and area of the target were calculated and compared to the reference scan. Artefacts increased with amplitude and depended on the motion type. Sin(t) and sin4(t) oscillations resulted in a blurring of the target, which led to an increased target area, while sin12(t) motion did not show significant changes in the target area. However, for the sin12(t) motion, the offset in apparent position was prominent, while that was not the case for the sin(t) and sin4(t) motion. The patient respiration motion profiles showed similar trends. In 3D MRI, target motion can change apparent tumour extent and apparent position. The changes increase with motion amplitude and depend on the motion type.

OpenKBP-Opt: an international and reproducible evaluation of 76 knowledge-based planning pipelines

Objective. To establish an open framework for developing plan optimization models for knowledge-based planning (KBP). Approach. Our framework includes radiotherapy treatment data (i.e. reference plans) for 100 patients with head-and-neck cancer who were treated with intensity-modulated radiotherapy. That data also includes high-quality dose predictions from 19 KBP models that were developed by different research groups using out-of-sample data during the OpenKBP Grand Challenge. The dose predictions were input to four fluence-based dose mimicking models to form 76 unique KBP pipelines that generated 7600 plans (76 pipelines × 100 patients). The predictions and KBP-generated plans were compared to the reference plans via: the dose score, which is the average mean absolute voxel-by-voxel difference in dose; the deviation in dose-volume histogram (DVH) points; and the frequency of clinical planning criteria satisfaction. We also performed a theoretical investigation to justify our dose mimicking models. Main results. The range in rank order correlation of the dose score between predictions and their KBP pipelines was 0.50–0.62, which indicates that the quality of the predictions was generally positively correlated with the quality of the plans. Additionally, compared to the input predictions, the KBP-generated plans performed significantly better (P < 0.05; one-sided Wilcoxon test) on 18 of 23 DVH points. Similarly, each optimization model generated plans that satisfied a higher percentage of criteria than the reference plans, which satisfied 3.5% more criteria than the set of all dose predictions. Lastly, our theoretical investigation demonstrated that the dose mimicking models generated plans that are also optimal for an inverse planning model. Significance. This was the largest international effort to date for evaluating the combination of KBP prediction and optimization models. We found that the best performing models significantly outperformed the reference dose and dose predictions. In the interest of reproducibility, our data and code is freely available.

An economic model based on SkSP-2 with double sampling plan as the reference plan

Skip-lot sampling plans have been widely used in industries to reduce inspection efforts when products have excellent quality records. This paper provides an economic model based on SkSP-2 with the double sampling plan as a reference plan. The various combinations of producer quality level and consumer quality level by minimizing both the producer’s and the consumer’s risk have been discussed. Numerical examples are provided to confirm the application of the proposed concept.

Improving the clinical workflow of a MR-Linac by dosimetric evaluation of synthetic CT.

Adaptive radiotherapy performed on the daily magnetic resonance imaging (MRI) is an option to improve the treatment quality. In the adapt-to-shape workflow of 1.5-T MR-Linac, the contours of structures are adjusted on the basis of patient daily MRI, and the adapted plan is recalculated on the MRI-based synthetic computed tomography (syCT) generated by bulk density assignment. Because dosimetric accuracy of this strategy is a priority and requires evaluation, this study aims to explore the usefulness of adding an assessment of dosimetric errors associated with recalculation on syCT to the clinical workflow. Sixty-one patients, with various tumor sites, treated using a 1.5-T MR-Linac were included in this study. In Monaco V5.4, the target and organs at risk (OARs) were contoured, and a reference CT plan that contains information about the outlined contours, their average electron density (ED), and the priority of ED assignment was generated. To evaluate the dosimetric error of syCT caused by the inherent approximation within bulk density assignment, the reference CT plan was recalculated on the syCT obtained from the reference CT by forcing all contoured structures to their mean ED defined on the reference plan. The dose–volume histogram (DVH) and dose distribution of the CT and syCT plan were compared. The causes of dosimetric discrepancies were investigated, and the reference plan was reworked to minimize errors if needed. For 54 patients, gamma analysis of the dose distribution on syCT and CT show a median pass rate of 99.7% and 98.5% with the criteria of 3%/3 mm and 2%/2 mm, respectively. DVH difference of targets and OARs remained less than 1.5% or 1 Gy. For the remaining patients, factors (i.e., inappropriate ED assignments) influenced the dosimetric agreement of the syCT vs. CT reference DVH by up to 21%. The causes of the errors were promptly identified, and the DVH dosimetry was realigned except for two lung treatments for which a significant discrepancy remained. The recalculation on the syCT obtained from the planning CT is a powerful tool to assess and decrease the minimal error committed during the adaptive plan on the MRI-based syCT.

