Physics in medicine and biology最新文献

{"title":"Cherenkov-excited fluorescence imaging for small-field dosimetry and SRS plan verification: a feasibility study.","authors":"Mehmet Fazil Enkavi, Hasan Uysal, Kaan Oysul, Sait Sirin, Hulya Yavuz Ersan","doi":"10.1088/1361-6560/aea5cf","DOIUrl":"10.1088/1361-6560/aea5cf","url":null,"abstract":"<p><p><i>Objective.</i>To develop a high-spatial-resolution Cherenkov-excited fluorescence dosimetry system (CEFD) with rapid optical readout using quinine sulfate solution and evaluate its feasibility for small-field dosimetry and verification of patient-derived stereotactic radiosurgery (SRS) dose distributions.<i>Approach.</i>A 3D-printed optical phantom containing 1 g l^-1quinine sulfate solution was imaged with a complementary metal-oxide-semiconductor camera through a 45° mirror. Sensitive-volume thicknesses of 2.5, 5, 10 and 15 mm were compared using calibration response, signal-to-noise ratio, output factors, dose-rate dependence, and small-field beam profiles benchmarked against a PTW 60023 microSilicon detector. The selected CEFD configuration was further evaluated for thermal response, repeatability, signal drift, low-MU response, and small-field gamma performance, and then used for fixed-gantry verification of 31 patient-derived SRS dose distributions. GafChromic EBT3 film was used as the high-spatial-resolution comparator.<i>Main results.</i>The CEFD achieved 0.065 mm pixel^-1spatial sampling. CEFD-10 showed the most balanced overall performance across sensitivity, dose-rate response, output-factor agreement, and small-field profile measurements. Dose-rate deviations remained within 1.7% at 300-1400 MU min^-1. Passive heat sinking reduced the coefficient of variation from 0.26%-0.13% and limited signal drift from 4.3%-0.97% over 30 consecutive measurements. For the 0.5 × 0.5 cm²field, the CEFD-10 central-axis dose ratio relative to the treatment planning system-projected dose remained within ±2% from 10 MU onward. For 0.5 × 0.5-3 × 3 cm²static fields, CEFD-10 achieved 99.56%-100.0% global 2%/1 mm gamma passing rates with a 10% low-dose threshold. For patient-derived SRS verification, CEFD-10 achieved mean global gamma passing rates of 99.47 ± 1.58% and 97.53 ± 3.58% for 2%/2 mm and 2%/1 mm criteria, respectively, with mean differences from EBT3 film of -0.32% and -0.21%, respectively.<i>Significance.</i>This study demonstrates compact, high-spatial-resolution, rapid-readout optical dosimetry for small-field and patient-derived SRS dose patterns. Agreement with EBT3 film supports CEFD-10 as a controlled-geometry SRS dose verification.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148930925","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Monte Carlo intercomparison of TG-43 dosimetric parameters for clinical192Ir and125I brachytherapy sources.","authors":"Lucas F Araújo, Asif Amin, Adriano P Sabino, Telma C F Fonseca","doi":"10.1088/1361-6560/aea7f6","DOIUrl":"10.1088/1361-6560/aea7f6","url":null,"abstract":"<p><p><i>Objective.</i>This study presents a rigorous, simultaneous Monte Carlo (MC) intercomparison of three general-purpose computational codes, MCNP6.2, TOPAS 3.9, and PHITS 3.341, for the calculation and validation of TG-43 dosimetric parameters for the clinical microSelectron-HDR v2Ir and Theragenics-AgX100I brachytherapy sources under realistic, unsimplified photon emission spectra.<i>Approach.</i>Simulations were performed in a spherical liquid water phantom with a radius of 18.5 cm to ensure full-scatter conditions. Dose was scored in small, distance-dependent spherical water scoring cells with varying radii. Discrete, unsimplified photon emission spectra from ICRP Publication 107 were implemented in all three codes. To address gaps in the literature, a computationally efficient simplified geometry previously adopted for theIr source was evaluated, while theI source was modeled with high geometric fidelity. The radial dose and anisotropy functions were calculated, the radial dose data were fitted using fifth-degree polynomials, and the resulting datasets were benchmarked against established TG-43 consensus reference data.<i>Main results.