Journal of Applied Clinical Medical Physics最新文献

Purpose: Methods have been developed that apply image processing to 4DCTs to generate 4DCT-ventilation/perfusion lung imaging. Traditional methods for 4DCT-ventilation rely on Hounsfield-Unit (HU) density-change methods and suffer from poor numerical robustness while not providing 4DCT-perfusion data. The purpose of this work was to evaluate the clinical differences between classic HU-based 4DCT-ventilation approaches and novel 4DCT-ventilation/perfusion approaches.

Methods: Data from 63 lung cancer patients enrolled in a functional avoidance clinical trial were analyzed. 4DCT-data were used to generate four lung-function images: (1) classical HU-based 4DCT-ventilation ("4DCT-vent-HU"), and three novel, statistically robust methods: (2) 4DCT-ventilation based on the Mass Conserving Volume Change ("4DCT-vent-MCVC"), (3) 4DCT-ventilation using the Integrated Jacobian Formulation, and (4) 4DCT-perfusion. A radiologist reviewed all images for ventilation/perfusion defects (scored as yes/no) and the scores for the novel approaches were compared to those of 4DCT-vent-HU using receiver operating characteristic (ROC) analysis. Functional contours were generated using thresholding methods, and the contours from the three novel 4DCT-ventilation methods were compared against that from 4DCT-vent-HU (Dice similarity coefficients [DSC]). Functional mean lung dose (fMLD) and dose-function metrics were compared against dose-function metrics using 4DCT-vent-HU.

Results: ROC analysis revealed accuracy in the range of 0.55 to 0.73 comparing radiologist interpretations of 4DCT-vent-HU against the three novel approaches. Average DSC values were 0.41 ± 0.19, 0.44 ± 0.16, and 0.42 ± 0.17 comparing 4DCT-vent-HU to 4DCT-vent-IJF, 4DCT-vent-MCVC, and 4DCT-perf, respectively. All novel imaging methods showed significant differences (p < 0.01) in dose-function metrics compared to those of 4DCT-vent-HU. 4DCT-vent-MCVC and 4DCT-Perf depicted the smallest and largest differences from 4DCT-vent-HU in fMLD (3.51 ± 3.20 Gy and 5.90 ± 5.29 Gy, respectively).

Conclusion: This is the first work to comprehensively compare novel 4DCT-ventilation/perfusion methods against classical formulations. Our data show that significant differences between the 4DCT-based functional imaging methods exist, suggesting that studies are needed to evaluate which methods provide the most robust clinical results.

Background: As medical linear accelerator technology advances, enabling higher dose rate deliveries, hypofractionation regimens has increased. This necessitates respiratory gating systems that synchronize radiation delivery with tumor position, requiring simple rigorous quality assurance (QA) to ensure treatment accuracy and patient safety.

Purpose: This study aimed to propose log-based QA for respiratory-gated radiation therapy using the respiratory gating system and treatment machine.

Methods: 4D CT scans were performed with a Varian motion phantom using a Varian Respiratory Gating for Scanner (RGSC). A treatment plan using 25%-75% respiratory phases with 100 MU was created and delivered to a solid water phantom. Treatment logs containing respiratory signals, beam on/off flags, and frame information were extracted from the treatment planning system's offline review. Log file analyses were conducted using in-house softwares to assess temporal synchronization between respiratory phases and beam triggers. Output measurements using a calibrated ion chamber (FC65G) were performed to evaluate dosimetric accuracy. Additionally, EPID images were acquired in cine mode and analyzed frame-by-frame to independently verify beam delivery timing.

Results: Log file analysis revealed precise temporal synchronization, with mean time differences of 0.03 s ± 0.05 s between the planned 25% phase and beam-on, and -0.04 s ± 0.05 s between 75% phase and beam-off. The log-derived beam-on duration (2.61 s ± 0.02 s) closely matched the planned duration (2.66 s ± 0.00 s). Three-month log data showed consistent temporal accuracy, with trigger-on times remaining stable at 2.60 s ± 0.01 s across all measurements. Supporting ion chamber measurements confirmed dosimetric agreement between gating and non-gating modes (difference: 0.05 cGy ± 0.09 cGy) CONCLUSIONS: The proposed log file-based QA method demonstrated high accuracy and reproducibility in assessing respiratory gating performance. This approach provides an efficient, objective method for standardizing QA procedures in respiratory-gated radiation therapy, enhancing treatment accuracy and patient safety.