Evaluation and optimal designing of a two-level skip-lot sampling plan for resubmitted lots

In the quality management system, skip-lot sampling is a prominent beneficial sampling plan concerning the economic aspect since it requires minimum expenses for inspection. This study attempts to propose an innovative sampling plan by assimilating the concept of a resampling scheme in a two-level skip-lot sampling plan of type 3, that is, SkSP-2L.3, and the resultant plan is designated as SkSP-2L.3-R with a single sampling plan as the reference plan. Using Markov chain formulation, the performance measures are derived. The designing methodology is provided to determine the plan parameters of the SkSP-2L.3-R plan to minimize the average sample number by using two points on the operating characteristic curve approach. Tables are constructed to select the plan parameters under binomial distribution and Poisson distribution by considering various combinations of producer and consumer quality levels along with respective producer and consumer risks. An illustrative example is provided to depict the execution of the proposed SkSP-2L.3-R plan. The comparative study substantiates that the proposed SkSP-2L.3-R plan with a single sampling plan as the reference plan has outstanding performance than some other existing plans under binomial and Poisson distributions.

Dosimetric analysis of MR-LINAC treatment plans for salvage spine SBRT re-irradiation.

PurposeWe investigated the feasibility of thoracic spine stereotactic body radiotherapy (SBRT) using the Elekta Unity magnetic resonance‐guided linear accelerator (MRL) in patients who received prior radiotherapy. We hypothesized that Monaco treatment plans can improve the gross tumor volume minimum dose (GTVmin) with spinal cord preservation and maintain consistent plan quality during daily adaptation.MethodsPinnacle clinical plans for 10 patients who underwent thoracic spine SBRT (after prior radiotherapy) were regenerated in the Monaco treatment planning system for the Elekta Unity MRL using 9 and 13 intensity‐modulated radiotherapy (IMRT) beams. Monaco adapt‐to‐position (ATP) and adapt‐to‐shape (ATS) workflow plans were generated using magnetic resonance imaging with a simulated daily positional setup deviation, and these adaptive plans were compared with Monaco reference plans. Plan quality measures included target coverage, Paddick conformity index, gradient index, homogeneity index, spinal cord D0.01cc, esophagus D0.01cc, lung V10, and skin D0.01cc.ResultsGTVmin values from the Monaco 9‐beam and 13‐beam plans were significantly higher than those from Pinnacle plans (p < 0.01) with similar spinal cord dose. Spinal cord D0.01cc, esophagus D0.01cc, and lung V10 did not statistically differ among the three plans. The electron‐return effect did not induce remarkable dose effects around the lungs or skin. While in the ATP workflow, a large increase in GTVmin was observed at the cost of a 10%–50% increase in spinal cord D0.01cc, in the ATS workflow, the spinal cord dose increase was maintained within 3% of the reference plan.ConclusionThese findings show that MRL plans for thoracic spine SBRT are safe and feasible, allowing tumor dose escalation with spinal cord preservation and consistent daily plan adaptation using the ATS workflow. Careful plan review of hot spots and lung dose is necessary for safe MRL‐based treatment.

Benchmarking daily adaptation using fully automated radiotherapy treatment plan optimization for rectal cancer.

