Patient Setup Research Articles

In silico study of the electronic portal imaging devices sensitivity to parotid glands shrinkage during radiotherapy for nasopharyngeal cases

This computational investigation examines the capability of electronic portal imaging devices (EPIDs) in detecting anatomical changes during radiation therapy. A photon beam for 6 MV was simulated using compliant phase-space files via BEAMnrc (an EGSnrc user code). Initially, the dose calculation was carried out using DOSXYZnrc, an EGSnrc user code, on a water-based calibration phantom made of water. Phantoms, constructed utilizing patient computed tomography data, were subsequently used to simulate clinically relevant parotid gland (PG) shrinkage through image deformation using ImSimQA software. Two EPID geometries were implemented; a simple water slab, and a comprehensive multi-layer representation of the EPID (referred to as the 17-slab model). Using a 1%/1 mm gamma index the 17-slab geometry was sensitive to volume reductions in the PG ≥ − 26% from its original volume, while the water slab detected volume reduction of ≥ − 28.5%. In a clinical setting, replanning of head and neck patients is initiated when a reduction of 24–30% in PG volume is detected through cone-beam computed tomography. The sensitivity index, indicative of the signal to error ratio between the reference and evaluated images, showed an increase as the gland volume decreased for both models. Notably, the 17-slab model consistently more sensitive than the water slab. This computational study highlights the prospective use of EPIDs in monitoring and detecting clinically significant volume changes in the PG during radiation treatment. Advances in knowledge: While EPIDs are frequently employed for patient setup and alignment, this computational work constructed a virtual EPID to assess its detection abilities for the anatomical changes in the PG due to radiation exposure in head and neck cancer cases.

Students training on virtual medical linear accelerator

At the Czech Technical University in Prague, we have installed virtual software environment simulating a radiotherapy treatment room with a medical linear accelerator (software VERT and VERT Physics by Vertual Ltd., United Kingdom). It is possible to simulate patient treatment and physics QA (quality assurance) measurements in virtual reality. This is beneficial for our students and teachers because there is no radiation present while doing the exercises and it is accessible at any time, unlike medical linear accelerators at hospitals. For our department, we have chosen the TrueBeam model by Varian Medical Systems, USA. The linear accelerator can be operated by the user in the same way as at the hospital, including the hardware pendant. There is a selection of patient treatment plans, CT images and RT structures, all of which can be visualised inside the treatment room, also during beam on, simulating the situation inside the patient while irradiating the tumour. Any DICOM files, even from another manufacturer’s linac (linear accelerator) or treatment planning system, can be imported into VERT. Apart from this, there is also an imaging interface and cone-beam CT interface showing options for patient setup. Another part of the software is a physics module with various phantoms and detectors for dosimetry as well as geometry tests. For example, a large water tank can be used for relative dosimetry of photon beams (percent depth doses and profiles), a smaller water phantom can be used for reference dosimetry or chamber cross calibration according to the TRS 398 (1) or IPEM (2) protocol. The results of measurements are based on look-up tables coming from real beam data, so dependence on the depth of measurement, field size, temperature and pressure and other parameters can be demonstrated. Moreover, it is possible to introduce many types of errors into the linac, such as jaw position, laser, or collimator miscalibration, and show how these errors propagate to patient irradiation and how they can be detected by QA tools. This paper is a short report on how this system has been used at our university and how it might be used in modern learning, pointing out its advantages and drawbacks. At the 16th Workshop on European Collaboration in Higher Education on Radiological and Nuclear Engineering and Radiation Protection (CHERNE) it was proposed that this virtual system could be used for an international student training course on medical physics in radiotherapy within the CHERNE network. This course might contain theoretical lectures with demonstrations on the virtual linac, practical exercises on the virtual linac and visits to hospitals (a photon radiotherapy centre, the Thomayer University Hospital in particular, and a proton therapy centre).

Setup and intra-fractional motion measurements using surface scanning in head and neck cancer radiotherapy– A feasibility study

Background and purposeSurface-guided radiotherapy (SGRT) is applied to improve patient set-up and to monitor intra-fraction motion. Head and neck cancer (H&N) patients are usually fixated using 5-point thermoplastic masks, that are experienced as uncomfortable or even stressful. Therefore, the feasibility of irradiating H&N patients without a mask by using SGRT was examined. Material and methodsNineteen H&N patients were included in a simulation study. Once a week, before the standard treatment, a maskless treatment was simulated, using SGRT for setup and intrafraction motion monitoring. Initial patient setup accuracy and intrafraction motion was determined using ConeBeam CT (CBCT) images as well as SGRT before and after the (simulated) treatment. The clinical target volume to planning target volume (CTV-PTV) margin for intrafraction motion was calculated. Using patient questionnaires, the patient-friendliness H&N irradiation with and without mask was determined. ResultsMaskless setup with SGRT and CBCT was as accurate as with a mask. SGRT showed that intrafraction motion was gradual during the treatment. The CTV-PTV margin correcting for intrafraction motion was 1.7 mm for maskless treatment without interventions, and 1.2 mm if corrected for motions > 2 mm. For 19 % of fractions, the intrafraction motion, as detected by both SGRT and CBCT, was larger than 2 mm in at least one direction. Sixteen patients preferred maskless treatment, while 3 worried they would move too much. ConclusionsUsing SGRT and a standard head rest resulted in a patient-friendly treatment with accurate patient setup and acceptably small intrafraction motion for H&N patients.