</i>The three MC codes demonstrated good overall agreement. For theIr source, the simplified geometry reproduced the consensus reference data within thecriterion over the clinically relevant radial range, demonstrating its dosimetric suitability within the TG-43 framework. For the low-energyI source, larger deviations, reaching approximately, were observed at short radial distances (cm), consistent with the greater sensitivity of low-energy photon transport to attenuation and shielding effects associated with the source encapsulation and internal components. At distances beyond approximatelycm, the results showed substantially improved agreement, with deviations generally remaining within. Fifth-degree polynomial fitting accurately reproduced the radial dose function, with deviations predominantly remaining below the recommendedcriterion within the clinically relevant radial intervals.<i>Significance.</i>This work establishes a robust, cross-validated computational baseline for brachytherapy dosimetry using general-purpose MC codes under realistic photon emission spectra. The validation of the simplifiedIr geometry supports its use in computationally efficient simulations, while the characterization of the low-energyI source provides relevant information for high-precision dosimetry and future investigations of low-energy radiation interactions in radiosensitization studies.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148977504","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of computational methods used to optimize transmission x-ray targets for 100- to 500-kv x-ray tubes.","authors":"Benjamin Insley, Mohammad Salehpour, Dirk Bartkoski","doi":"10.1088/1361-6560/aea469","DOIUrl":"10.1088/1361-6560/aea469","url":null,"abstract":"<p><p><i>Objective.</i>While the process of designing a low-to-medium energy transmission x-ray target follows a similar general approach throughout the literature, the specific methodology can vary substantially. The goal of this study was to determine the sensitivity of x-ray target optimization to different methods of x-ray quantification and temperature modeling.<i>Approach.</i>Ultrathin (1.5- to 90-m) tungsten transmission x-ray targets were modeled in TOPAS (v.3.8) and bombarded with electrons at energies of 100-500 keV. Simulations were run to compare the optimal target thickness according to various tallies of the emitted x-ray field, including primary beam fluence, energy fluence, air KERMA, dose to water in air, or dose to water at depth in phantom. The optimized targets for each energy were simulated again to calculate the spatial distribution of heat deposited within the target and the attached diamond or copper window. Finally, COMSOL Multiphysics® was used to compare temperature calculations with a volumetric heat source model versus a simplified surface heat source model.<i>Main results.</i>The target thickness optima varied significantly across the different x-ray quantities; whereas some metrics favored very thin targets (<10m) for higher, low-quality x-ray output, others favored thicker targets (>50m) weighted towards higher-energy x-ray fields. Heat calculations in the optimized targets showed that single-scattering Monte Carlo produced a greater energy deposition tally compared to multiple-scattering models. Lastly, finite element temperature calculations did not change significantly between the full spatial heat deposition model and the simplified surface heat source model.<i>Significance.</i>This study demonstrates the importance of selecting the proper quantity for target optimization to ensure the most translatable results for the device's intended use. This work also shows that temperature modeling can be greatly simplified to accelerate the design process while maintaining computational accuracy. The data presented here represent an important resource in transmission x-ray target modeling.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148913137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Model-based motion simulation framework for deep learning-assisted motion correction in dynamic wrist CT.","authors":"Chunming Gu, Aeden K Davis, Andrew R Thoreson, Shengbing Huang, Kevin Treb, Nirusha Lachman, Kristin D Zhao, Maryam Sadeghian, Francis Baffour, Taylor P Trentadue, Sanjeev Kakar, Cynthia H McCollough, Shuai Leng, Hao Gong","doi":"10.1088/1361-6560/aea684","DOIUrl":"10.1088/1361-6560/aea684","url":null,"abstract":"<p><p><i>Objective.