In daily plan adaptation the radiotherapy treatment plan is adjusted just prior to delivery. A simple approach is taking the planning objectives of the reference plan and directly applying these in re-optimization. Here we present a tested method to verify whether daily adaptation without tweaking of the objectives can maintain the plan quality throughout treatment. For fifteen rectal cancer patients, automated treatment planning was used to generate plans mimicking manual reference plans on the planning scans. For 74 fraction scans (4-5 per patient) an automated plan and a daily adapted plan were generated, where the latter re-optimizes the reference plan objectives without any tweaking. To evaluate the robustness of the daily adaptation, the adapted plans were compared to the autoplanning plans. Median differences between the autoplanning plans on the planning scans and the reference plans were between -1 and 0.2Gy. The largest interquartile range (1Gy) was seen for the Lumbar Skin D2%. For the daily scans the PTV D2% and D98% differences between autoplanning and adapted plans were within 0.7Gy, with mean differences within 0.3Gy. Positive differences indicate higher values were obtained using autoplanning. For the Bowelarea+Bladder and the Lumbar Skin the D2% and Dmean differences were all within 2.6Gy, with mean differences between -0.9 and 0.1Gy. Automated treatment planning can be used to benchmark daily adaptation techniques. The investigated adaptation workflow can robustly perform high quality adaptations without daily adjusting of the patient-specific planning objectives for rectal cancer radiotherapy.

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.

Conflict analysis and coordination mechanism of ESG Information Disclosure Based on GMCR under the background of double carbon target

In recent years, with the promotion of carbon peak and neutrality policy, the issue of environmental, social and governance (ESG) information disclosure has become a hot topic of common concern to all sectors of society. Through the study of the conflict mechanism in ESG information disclosure, it can help decision makers choose a solution which can be accepted by others and help them develop. By implementing the Graph Model for Conflict Resolution (GMCR), we construct a conflict model for governments, enterprises, financial institutions and investors in the ESG information disclosure. GMCR can conduct stability analysis based on their preferences, and reach equilibrium results so as to provide a worthy reference plan for multiple parties and build a coordinated development mechanism in which they can rely on and promote each other.

Efficiency optimized axial flow compressor stage with a given shape of flow-path

Performance improvement and optimization for Brayton cycle plants include mainly two aspects: one concerns thermodynamic cycle parameters, another concerns component parameters. As one aspect of the power plant optimizations, parameter optimization is an important design practice for performance improvement of axial flow compressor stage (AFCS). Stagnation isentropic efficiency (IEFF) optimization of AFCS is studied preliminarily by using 1-D flow theory. Optimization design model of AFCS with a given shape of flow-path is provided. Five parameters are taken as design variables, including absolute exit and inlet angles of rotor, absolute exit angle of stator, and relative air densities at exit and inlet stations of stator. Energy balance equations for 1-D flow are constraints. Analytical relations about stagnation IEFF and design variables of the AFCS are obtained. Numerical calculations are performed for a constant mean-diameter AFCS. The results illustrate influences of various fixed design parameters on the optimum stagnation IEFF of the AFCS. The results illustrate that optimal stagnation IEFFs with three fixed input parameter combinations of work coefficient and flow coefficient increase 0.78%, 5.15%, and 5.66% than that of reference plan, respectively; optimal stagnation IEFFs increases with increase of work coefficient and decrease of flow coefficient.

Assessing the Curve of Spee in Permanent Dentition in Class I, II, III Malocclusions and its Relation with Overjet and Overbite