Purpose: In linear accelerators, deviations in the x-ray focal spot position significantly affect the accuracy of radiation therapy. However, as the focal spot position in bore-type linac systems such as the Radixact system, cannot be assessed using conventional methods, a new evaluation method is required. This study aimed to develop a novel method to measure the focal spot position of Radixact and evaluate any deviations from the ideal x-ray focal spot position.

Methods: A structurally simplified measurement system was developed to evaluate the focal spot position of the Radixact system. This system consisted of a vertically aligned metal bar and an ionization chamber, which was moved stepwise to acquire the beam profiles. The focal spot position deviation was calculated based on the center differences of the profiles obtained from two different upstream and downstream locations of the metal bar.

Results: The measurement results indicated that the focal spot position shift was 0.42 mm and -0.36 mm at the target height in the IEC-X and -Y directions, respectively. The measurement uncertainty was 0.187 mm, confirming a slight deviation from the ideal focal position.

Conclusions: This study developed a novel method to accurately evaluate the x-ray focal spot position of the Radixact system, which can potentially be applied to other conventional linear accelerators and bore-type systems, such as Halcyon, to improve the accuracy of radiotherapy. However, its generalizability and applicability to different radiotherapy machines must be explored further.

Background: The use of deep learning-based auto-contouring algorithms in various treatment planning services is increasingly common. There is a notable deficit of commercially or publicly available models trained on large or diverse datasets containing high-dose-rate (HDR) brachytherapy treatment scans, leading to poor performance on images that include HDR implants.

Purpose: To implement and evaluate automatic organs-at-risk (OARs) segmentation models for use in prostatic-and-gynecological computed tomography (CT)-guided high-dose-rate brachytherapy treatment planning.

Methods and materials: 1316 computed tomography (CT) scans and corresponding segmentation files from 1105 prostatic-or-gynecological HDR patients treated at our institution from 2017 to 2024 were used for model training. Data sources comprised six CT scanners including a mobile CT unit with previously reported susceptibility to image streaking artifacts. Two UNet-derived model architectures, UNet++ and nnU-Net, were investigated for bladder and rectum model training. The models were tested on 100 CT scans and clinically-used segmentation files from 62 prostatic-or-gynecological HDR brachytherapy patients, disjoint from the training set, collected in 2024. Performance was evaluated using the Dice-Similarity-Coefficient (DSC) between model predicted contours and clinically-used contours on slices in common with the Clinical-Target-Volume (CTV). Additionally, a blinded evaluation of ten random test cases was conducted by three experienced planners.

Results: Median (interquartile range) 3D DSC on CTV-containing slices were 0.95 (0.04) and 0.87 (0.09) for the UNet++ bladder and rectum models, respectively, and 0.96 (0.03) and 0.88 (0.10) for the nnU-Net. The rank-sum test did not reveal statistically significant differences in these DSC (p = 0.15 and 0.27, respectively). The blinded evaluation scored trained models higher than clinically-used contours.

Conclusion: Both UNet-derived architectures perform similarly on the bladder and rectum and are adequately accurate to reduce contouring time in a review-and-edit context during HDR brachytherapy planning. The UNet++ models were chosen for implementation at our institution due to lower computing hardware requirements and are in routine clinical use.

Purpose: Breast cancer is a neoplastic disease with high prevalence among women. Radiotherapy is one of the principal treatment modalities for this disease, but it poses significant challenges. This study aimed to compare and evaluate the technical and dosimetric performance of conventional C-arm linac systems and a new design, Halcyon, in the context of breast radiotherapy.

Methods: The study included ten patients who had undergone left breast radiotherapy. Additionally, breast radiotherapy was simulated with an anthropomorphic phantom, and similar planning studies were performed. A total of 40 treatment plans were prepared for ten patients using the field-in-field (FinF) and volumetric modulated arc therapy (VMAT) techniques on both TrueBeam and Halcyon systems. Subsequently, treatment plans were created for anthropomorphic phantoms using both techniques on both devices. The dosimetric comparisons were conducted on treatment plans with different treatment techniques on both devices. An anthropomorphic phantom was employed to ascertain the surface dose during treatment, with irradiation conducted in the following with the OSL dosimetry method.