</i>Four-dimensional CT (4DCT) enables visualization of dynamic wrist joint pathology but may be compromised by motion artifacts. Deep learning (DL)-assisted motion correction has the potential to enhance wrist 4DCT quality, but model development is hindered by scarce training data. To address this, we developed a model-based motion simulation framework that generated realistic 4DCT data with paired static ground truth images to demonstrate wrist motion correction using a physics-informed DL model trained with simulated data.<i>Approach.</i>Wrist motion was simulated by synchronizing rotational and translational movements of carpal bones and connective tissues. Elastic deformation guided by analytically-derived motion vector fields was applied to static wrist scans at neutral positions to create artifact-free images at multiple angular positions. Virtual motion-corrupted 4DCT images were produced via forward projection and reconstruction with synchronized gantry and wrist motion. Experimental data from 4DCT cadaver scans were collected to validate simulation quality. Low-intensity region score (LIRS), positivity, and entropy were used to assess simulated motion artifacts. A physics-informed motion correction network was adapted exclusively using simulated training data and subsequently deployed on simulated, real cadaveric, and<i>in vivo</i>4DCT scans. LIRS and structural similarity index (SSIM) were used to evaluate motion correction quality. Wilcoxon signed-rank tests were conducted (<i>α</i>= 0.05).<i>Results.</i>The simulation method created realistic motion artifacts compared to real scan reference (<i>p</i>> 0.05). Motion artifacts were effectively mitigated across testing cases demonstrating generalizability. In simulated scans, LIRS improved from 0.55 ± 0.12-0.75 ± 0.04 and SSIM from 0.87 ± 0.08-0.95 ± 0.03 at bone regions (each<i>p</i>< 0.01). In experimental cadaveric scans, LIRS improved from 0.05 ± 0.01-0.31 ± 0.17 in marker regions and from 0.58 ± 0.19-0.77 ± 0.14 in bone regions (each<i>p</i>< 0.01).<i>Significance.</i>Our simulation method facilitates training DL-assisted motion correction algorithms by providing high-quality training data, effectively supporting 4DCT image quality enhancement.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13652031/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148945635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preclinical application and evaluation of an energy-based spectral unmixing method for multi-radionuclide SPECT.","authors":"Matthew Strugari, Sam Porter, Kris Thielemans, Kimberly D Brewer","doi":"10.1088/1361-6560/aeac98","DOIUrl":"https://doi.org/10.1088/1361-6560/aeac98","url":null,"abstract":"<p><p><i>Objective.</i>Crosstalk poses significant challenges in multi-radionuclide SPECT, where γ-rays from one radionuclide are incorrectly attributed to a different radionuclide, compromising image fidelity and interpretations. Although the triple energy window (TEW) method is widely accepted for correcting crosstalk in the acquired energy spectrum, its effectiveness depends on the gamma camera's energy resolution and statistical counts on a pixel-by-pixel basis. Furthermore, subtractive corrections applied before image reconstruction, such as TEW, alter the Poisson distribution of detected events, negatively impacting statistical reconstruction accuracy, reconstructed image noise, and image quality. To address these challenges, we introduce an energy-based spectral unmixing crosstalk correction approach in a preclinical setting using the open-source Synergistic Image Reconstruction Framework (SIRF) and Core Imaging Library (CIL). This method employs a mixing matrix to decompose hyperspectral data into distinct radionuclide distributions during synergistic reconstruction. &#xD;<i>Approach.</i>Data were acquired with the Cubresa Spark preclinical SPECT scanner using^99mTc/¹²³I in measurement and simulation, and^99mTc/¹¹¹In in simulation. A mouse-sized phantom study employed five 4 MBq line sources with linearly varying mixtures of radioactivity. The images were reconstructed using primary energy windows, TEW, spectral unmixing, and gold standard simulation data representing activity distributions free of crosstalk. Performance evaluation used root-mean-square error (RMSE) for activity quantitation and image contrast, while noise was assessed separately in each image.<i>Main results.