Introduction: The curve of spee is very important in complete oral reconstructions and can be used as a reference for prosthetic and orthodontic reconstructions. This study assessed the curve of spee in the maxilla and mandible and its relationship with the overjet and overbite in class I, II, and III malocclusions in Iranian population. In this descriptive cross- sectional study, 75 pairs of dental casts with permanent dental system and having second molars, available in the clinic of Khorasgan Azad University and private orthodontic offices were selected and divided into three groups of 25 based on malocclusion I, II, and III.&#x0D; Materials &amp; Methods: In this descriptive cross- sectional study, 75 pairs of dental casts with permanent dental system and having second molars, available in the clinic of Khorasgan Azad University and private orthodontic offices were selected and divided into three groups of 25 based on malocclusion I, II and III. The radius and depth of curve of spee were obtained. Radius of the curve of spee, the tip of canine cusps, the mesiobuccal of the first molars, and the distobuccal cusps of the second molars were joined together in the form of an arch. To measure the depth of curve of spee, the reference plan was drawn from buccal canine cusp to distobuccal cusp of the second molars. The perpendicular lines were drawn from this line to the edge of the premolars cusp, the first molar and the second molar mesiobuccal cusp and the deepest part was regarded for the measurements. Overjet was measured as an average of 6 upper anterior teeth and overbite as an average of 4 anterior lower teeth and the values of radius and depth of horseshoe curvature and overbite and overjet values were analyzed by One-way ANOVA and Tukey test and Correlation between data was also examined by Pearson correlation coefficient test (p value = 0.05).&#x0D; Results: In class II malocclusion, overbite values had a significant relationship with radius (p value = 0.02) and depth of the curve of spee (p value = 0.04), in class III malocclusion, overbite values had a significant relationship with the curve of spee (p value = 0.001) had. In class II malocclusion, the curve of spee was deeper and overbite values were higher, and also in the class III malocclusions, a direct relationship existed between the curve of spee and overbite&#x0D; Conclusion: Curve of spee effects the values of overjet and overbite, and the presence of increased overbite results from a deep spee curvature.

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.

HISTORICAL URBAN ENVIRONMENT PRESERVATION MEASURES OF THE CITY AREAL

The article proposes the structuring of a set of measures aimed at protecting both individual monuments and objects, and the historical environment as a whole. The peculiarity of the monument protection approach to the historical area is the self-organization of the settlement, the environment is organized according to the level of elements - from individual objects to complexes and considers the historical area as an element of a more global urban environment. Once formed in the past, the structure of the historic city, is increasingly interfering, so the city loses its integrity. The city must fully comply with the new functions, so the processes of reconstruction taking place in it, changes in urban planning structure and the introduction of new elements are an integral part of development. Modern understanding of the monument essence dictates the need in preservation of its individual setting or in other words - the historical environment. The historical area is an instrument of historical environment’s urban protection, which provides: historic environment functions restoration; preservation of the historic environment functions; development of the historic environment functions. Within the historical areas, monument protection measures are reflected starting from the inventory of the monument resource, its further research, accounting, categorization and undoubtedly become the basis for determining the zoning of the area. The article describes the relationship between monument protection measures for the protection of the historical environment of habitats, as well as their division by the method of impact and the order of implementation. Thus, the first group includes basic practical measures - research, inventory, accounting, scientific study. The second group includes measures to ensure the systematization of objects - monitoring, integration, adaptation of monuments to modern life of the city, restoration and engineering protection of monuments. The third group includes mostly measures aimed at socialization, use and development of the historical environment - popularization, creation and formalization of protected areas. Groups of cultural heritage sites appear separately, for which monument protection concepts and legislation are poorly developed. The selected groups are clearly shown in the practical work on the creation of historical and architectural reference plans.

Design of static and dynamic ridge filters for FLASH-IMPT: A simulation study.

This paper focused on the design and optimization of ridge filter-based intensity-modulated proton therapy (IMPT), and its potential applications for FLASH. Differing from the standard pencil beam scanning (PBS) mode, no energy/layer switching is required and total treatment time can be shortened. Unique dose-influence matrices were generated as a proton beam traverses through slabs of different thicknesses (i.e., modulation by different layers). To establish the references for comparison, conventional IMPT plans (single field) were created using a large-scale nonlinear solver. The spot weights from the reference IMPT plans were used as inputs for optimizing the design of ridge filters. Two designs were evaluated: model A (static) and model B (dynamic). The ridge filter designs were first verified (by GEANT4 simulation) in a water phantom and then in an H&N case. A direct comparison was made between the GEANT4 simulation results of two models and their respective references, with regard to plan quality, dose-averaged dose rate, and total treatment time. In both the water phantom and the H&N case, two models are able to modulate dose distributions with high conformity, showing no significant difference relative to the reference plans. Dose rate-volume histograms suggest that in order to achieve a dose rate of 40Gy/s over 90% PTV, the beam intensity needs to be 2.5×1011 protons/s for both models. For a fraction dose of 10Gy, the total treatment time (including both irradiation time and dead time) can be shortened by a factor of 4.9 (model A) and 6.5 (model B), relative to the reference plans. Two proposed designs (both static and dynamic) can be used for PBS-IMPT requiring no layer switching. They are promising candidates for FLASH-IMPT capable of reducing treatment time and achieving high dose rates while maintaining dose conformity simultaneously.