Optical Surface Management System and BladderScan for Patient Setup During Radiotherapy of Postoperative Prostate Cancer.

Background: The precision of postoperative prostate cancer radiotherapy is significantly influenced by setup errors and alterations in bladder morphology. Utilizing daily cone beam computed tomography (CBCT) imaging allows for the correction of setup errors. However, this naturally leads to the question of the issue of peripheral dose and workload. Thus, a zero-dose, noninvasive technique to reproduce the bladder volume and improve patient setup accuracy was needed. Purpose: The aim of this study is to investigate if the setup method by combining Optical Surface Management System (OSMS) and BladderScan can improve the accuracy of setup and accurately reproduce the bladder volume during radiotherapy of postoperative prostate cancer and to guide CTV-PTV margins for clinic. Method: The experimental group consisted of 15 postoperative prostate cancer patients who utilized a setup method that combined OSMS and BladderScan. This group recorded 103 setup errors, verified by CBCT. The control group comprised 25 patients, among whom 114 setup errors were recorded using the conventional setup method involving skin markers; additionally, patients in this group also exhibited spontaneous urinary suppression. The errors including lateral (Lat), longitudinal (Lng), vertical directions (Vrt), Pitch, Yaw, and Roll were analyzed between the two methods. The Dice similarity coefficient (DSC) and volume differences of the bladder between CBCT and planning CT were compared as the bladder concordance indicators. Results: The errors in the experimental group at Vrt, Lat, and Lng were 0.17 ± 0.12, 0.22 ± 0.17, and 0.18 ± 0.12 cm, and the control group were 0.25 ± 0.15, 0.31 ± 0.21, 0.34 ± 0.22 cm. The rotation errors of Pitch, Roll, and Yaw in the experimental group were 0.18 ± 0.12°, 0.11 ± 0.1°, and 0.18 ± 0.13°, and in the control group, they were 0.96 ± 0.89°, 1.01 ± 0.86°, and 1.02 ± 0.84°. The DSC and volume differences were 92.52 ± 1.65% and 39.99 ± 28.75 cm3 in the patients with BladderScan, and in the control group, they were 62.98 ± 22.33%, 273.89 ± 190.62 cm3. The P < 0.01 of the above performance indicators indicates that the difference is statistically significant. Conclusion: The accuracy of the setup method by combining OSMS and BladderScan was validated by CBCT in our study. The method in our study can improve the setup accuracy during radiotherapy of postoperative prostate cancer compared to the conventional setup method.

Best practices in robotic magnetic navigation-guided catheter ablation of cardiac arrhythmias, a position paper of the Society for Cardiac Robotic Navigation.

Robotic magnetic navigation (RMN)-guided catheter ablation (CA) technology has been used for the treatment of cardiac arrhythmias for almost 20 years. Various studies reported that RMN allows for high catheter stability, improved lesion formation and a superior safety profile. So far, no guidelines or recommendations on RMN-guided CA have been published. The aim of this consensus paper was to summarize knowledge and provide recommendations on management of arrhythmias using RMN-guided CA as treatment of atrial fibrillation (AF) and ventricular arrhythmias (VA). An expert writing group, performed a detailed review of available literature, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Recommendations on RMN-guided CA are presented in a guideline format with three levels of recommendations to serve as a reference for best practices in RMN procedures. Each recommendation is accompanied by supportive text and references. The various sections cover the practical spectrum from system and patient set-up, EP laboratory staffing, combination of RMN with fluoroscopy and mapping systems, use of automation features and ablation settings and targets, for different cardiac arrhythmias. This manuscript, presenting the combined experience of expert robotic users and knowledge from the available literature, offers a unique resource for providers interested in the use of RMN in the treatment of cardiac arrhythmias.

Feasibility of a Novel Surface-Guided Setup Technique to Reproduce Neck Curvature Using two Regions of Interest.