</i>In the^99mTc/¹²³I measurement, primary energy windows yielded a mean quantitation RMSE of 0.49, with improvements of 32% observed with TEW and 74% with spectral unmixing. Simulation results were consistent, giving an RMSE of 0.44 for primary energy windows, with improvements of 51%, 83%, and 95% observed with TEW, spectral unmixing, and gold standard methods. For the^99mTc/¹¹¹In simulation, the mean quantitation RMSE was 0.15 with primary energy windows, while TEW, spectral unmixing, and gold standard methods improved accuracy by 57%, 57%, and 84%, respectively. Across all cases, spectral unmixing also demonstrated superior contrast and reduced noise compared to TEW.<i>Significance.</i>This energy-based spectral unmixing approach provides enhanced crosstalk correction, quantitative accuracy, and image quality compared to conventional methods, facilitating flexible application in diverse SPECT systems and radionuclide combinations.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149063446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PKiNN: a PET kinetics-informed neural network for dynamic PET kinetic modeling.","authors":"Chunmeng Tang, Koen Van Laere, Michel Koole","doi":"10.1088/1361-6560/aea39a","DOIUrl":"10.1088/1361-6560/aea39a","url":null,"abstract":"<p><p><i>Objective.</i>Voxel-wise PET kinetic modeling of dynamic PET data enables the generation of quantitative parametric maps reflecting tracer kinetics, but it is computationally demanding and sensitive to noise. This study investigated whether embedding the underlying kinetic model of PET tracer behavior into a neural network framework (PET kinetics-informed neural network, PKiNN) improves voxel-wise parameter estimation compared with conventional linearized approaches.<i>Approach.</i>PKiNN, a recurrent neural network with long short-term memory (LSTM), was trained on simulated time-activity curves generated using a one-tissue compartment model (1TCM) with randomized kinetic parameters spanning physiologically plausible ranges. A kinetics-informed loss term was incorporated into the network loss function to constrain the predicted parameters. A baseline neural network (NN-LSTM) without the kinetics-informed loss was also trained for comparison. Performance was assessed across multiple simulated noise levels and using clinical¹¹C-UCB-J PET data. A supplementary simplified reference tissue model (SRTM) implementation was evaluated as a proof of concept.<i>Main results.</i>Across all simulated noise levels, PKiNN consistently outperformed NN-LSTM, yielding lower relative error (RE, %) and absolute relative error (ARE, %) for,, and. For example, at an SNR of 20 dB, the REs and AREs forestimated by NN-LSTM wereand, respectively, while for thederived from PKiNN, RE and ARE wereand, respectively. For clinical¹¹C-UCB-J PET data, PKiNN-derived voxel-wise maps showed close agreement with VOI-based 1TCM fitting, minimal bias inand, modest overestimation of, and reduced underestimation compared with Logan graphical analysis.<i>Significance.</i>Overall, PKiNN provides a fast, accurate, and noise-robust alternative to conventional 1TCM kinetic modeling, demonstrating feasibility for clinical PET, and the supplementary SRTM proof-of-concept provides preliminary evidence of its potential for extension to other kinetic models.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148907005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Conditional diffusion models for high-fidelity synthetic CT generation from CBCT in nasopharyngeal carcinoma adaptive radiotherapy: a multi-center study.","authors":"Hui Xie, Hao Chen, Qiwei Li, Zijie Chen, Yue Sun, Tao Tan","doi":"10.1088/1361-6560/ae98db","DOIUrl":"10.1088/1361-6560/ae98db","url":null,"abstract":"<p><p><i>Objective.</i>To develop and validate a conditional diffusion probabilistic model (cDDPM) for generating high-quality synthetic CT (sCT) from cone-beam CT (CBCT) to support accurate online adaptive radiotherapy (ART) for nasopharyngeal carcinoma (NPC).<i>Approach.</i>Planning CT (pCT) and CBCT images from 1128 NPC patients across two independent centers were retrospectively analyzed. After rigid and deformable registration and preprocessing, 626 cases were used for training, 267 for internal testing, and 235 from another center for external validation. The proposed cDDPM was compared with VAE, GAN, unconditional DDPM, Swin-UNet and latent diffusion model (LDM). Image quality and dosimetric accuracy of sCT were comprehensively evaluated.<i>Main results.