A novel hierarchical predictive energy management strategy for plug-in hybrid electric bus combined with deep deterministic policy gradient

Energy management is a crucial technology to improve the energy economy of the plug-in hybrid electric bus (PHEB). This article proposes a novel hierarchical predictive energy management strategy combined with the deep deterministic policy gradient (DDPG) algorithm for superior energy economy performance and fast state of charge (SOC) reference planning of PHEB. In the upper layer, real velocity data collected from a fixed bus route are used to train the DDPG algorithm and the well-trained neural networks are extracted to plan the SOC reference trajectory efficiently before departure. In the lower layer, deep neural network (DNN) is employed to predict the velocity in a short term and a model predictive control (MPC) optimal controller is designed to allocate power flows optimally by tracking the SOC reference trajectory accurately. Simulation results show that the proposed strategy with high-efficiency SOC reference planning improves the energy economy by 4.32% compared with DDPG, and the energy economy achieves 98.61% of the global optimal algorithm. More importantly, the robustness and adaptiveness are validated in the case of imprecise velocity prediction and inaccurate pre-known driving cycles. This article contributes to the energy economy improvement for PHEBs through MPC and DDPG methods.

The cornea as a reference point in orthodontic diagnosing, a retrospective study.

The aim of the study is to provide scientific evidence on the possibility of using the Corneal point a skin point for measu-rements that can be made on both standard and three-dimensional photographs. Also, we want to demonstrate the stability of corneal point during the growth, to use it as a reference point. A sample of 105 radiographs was reached. A descriptive and longitudinal statistical analysis was performed. By data analysis we obtained more variability inter-subject of the millimetrically value of the SC plan. For this reason, we consi-dered the relationship between the SN and SC values and not a single value. In the cross-sectional study the T- test analysis did not show a different significant result of variations between SC and SN in both sexes; therefore, we considered these as unique sample. Longitudinal study has a major importance for to esta-blishing the age-related changes. By cross-selection and longitudinal analysis we obtained an overlapping trend of the SN and SC plan. As the SN plan has always been used as a reference plan for cephalometric measurements, although its variations in growth, it can be concluded that the SC plan can be considered equally a reference plan.

Clinical Implementation and Initial Experience With a 1.5 Tesla MR-Linac for MR-Guided Radiation Therapy for Gynecologic Cancer: An R-IDEAL Stage 1 and 2a First in Humans Feasibility Study of New Technology Implementation

PurposeMagnetic resonance imaging–guided linear accelerator systems (MR-linacs) can facilitate the daily adaptation of radiation therapy plans. Here, we report our early clinical experience using a MR-linac for adaptive radiation therapy of gynecologic malignancies. Methods and MaterialsTreatments were planned with an Elekta Monaco v5.4.01 and delivered by a 1.5 Tesla Elekta Unity MR-linac. The system offers a choice of daily adaptation based on either position (ATP) or shape (ATS) of the tumor and surrounding normal structures. The ATS approach has the option of manually editing the contours of tumors and surrounding normal structures before the plan is adapted. Here, we documented the duration of each treatment fraction; set-up variability (assessed by isocenter shifts in each plan) between fractions; and, for quality assurance, calculated the percentage of plans meeting the γ-criterion of 3%/3-mm distance to agreement. Deformable accumulated dose calculations were used to compare accumulated versus planned dose for patient treated with exclusively ATP fractions. ResultsOf the 10 patients treated with 90 fractions on the MR-linac, most received boost doses to recurrence in nodes or isolated tumors. Each treatment fraction lasted a median 32 minutes; fractions were shorter with ATP than with ATS (30 min vs 42 min, P < .0001). The γ criterion for all fraction plans exceeded >90% (median, 99.9%; range, 92.4%-100%; ie, all plans passed quality assurance testing). The average extent of isocenter shift was <0.5 cm in each axis. The accumulated dose to the gross tumor volume was within 5% of the reference plan for all ATP cases. Accumulated doses for lesions in the pelvic periphery were within <1% of the reference plan as opposed to –1.6% to –4.4% for central pelvic tumors. ConclusionsThe MR-linac is a reliable and clinically feasible tool for treating patients with gynecologic cancer.