To improve the setup reproducibility of neck curvature using real-time optical surface imaging (OSI) guidance on 2 regions of interest (ROIs) to infer cervical spine (c-spine) curvature for surface-guided radiotherapy (SGRT) of head-and-neck (HN) and c-spine cancer. A novel SGRT setup approach was designed to reproduce neck curvature with 2 ROIs: upper-chest ROI and open-face ROI. It was hypothesized that the neck curvature could be reproduced if both ROIs were aligned within ±3 mm/2˚ tolerance. This was tested prospectively in 7 volunteers using real-time 3D-OSI guidance and lateral 2D-photography verification after the 3D and 2D references were captured from the initial conventional setup. Real-time SGRT was performed to align chest-ROI and face-ROI, and the longitudinal distance between them was adjustable using a head-support slider. Verification of neck curvature anteriorly and posteriorly was achieved by overlaying edge-extracted lateral pictures. Retrospectively, the relationship between anterior surface and spinal canal alignment was checked in 11 patients using their simulation CT (simCT) and setup cone-beam CT (CBCT). After the anterior surface was rigidly aligned, the spinal canal alignment was checked and quantified using the mean-distance-to-agreement (MDA) and DICE similarity index, and surface-to-spine correlation was calculated. The reproducibility of neck curvatures using the 2xROI SGRT setup is verified and the mean neck-outline-matching difference is within ±2 mm in lateral photographic overlays. The chest-ROI alignment takes 110 ± 58 s and the face-ROI takes 60 ± 35 s. When the anterior body surface is aligned (MDA = 1.1 ± 0.6 mm, DICE = 0.96 ± 0.02,) the internal spinal canal is also aligned (MDA = 1.0 ± 0.3 mm, DICE = 0.84 ± 0.04) in 11 patients. The surface-to-spine correlation is c = 0.90 (MDA) and c = 0.85 (DICE). This study demonstrates the feasibility of the novel 2-ROI SGRT setup technique to achieve reproducible neck and c-spine curvature regardless of neck visibility and availability as ROI. Staff training is needed to adopt this unconventional SGRT technique to improve patient setup.

A look-up-table development to facilitate CT simulation of MR-Linac treatment

While current MR-Linac (MRL) treatment workflows utilize a large table overlay during CT simulation to convert indexing between the two machines, we developed a look-up-table (LUT) as an alternative approach. After populating the LUT, index conversion factors were verified at three separate table locations. The resultant root-mean-square isocenter shifts on the MRL were 0.04/0.08 cm, 0.08/0.07 cm, and 0.09/0.08 cm with/without using the table overlay during simulation in the lateral, longitudinal, and vertical directions, respectively, which is within registration tolerance. Clinical implementation of the LUT has resulted in a more efficient MRL treatment workflow while maintaining accurate patient setup.

A Couch Mounted Smartphone-based Motion Monitoring System for Radiation Therapy

PurposeSurface-guided radiation-therapy (SGRT) systems are being adopted into clinical practice for patient setup and motion monitoring. However, commercial systems remain cost prohibitive to resource-limited clinics around the world. Our aim is to develop and validate a smartphone-based application using LiDAR cameras (such as on recent Apple iOS devices) for facilitating SGRT in low-resource centers. The proposed SGRT application was tested at multiple institutions, and validated using phantoms and volunteers against various commercial systems to demonstrate feasibility. Methods and MaterialsAn iOS application was developed in Xcode and written in Swift using the Augmented-Reality (AR) Kit and implemented on an Apple iPhone 13 Pro with a built-in LiDAR camera. The application contains multiple features: 1) visualization of both the camera and depth video feeds (at a ∼60Hz sample-frequency), 2) region-of-interest (ROI) selection over the patient's anatomy where motion is measured, 3) chart displaying the average motion over time in the ROI, and 4) saving/exporting the motion traces and surface map over the ROI for further analysis. The iOS application was tested to evaluate depth measurement accuracy for: 1) different angled surfaces, 2) different field-of-views over different distances, and 3) similarity to a commercially available SGRT systems (Vision RT AlignRT® and Varian IDENTIFY™) with motion phantoms and healthy volunteers across three institutions. Measurements were analyzed using linear-regressions and Bland-Altman analysis. ResultsCompared to the clinical system measurements (reference), the iOS application showed excellent agreement for depth (r=1.000,p<0.0001; bias=-0.07±0.24cm) and angle (r=1.000,p<0.0001; bias=0.02±0.69°) measurements. For free-breathing traces, the iOS application was significantly correlated to phantom motion (institute 1: r=0.99,p<0.0001; bias=-0.003±0.03cm; institute 2: r=0.98,p<0.0001; bias=-0.001±0.10cm; institute 3: r=0.97,p<0.0001; bias=0.04±0.06cm) and healthy volunteer motion (institute 1: r=0.98,p<0.0001; bias=-0.008±0.06cm; institute 2: r=0.99,p<0.0001; bias=-0.007±0.12cm; institute 3: r=0.99,p<0.0001; bias=-0.001±0.04cm). ConclusionThe proposed approach using a smartphone-based application provides a low-cost platform that could improve access to surface-guided radiation therapy accounting for motion.