Results: Patient plan comparisons showed no statistically significant differences in planning target volume (PTV) outcomes between techniques and devices. Upon analysis of the organ at risk (OAR), statistically significant differences were identified for FinF in both devices for low-dose regions. Analysis of the OSL results obtained from phantom irradiations revealed that the Halcyon results were higher than those obtained with the TrueBeam for both techniques. Additionally, a comparison of OSL results with the TPS data revealed discrepancies of up to 18% within the field and up to 22% outside the field. Furthermore, Halcyon demonstrated higher Monitor Unit (MU) values for both techniques, while still maintaining shorter treatment times.

Conclusion: The Halcyon demonstrated comparable technical and dosimetric outcomes to conventional C-arm linac in breast radiotherapy. Its distinctive design features contribute to the implementation of efficient and secure treatment modalities.

Introduction: Medical physics is a fulfilling profession where physics is applied to advance human health. However, many are uninformed of the role of physicists in medicine, and students are unaware of this career pathway. This study presents a pilot 1-year program for science teachers to learn about physics in medicine and share with students and teachers.

Methods: A cohort of middle school and high school science teachers were selected to learn about physics in medicine, develop lesson plans for their students, participate in a Physics in Medicine field trip hosted at a cancer hospital, and concluded with a professional development day for other regional science teachers. Surveys were conducted throughout the program to assess attitudes toward teaching medical physics, content knowledge of medical physics, collaboration, and demographic information from participants.

Results: The program was implemented over the course of a year which included 5 school districts, 10 science teachers, and hundreds of students. After participating in the program, teacher scores on surveys regarding attitudes toward teaching medical physics and content knowledge significantly increased for the cohort. Strong collaboration between teaching pairs was maintained throughout the program based on survey responses. Teachers participating in the 1-day professional development program also benefited from the program based on survey responses regarding attitudes toward medical physics and interest in learning more about medical physics.

Discussion: This pilot study demonstrated the feasibility and effectiveness of an educational model for teachers' understanding and connecting medical physics with students in their schools.  The program was well received by teachers and students, and this manuscript provides guidelines for effective replication of the curriculum at other institutions.

Purpose: Volumetric-modulated arc therapy (VMAT) treatment planning allows a compromise between a sufficient coverage of the planning target volume (PTV) and a simultaneous sparing of organs-at-risk (OARs). Particularly in the case of lung tumors, deciding whether it is possible or worth spending more time on further improvements of a treatment plan is difficult. Therefore, this work aims to develop a knowledge-based, structure-dependent, automated dose volume histogram (DVH) prediction module for lung tumors.

Methods: The module is based on comparing geometric relationships between the PTV and the surrounding OARs. Therefore, treatment plan and structure data of 106 lung cancer cases, each treated in 28 fractions and 180 cGy/fx, were collected. To access the spatial information, a two-dimensional metric named overlap volume histogram (OVH) was used. Due to the rotational symmetry of the OVH and the typically coplanar setup of the VMAT technique, OVH is complemented by the so-called overlap-z-histogram (OZH). A set of achievable DVHs is predicted by identifying plans in the database with similar OVH and OZH. By splitting the dataset into a test set of 22 patients and a training set of 84 patients, the prediction capability of the OVH-OZH combination was evaluated. For comparison between the predicted and achieved DVH curves the coefficient of determination R² was calculated.

Results: The total lung showed strong linearity between predicted and achieved DVH curves for the OVH-OZH combination, resulting in a $R^2$ value close to 1 (0.975 ± 0.022). The heart benefits the most of the OZH resulting in a high prediction capability, with a higher $R^2$ of 0.962 ± 0.036 compared to the prediction with OVH only (0.897 ± 0.087).

Conclusion: The combination of OZH and OVH was suitable for building a knowledge-based automated DVH prediction module. Implementing this method into the clinical workflow of treatment planning will contribute to advancing the quality of VMAT plans.

Purpose: This work introduces BreastWatch, a Varian Eclipse script tool designed to help medical physicists, dosimetrists, and radiation oncologists easily inspect and improve External Beam Breast Treatment (EBBT) plans using automatic evaluation of protocol dose-constraints enhanced by a Community-Based approach.