The impact of target positioning error and tumor size on radiobiological parameters in robotic stereotactic radiosurgery for metastatic brain tumors.

This study aimed to evaluate the effect of target positioning error (TPE) on radiobiological parameters, such as tumor control probability (TCP) and normal tissue complication probability (NTCP), in stereotactic radiosurgery (SRS) for metastatic brain tumors of different sizes using CyberKnife. The reference SRS plans were created using the circular cone of the CyberKnife for each spherical gross tumor volume (GTV) with diameters (φ) of 5, 7.5, 10, 15, and 20mm, contoured on computed tomography images of the head phantom. Subsequently, plans involving TPE were created by shifting the beam center by 0.1-2.0mm in three dimensions relative to the reference plans using the same beam arrangements. Conformity index (CI), generalized equivalent uniform dose (gEUD)-based TCP, and NTCP of estimated brain necrosis were evaluated for each plan. When the gEUD parameter "a" was set to - 10, the CI and TCP for the reference plan at the φ5-mm GTV were 0.90 and 80.8%, respectively. The corresponding values for plans involving TPE of 0.5-mm, 1.0-mm, and 2.0-mm were 0.62 and 77.4%, 0.40 and 62.9%, and 0.12 and 7.2%, respectively. In contrast, the NTCP for all GTVs were the same. The TCP for the plans involving a TPE of 2-mm was 7.2% and 68.8% at the φ5-mm and φ20-mm GTV, respectively. The TPEs corresponding to a TCP reduction rate of 3% at the φ5-mm and φ20-mm GTV were 0.41 and 0.99mm, respectively. TPE had a significant effect on TCP in SRS for metastatic brain tumors using CyberKnife, particularly for small GTVs.

Predicting personalised and progressive adaptive dose escalation to gross tumour volume using knowledge-based planning models for inoperable advanced-stage non-small cell lung cancer patients treated with volumetric modulated arc therapy

Objectives. Increased radiation doses could improve local control and overall survival of lung cancer patients, however, this could be challenging without exceeding organs at risk (OAR) dose constraints, especially for patients with advanced-stage disease. Increasing OAR doses could reduce the therapeutic ratio and quality of life. It is therefore important to investigate methods to increase the dose to target volume without exceeding OAR dose constraints. Methods. Gross tumour volume (GTV) was contoured on synthetic computerised tomography (sCT) datasets produced using the Velocity adaptive radiotherapy software for eleven patients. The fractions where GTV volume decreased compared to that prior to radiotherapy (reference plan) were considered for personalised progressive dose escalation. The dose to the adapted GTV (GTVAdaptive) was increased until OAR doses were affected (as compared to the original clinical plan). Planning target volume (PTV) coverage was maintained for all plans. Doses were also escalated to the reference plan (GTVClinical) using the same method. Adapted, dose-escalated, plans were combined to estimate accumulated dose, D99 (dose to 99%) of GTVAdapted, PTV D99 and OAR doses and compared with those in the original clinical plans. Knowledge-based planning (KBP) model was developed to predict D99 of the adapted GTV with OAR doses and PTV coverage kept similar to the original clinical plans; prediction accuracy and model verification were performed using further data sets. Results. Compared to the original clinical plan, the dose to GTV was significantly increased without exceeding OAR doses. Adaptive dose-escalation increased the average D99 to GTVAdaptive by 15.1Gy and 8.7Gy compared to the clinical plans. The KBP models were verified and demonstrated prediction accuracy of 0.4% and 0.7% respectively. Conclusion. Progressive adaptive dose escalation can significantly increase the dose to GTV without increasing OAR doses or compromising the dose to microscopic disease. This may increase overall survival without increasing toxicities.