Synthetic CT generation from MRI using 3D transformer-based denoising diffusion model.

Magnetic resonance imaging (MRI)-based synthetic computed tomography (sCT) simplifies radiation therapy treatment planning by eliminating the need for CT simulation and error-prone image registration, ultimately reducing patient radiation dose and setup uncertainty. In this work, we propose a MRI-to-CT transformer-based improved denoising diffusion probabilistic model (MC-IDDPM) to translate MRI into high-quality sCT to facilitate radiation treatment planning. MC-IDDPM implements diffusion processes with a shifted-window transformer network to generate sCT from MRI. The proposed model consists of two processes: a forward process, which involves adding Gaussian noise to real CT scans to create noisy images, and a reverse process, in which a shifted-window transformer V-net (Swin-Vnet) denoises the noisy CT scans conditioned on the MRI from the same patient to produce noise-free CT scans. With an optimally trained Swin-Vnet, the reverse diffusion process was used to generate noise-free sCT scans matching MRI anatomy. We evaluated the proposed method by generating sCT from MRI on an institutional brain dataset and an institutional prostate dataset. Quantitative evaluations were conducted using several metrics, including Mean Absolute Error (MAE), Peak Signal-to-Noise Ratio (PSNR), Multi-scale Structure Similarity Index (SSIM), and Normalized Cross Correlation (NCC). Dosimetry analyses were also performed, including comparisons of mean dose and target dose coverages for 95% and 99%. MC-IDDPM generated brain sCTs with state-of-the-art quantitative results with MAE 48.825±21.491 HU, PSNR 26.491±2.814dB, SSIM 0.947±0.032, and NCC 0.976±0.019. For the prostate dataset: MAE 55.124±9.414 HU, PSNR 28.708±2.112dB, SSIM 0.878±0.040, and NCC 0.940±0.039. MC-IDDPM demonstrates a statistically significant improvement (with p<0.05) in most metrics when compared to competing networks, for both brain and prostate synthetic CT. Dosimetry analyses indicated that the target dose coverage differences by using CT and sCT were within±0.34%. We have developed and validated a novel approach for generating CT images from routine MRIs using a transformer-based improved DDPM. This model effectively captures the complex relationship between CT and MRI images, allowing for robust and high-quality synthetic CT images to be generated in a matter of minutes. This approach has the potential to greatly simplify the treatment planning process for radiation therapy by eliminating the need for additional CT scans, reducing the amount of time patients spend in treatment planning, and enhancing the accuracy of treatment delivery.

Comparison of patient setup accuracy for optical surface-guided andX-ray-guided imaging with respect to the impact on intracranial stereotactic radiotherapy.

The objective of this work is to estimate the patient positioning accuracy of asurface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS). Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as abasis for determination of positioning accuracy. Atotal of 35patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a"standard" and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile. The interfractional measurement displacement vector of the SGRT system, σSGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σSGRT increased by about 20%. The standard deviation of the axis-related σSGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σSGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σSGRT, MC simulations served as ameasure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5mm cannot be ruled out. In contrast, MC simulations resulted in apositioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly achange in the facial surface relative to adefined point in the brain. In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.

RADT-47. MARGIN REDUCTION WITH THE INTRODUCTION OF INTRA-FRACTIONAL MONITORING USING IDENTIFY SGRT FOR FRAMELESS STEREOTACTIC CRANIAL RADIOSURGERY (SRS)

Abstract The purpose of this study was to evaluate the potential for margin reduction in clinical treatment settings based on the accuracy of Varian Identify SGRT (Surface-Guided Radiation Therapy). The study considered various factors such as patient setup variations, intrafraction movement, and unique facial features. Identify version 2.3.1 was installed on a Truebeam v2.7 system and commissioned according to AAPM TG3021 test recommendations. Identify generated reports on patient offsets in all six degrees of freedom during motion monitoring. These offsets were retrospectively compared with radiographic images (CBCT and MV planar images) to determine the accuracy of patient positioning achieved using surface guidance. A retrospective analysis of 36 patients was performed for a total of 125 fractions. The characteristics of the patient cohort (age range from 39 – 92 years) consisted of a mixture of 8 benign, 28 malignant lesions, 11 single, 25 standard fully-fractionated treatments and anatomical sites such as parietal, frontal, ventricle, base of skull, pons and acoustic neuromas. RESULTS: show that for this clinical cohort, the variance between Identify and radiographic imaging ranges from -0.02 to 0.08 cm, -0.09 to 0.10 cm, -0.09 to 0.09 cm and -0.81 to 0.74 degrees for the vertical, longitudinal, lateral and rotation respectively. This average variance in the translational axes is 0.0cm ± 0.0014 cm, indicating no directional preference. The 3D vector of the displacement detected achievable by Identify is 1 mm within a 95% confidence interval (CI). Based on the findings, the researchers concluded that a minimum GTV-PTV (Gross Tumor Volume-Planning Target Volume) margin of 1 mm is appropriate for intrafraction monitoring with Identify SGRT on the TrueBeam system for stereotactic cranial treatments. This information can increase the radiation oncologist's confidence in patient positioning during treatment delivery and potentially lead to a decrease in the GTV-PTV margin.