Methods: BreastWatch examines Eclipse EBBT Plans and Plan Sums, automatically testing the plan's DVH against built-in international EBBT protocol (NRG RTOG1005, ICR Fast-Forward, ICR FAST, and EUROPA 1.2) dose-constraints. Results are displayed using traffic lights and an overall BW-SCORE. To overcome protocol dose-constraints limitations, the script can export plan data and dose values in CSV format to build a Community-Based Plan Library. These data are automatically read back in BreastWatch to check plans against the statistical distribution of similar Community plans and compute a CB-SCORE, which complements the protocol-based BW-SCORE. In this paper, BreastWatch v.1.6.5.0 script's design and strengths are examined and discussed, after extensive testing with more than 800 EBBT plans by six experienced planners. In a preliminary analysis, the usefulness of the CB approach is investigated by examining the chronological series of two dose-constraints values (Contra-Lung V3Gy and Heart Average Dose) before and after its introduction in BreastWatch.

Results: We found BreastWatch to speed up the EBBT planning process, while at the same time helping to improve the treatment plans in terms of PTVs coverage and uniformity, sparing of OARs, consistency, and robustness among different planners. The preliminary analysis of the chronological series of two dose-constraints values for a subgroup of 68 EBBT plans shows a trend (p-value = 0.07) for values to be improved and more consistent after the CB approach introduction.

Conclusions: The BreastWatch script is a useful tool for the automatic evaluation of Eclipse EBBT plans. BreastWatch and its Community-Based features have been found to be a simple but effective automation approach to improve the EBBT planning process.

Introduction: Many artificial intelligence (AI) solutions have been proposed to enhance the radiotherapy (RT) workflow, but limited applications have been implemented to date, suggesting an implementation gap. One contributing factor to this gap is a misalignment between AI systems and their users. To address the AI implementation gap, we propose a human-centric methodology, novel in RT, for an interface design of an AI-driven RT treatment error detection system.

Methods: A 5-day design sprint was set up with a multi-disciplinary team of clinical and research staff and a commercial company. In the design sprint, an interface was prototyped to aid medical physicists in catching treatment errors during daily treatment fractions using dose-guided RT (DGRT) with a portal imager.

Results: The design sprint resulted in a simulated prototype of an interface supported by all stakeholders. Important features of an interface include the AI certainty metric, explainable AI features, feedback options, and decision aid. The prototype was well-received by expert users.

Conclusion/discussion: Using a co-creation strategy, which is a novel approach in RT, we were able to prototype a novel human-interpretable interface to detect RT treatment errors and aid the DGRT workflow. Users showed confidence that the overall design method and the proposed prototype could lead to a viable clinical implementation.

Background: In vivo transit dosimetry using an electronic portal imaging device (EPID-IVTD) is an important tool for verifying the accuracy of radiation therapy treatments. Despite its potential, the implementation of EPID-IVTD in breast intensity modulated radiation therapy (IMRT) treatments has not yet been standardized, limiting its clinical adoption. A standardized EPID-IVTD method could enhance treatment accuracy and improve patient safety in routine clinical practice.

Purpose: This study aims to develop a method for EPID-IVTD for whole breast IMRT treatment.

Methods: Gamma passing rates (GPRs) analysis was the basis of the work conducted on a dataset of 50 patients. The first phase of the work focused on the identification of the reference fraction. In the second phase a method for performing EPID-IVTD was implemented. Lower-tolerance and -action limits (l-TL and l-AL), as introduced by AAPM TG 218, were employed to determine the reference fraction and used as alert and alarm thresholds, respectively, in EPID-IVTD monitoring.

Results: The first treatment fraction demonstrated the best dosimetric agreement with the theoretical plan and was therefore used as the reference in the second phase of the study. EPID-IVTD results showed that 75% of the GPRs ranged from 97.5% to 99.9%, 93.83% were above the l-TL, 4.31% fell between l-TL and l-AL, and 1.86% were below l-AL.

Conclusions: A method for the implementation of an effective EPID-IVTD in whole breast IMRT treatment was developed and is now routinely applied at our center, enabling efficient monitoring in clinical practice.