Radiation Therapy Skin Marking with Lancets Versus Electric Marking Pen (COMFORTATTOO)—6 Months Results on Cosmesis, Fading, and Patients’ Satisfaction From a Randomized, Double-Blind Trial

Introduction: Most of radiation oncology centers rely on set-up skin markings for patient setup during treatment delivery. Permanent dark-ink tattooing is the most popular marking method. COMFORTATTOO is a unicentric, randomized trial testing two permanent methods: lancets against an electric marking pen (Comfort Marker 2.0, CM). One substudy was undertaken to test if using the CM translates into a cosmesis, fading, or satisfaction benefit compared to the lancets. Methods: Patients aged 18 years or older referred to our department to receive RT were recruited. They were randomly assigned, in a 1:1 ratio, to receive set-up markings using lancets or CM. This substudy aimed to recruit all the living participants included in the main study. The primary endpoints were tattoos cosmesis, tattoos fading, and patients’ satisfaction six months after finishing the RT. Cosmetic and fading assessments were scored on a five-point ascending scale and patients’ satisfaction on a 10-point ascending scale. The trial is registered at ClinicalTrials.gov (number NCTXXXXXXXX). Results: Between April and September 2022, 92 patients were enrolled (45 assigned to lancets and 47 to CM) and assessed for the outcomes. Patients receiving CM had significantly better cosmetic markings, with a median score of 4.4 (vs. 3.7 for lancets, p <0.001). On the fading assessment, the CM was associated with lower scores compared to the lancets (median score of 1.3 and 3.3, respectively; p <0.001). No differences in patients’ satisfaction were observed with either method (median score of 10 for both arms, p=0.952). Conclusion: Our substudy results demonstrated that, six months after the end of RT, the CM produces better cosmetic markings with less fading compared to the lancets. These differences didn't translate into patients’ satisfaction superiority towards any method.

FLASH radiotherapy and the associated dosimetric challenges

At Lund University and Skåne University Hospital in Lund, Sweden, we have, as the first clinic, modified a clinical Elekta Precise linear accelerator for convertible delivery of ultra-high dose rate (FLASH) irradiation. Whereas recently published reviews highlighted the need for standardised protocols for ultra-high dose rate beam dosimetry to be able to determine the true potential of FLASH irradiation, several dosimetry studies as well as in-vitro and in-vivo experiments have been carried out at our unit. Dosimetric procedures for verification of accurate dose delivery of FLASH irradiation to cell cultures, zebrafish embryos and small animals have been established using radiochromic films and thermo-luminescent dosimeters. Also, recently the first experience of electron FLASH radiotherapy (FLASH-RT) in canine patients in our clinical setting was published. Our research facilities also include a laboratory for 3D polymer gel manufacturing. Recently, we started investigating the feasibility of a NIPAM polymer gel dosimeter for ultra-high dose rate dosimetry. Furthermore, in the bunker of the modified Elekta linear accelerator, a Surface Guided Radiotherapy (SGRT) system is accessible. The Catalyst™ system (C-Rad Positioning, Uppsala, Sweden) provides optical surface imaging for patient setup, real-time motion monitoring and breathing adapted treatment. Aiming at treating patients using ultra-high dose rates, a real-time validation of the alignment between the beam and the target is crucial as the dose is delivered in a fraction of a second. Our research group has during the last decade investigated and developed SGRT workflows which improved patient setup and breathing adapted treatment for several cancer patient groups. Recently, we also started investigating the feasibility of a real-time motion monitoring system for surface guided FLASH-RT. Both FLASH related studies; 3D polymer gel dosimetry and surface guided FLASH-RT are to our knowledge the first of their kind. Following an introduction to the field of FLASH and the associated dosimetric challenges, we here aim to present the two ongoing studies including some preliminary results.

A retrospective comparison of setup accuracy from CBCT and SGRT data in breast cancer patients

IntroductionBoth cone-beam computed tomography (CBCT) and surface-guided radiotherapy (SGRT) are used for breast patient positioning verification before treatment delivery. SGRT may reduce treatment time and imaging dose by potentially reduce the number of CBCT needed. The aim of this study was to compare the displacements resulting in positioning from the Image Guided Radiation Therapy (IGRT) 3D and SGRT methods and to design a clinical workflow for SGRT implementation in breast radiotherapy to establish an imaging strategy based on the data obtained. MethodsFor this study 128 breast cancer patients treated with 42.5 Gy in 16 fractions using 3D conformal radiotherapy with free breathing technique were enroled. A total of 366 CBCT images were evaluated for patient setup verification and compared with SGRT. Image registrations between planning CT images and CBCT images were performed in mutual agreement and in online mode by three health professionals. Student's paired t‐test was used to compare the absolute difference in vector shift, measured in mm, for each orthogonal axis (x, y, z) between SGRT and CBCT methods. The multidisciplinary team evaluated a review of the original clinical workflow for SGRT implementation and data about patients treated with the updated workflow were reported. ResultsComparison of the shifts obtained with IGRT and SGRT for each orthogonal axis (for the x-axes the average displacement was 0.9 ± 0.7 mm, y = 1.1 ± 0.8 mm and z = 1.0 ± 0.7 mm) revealed no significant statistical differences (p > 0.05). Using the updated workflow the difference between SGRT and IGRT displacements was <3 mm in 91.4 % of patients with a reduction in total treatment time of approximately 20 %, due to the reduce frequency of the CBCT images acquisition and matching. ConclusionsThis study has shown that IGRT and SGRT agree in positioning patients with breast cancer within a millimetre tolerance. SGRT can be used for patient positioning, with the advantages of reducing radiation exposure and shorter overall treatment time.

Kinetic Energy of Secondary Particles Produced from Various Electromagnetic Interactions in Water: A Monte Carlo Study

Advancements in imaging systems including Electronic Portal Imaging Devices (EPIDs) play a great role in radiotherapy treatment. It was developed as a verification tool for patient setup during radiotherapy sessions and also become a promising tool for the determination of the accurate placement of radiation beams. However, as part of quality assurance, individual patient treatments are often verified by patient-specific quality control measurements such as before treatment (pretreatment) or during treatment (in vivo). It has been shown that in vivo dosimetry using an electronic portal imaging device (EPID) is an effective QC tool to detect errors and this method has been clinically applied to various treatments. The introduction of advanced EPID technology has led to an interest in its application for dose conformation and dose deposition. Moreover, dose deposition is subject to uncertainties due to several factors, including the presence of secondary particles. Thus, knowing the physical processes that produced the secondary particles as well as their average kinetic energy will help to provide valuable information about the effective filtering of these particles or the possible use of these particles for other applications. In this study, Monte Carlo simulations are performed to determine the average kinetic energy of detected secondary particles, specifically photons, electrons, and positrons produced by each particular physical interaction as a function of detector position using GATE v9.0. The virtual radiotherapy set-up is composed of the box water phantom, which is the target in the simulations with a dimension of 20 cm × 20 cm × 20 cm, an EPID system (detector), and a beam source in which it uses three (3) beams situated at varying positions with an energy of 6 MeV. The monoenergetic pencil beam source is placed 90 cm away from the center of the target and is directed toward the target (+x-axis) while the EPID (detector) is set as 120 cm SDD (source-to-detector distance). Moreover, the photon beam with 10 million primaries is set with varying field sizes of 1 cm × 1 cm, 3 cm × 3 cm, 6 cm × 6 cm, and 9 cm × 9 cm. Overall, the results show that the highest average kinetic energy among secondary particles produced by each physical interaction are electrons coming from Compton scattering (∼ 3 MeV), followed by positrons and electrons from pair production (∼ 2.4 MeV), photons from annihilation and bremsstrahlung (∼ 0.5 MeV), and electrons from ionization (∼ 0.13 MeV).

Two novel stereotactic radiotherapy methods for locally advanced, previously irradiated head and neck cancers patients

To determine the feasibility and utility of conebeam CT-guided stereotactic radiotherapy for locally recurrent, previously irradiated head and neck cancer (HNC) patients on the Halcyon, a ring delivery system (RDS). This research aims to quantify plan quality, treatment delivery accuracy, and overall efficacy by comparing against novel clinical TrueBeam HyperArc method. Ten recurrent HNC patients who were treated at our institution on TrueBeam (6MV-FFF) for 30 to 40 Gy in 3 to 5 fractions with noncoplanar HyperArc plans were re-planned on Halcyon (6MV-FFF). These plans were re-planned with the same Acuros-based dose engine. Additionally, we used site-specific full/partial coplanar VMAT arcs. PTV coverage, mean dose to GTV, maximum dose to organs-at-risk (OAR), beam-on time (BOT), and quality assurance (QA) results were investigated and compared. Halcyon provided highly conformal HNC SRT plans with slightly superior mean PTVD99 coverage (96.7% vs 95.5%, p = 0.071), and slightly lower mean GTV dose (37.8 Gy vs 38.2 Gy, p = 0.241) when compared to the HyperArc plans. Differences in plan conformality and maximum dose to OARs were statistically insignificant. Due to Halcyon's coplanar geometry, D2cm was significantly higher (p = 0.001) but Halcyon did result in a reduced normal brain dose by 1 Gy on average and up to 5.2 Gy in some cases. Halcyon provided similar patient-specific QA pass rates with a 2%/2mm gamma criteria (98.2% vs 98.5%) and independent in-house Monte Carlo second check results (97.7% vs 98.2%), suggesting identical treatment delivery accuracy. Halcyon plans resulted in slightly longer beam-on time (3.16 vs 2.30 minutes, p = 0.010), however door-to-door patient time is expected to be <10 minutes. Compared to clinical TrueBeam HyperArc, Halcyon SRT plans provided similar plan quality and treatment delivery accuracy with a potentially faster overall treatment using fully automated patient setup and verification. Rapid delivery of recurrent HNC SRT may reduce intrafraction motion errors while also improving patient compliance and comfort. To provide high-quality of HNC SRT similar to HyperArc, we recommend Halcyon users consider commissioning this novel method. This method will be useful for remote and underserved patient cohorts including Halcyon-only clinics as well.

Teamwork and mental workload in postsurgical pediatric patient handovers: Prospective effect evaluation of an improvement intervention for OR-PICU patient transitions

Postsurgical handover of pediatric patients from operating rooms (OR) to pediatric intensive care units (PICU) is a critical step. This transition is susceptible to errors and inefficiencies particularly if poor multidisciplinary teamwork occurs. Despite wide adoption of standardized handover interventions, comprehensive investigations into joint effects for patient care and provider outcomes are scarce. We aimed to improve OR-PICU handovers quality and sought to evaluate the intervention with particular attention to patient care effects and provider outcomes. A prospective, before-after-study design with an interrupted-series and a multi-source, mixed-methods evaluation approach was established. Drawing upon a participative plan-do-study-act approach, a standardized, checklist-based handover process was designed and implemented. For effect assessments, we observed OR-PICU handovers on site (pre implementation: n = 31, post: n = 30), respectively, with standardized expert observation and provider self-report tools (n = 111, n = 110). Setting was a tertiary Pediatric University Hospital. Supplementary qualitative, semi-structured interviews were conducted, and a general inductive content analysis approach was used to identify key facilitators and barriers on implementation. Improvement efforts focused on stepwise implementation of (1) standardized handover process and (2) a checklist for multi-professional OR-PICU handover communication. We observed significant increases in team and patient setup (pre: 79.3%, post: 98.6%, p < .01), enhanced team engagement (pre: 50%, post: 81.7%, p < .01), and comprehensive information transfer by the anesthesia sub-team (pre: 78.6%, post: 87.3%, p < .01). Expert-rated teamwork outcomes were consistently higher, yet self-reported teamwork did not change over time. Provider perceived stress and disruptions did not change, mental workload tended to decrease over time (pre: M = 3.2, post: 2.9, p = .08). Comprehensiveness of post-operative patient information reported by PICU physician increased significantly: pre: 65.9%, post: 76.2%, p < .05. After implementation, providers acknowledged the importance of standardized handover practices and associated benefits for facilitation of information transfer and comprehensiveness. Among reported barriers were obstacles during implementation as well as insufficient consideration of professionals’ individual workflow after surgery.Conclusion: A multidisciplinary intervention for postsurgical pediatric patient handovers was associated with improved expert-rated teamwork and fewer omissions of key patient information over time. Inconsistent results were obtained for provider-rated mental workload and teamwork outcomes. The findings contribute to a better understanding concerning the interplay of teamwork and provider cognitions in the course of establishing safe patient transitions in pediatric care.What is Known:• Transfer of critically ill children conveys significant challenges for interprofessional communication and teamwork. Prospective research into interventions for safe and efficient handover practices of OR PICU patient transitions is necessary.• Checklists are assumed to facilitate cognitive load among providers in acute clinical environments.What is New:• A standardized, checklist-based handover intervention was associated with improvements in team set-up and information transfer. Provider outcomes such as mental workload and stress did not change over time.• The combination of teamwork and provider assessments allows a more nuanced understanding of implementation barriers and sustainable effects in course of OR-PICU handover interventions.

Setup accuracy and margins for surface-guided radiotherapy (SGRT) of head, thorax, abdomen, and pelvic target volumes

The goal of the study was to evaluate the inter- and intrafractional patient setup accuracy of target volumes located in the head, thoracic, abdominal, and pelvic regions when using SGRT, by comparing it with that of laser alignment using patient skin marks, and to calculate the corresponding setup margins. A total of 2303 radiotherapy fractions of 183 patients were analyzed. All patients received daily kilovoltage cone-beam computed tomography scans (kV-CBCT) for online verification. From November 2019 until September 2020, patient setup was performed using laser alignment with patient skin marks, and since October 2020, using SGRT. The setup accuracy was measured by the six degrees of freedom (6DOF) corrections based on the kV-CBCT. The corresponding setup margins were calculated using the van Herk formula. Analysis of variance (ANOVA) was used to evaluate the impact of multiple factors on the setup accuracy. The inter-fractional patient setup accuracy was significantly better using SGRT compared to laser alignment with skin marks. The mean three-dimensional vector of the translational setup deviation of tumors located in the thorax, abdomen, and pelvis using SGRT was 3.6 mm (95% confidence interval (CI) 3.3 mm to 3.9 mm) and 4.5 mm using laser alignment with skin marks (95% CI 3.9 mm to 5.2 mm; p = 0.001). Calculation of setup margins for the combined inter- and intra-fractional setup error revealed similar setup margins using SGRT and kV-CBCT once a week compared to laser alignment with skin marks and kV-CBCT every other day. Furthermore, comparable setup margins were found for open-face thermoplastic masks with AlignRT compared to closed-face thermoplastic masks with laser alignment and mask marks. SGRT opens the possibility to reduce the number of CBCTs while maintaining sufficient setup accuracy. The advantage is a reduction of imaging dose and overall treatment time. Open-face thermoplastic masks may be used instead of closed-face thermoplastic masks to increase the patient's comfort.

Characteristics of detection accuracy of the patient setup using InBore optical patient positioning system.

This study aimed to evaluate the detection accuracy of the AlignRT-InBore system in surface-guided radiation therapy using a phantom and to determine the feasibility of the system by conducting a comparative analysis with cone-beam computed tomography (CBCT) registration. The AlignRT-InBore system integrated with the ETHOS Therapy was used. A phantom and a QUASAR phantom were employed to examine the specific areas of interest relevant to clinical cases. The evaluation involved monitoring translations for approximately 30 min and assessing the position detection accuracy for static and moving objects. Fifty clinical cases were used to evaluate the position detection accuracy and its relationship with the localization accuracy of CBCT before treatment. The detection accuracy of static and moving objects was within 1.0 mm using the phantom. However, the longitudinal direction tended to be larger than the other directions. Regarding the accuracy of localization in clinical cases, a strong and statistically significant (p<0.01) correlation was observed in each direction. A detection accuracy within 1.0 mm is possible for static and moving objects. The detection accuracy of the patient setup using the InBore optical patient positioning system was extremely high, and the patient could be detected with high precision, suggesting its usefulness.

Comparison and evaluation of different deep learning models of synthetic CT generation from CBCT for nasopharynx cancer adaptive proton therapy.

Cone-beam computed tomography (CBCT) scanning is used for patient setup in image-guided radiotherapy. However, its inaccurate CT numbers limit its applicability in dose calculation and treatment planning. This study compares four deep learning methods for generating synthetic CT (sCT) to determine which method is more appropriate and offers potential for further clinical exploration in adaptive proton therapy for nasopharynx cancer. CBCTs and deformed planning CT (dCT) from 75 patients (60/5/10 for training, validation and testing) were used to compare cycle-consistent Generative Adversarial Network(cycleGAN), Unet, Unet+cycleGAN and conditionalGenerative Adversarial Network (cGAN) for sCT generation. The sCT images generated by each method were evaluated against dCT images using mean absolute error (MAE), structural similarity (SSIM), peak signal-to-noise ratio (PSNR), spatial non-uniformity (SNU) and radial averaging in the frequency domain. In addition, dosimetric accuracy was assessed through gamma analysis, differences in water equivalent thickness (WET), and dose-volume histogram metrics. The cGAN model has demonstrated optimal performance in the four models across various indicators. In terms of image quality under global condition, the average MAE has been reduced to 16.39HU, SSIM has increased to 95.24%, and PSNR has increased to 28.98. Regarding dosimetric accuracy, the gamma passing rate (2%/2mm) has reached 99.02%, and the WET difference is only 1.28mm. The D95 value of CTVs coverage and Dmax value of spinal cord, brainstem show no significant differences between dCT and sCT generated by cGAN model. The cGAN model has been shown to be a more suitable approach for generating sCT using CBCT, considering its characteristics and concepts. The resulting sCT has the potential for application in adaptive proton therapy.