</i>In both internal and external validation cohorts, cDDPM-generated sCT significantly outperformed all competing methods across all metrics (MAE, SSIM, MS-SSIM, PSNR, PSNR-hvs, PSNR-hvs-m; all), while showing no significant difference from pCT (all). Mean dose differences for target volumes and critical organs at risk were0.4and1.6, respectively, with no statistical significance. 3D gamma passing rates (3 mm/3) exceeded 98.0in both cohorts.<i>Significance.</i>The proposed cDDPM generates sCT images with image quality approaching that of pCT and introduces negligible dosimetric uncertainty. While prospective clinical validation is still required, the model demonstrates strong potential to facilitate safe and efficient online ART in NPC.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148723638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High spatial resolution dual-ended readout PET detector based on continuous resistive layer silicon photomultiplier.","authors":"Jiahao Xie, Haibo Wang, Junwei Du","doi":"10.1088/1361-6560/ae9a28","DOIUrl":"10.1088/1361-6560/ae9a28","url":null,"abstract":"<p><p><i>Objective.</i>Continuous resistive layer position-sensitive silicon photomultiplier (CRL PS-SiPM) is a class of position-sensitive SiPMs developed for the readout of fine-pitch scintillator crystal arrays. This study aimed to evaluate the performance of dual-ended readout positron emission tomography (PET) detectors based on CRL PS-SiPMs and 0.5 mm pitch LYSO arrays.<i>Approach.</i>A dual-ended readout detector was constructed by coupling two CRL PS-SiPMs to both ends of a 10 × 10 array of polished LYSO elements, each measuring 0.44 × 0.44 × 20 mm³. Each CRL PS-SiPM had an active area of 6.24 × 6.24 mm²and was fabricated using 20<i>µ</i>m microcells. Detector performance, including flood histogram quality, energy resolution, and coincidence timing resolution (CTR), was characterized at bias voltages ranging from 30.0 to 33.0 V in 0.5 V increments, and at 3<b>°</b>C, 14<b>°</b>C, and 24<b>°</b>C. Depth-of-interaction (DOI) resolution was evaluated at the optimal bias voltage determined from the flood histogram and at all three temperatures.<i>Main results.</i>Temperature had a negligible effect on detector performance, indicating that CRL PS-SiPMs are practical photodetector candidates for high spatial resolution PET scanners. All LYSO crystals were clearly resolved in the flood histograms. At 24<b>°</b>C and a bias voltage of 32.5 V, which provided the best flood histogram, the average energy resolution, CTR, and DOI resolution across all crystals were 22.7 ± 3.4%, 1152 ± 43 ps, and 1.78 ± 0.20 mm, respectively.<i>Significance.</i>These results demonstrate that CRL PS-SiPMs are promising photodetectors for high spatial resolution PET applications, particularly for systems requiring detectors with sub-millimeter pitch scintillator crystal arrays and DOI capability.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148765248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessment of elemental decomposition algorithms for particle therapy dose monitoring using positron emission tomography and prompt-gamma imaging.","authors":"Yan Li, Weiguang Li, Xin-Yu Hu, Yu-Ying Yin, Xueying Yang, Shutong Yu, Chao Yang, Cheng Chang, Mingqing Wang, Kai-Wen Li, Li-Sheng Geng, Yibao Zhang","doi":"10.1088/1361-6560/aea1d4","DOIUrl":"10.1088/1361-6560/aea1d4","url":null,"abstract":"<p><p><i>Objective.</i>Accurate dose verification remains a major challenge in particle therapy. Dose monitoring methods such as positron emission tomography (PET) and prompt-gamma (PG) imaging are highly sensitive to uncertainties in tissue composition derived from CT, which can be improved by dual-energy CT (DECT)-based material decomposition. This study systematically assessed the accuracy of four DECT elemental decomposition algorithms in predicting physical dose, annihilation-photon, and PG reference distributions in particle therapy, focusing on CT-based model uncertainty without detector considerations.<i>Approach.</i>Three parameterization-based DECT methods, a machine-learning (ML) DECT method, and a conventional single-energy CT (SECT) method were used to predict the elemental composition of the ICRP110 human phantom and 10 head-and-neck patients. The physical dose, annihilation, and PG distributions for incident proton, helium, carbon, and oxygen pencil beams were compared using Monte Carlo simulations. For the phantom, mean relative errors (MREs) were calculated relative to the reference distributions. For the patients, the distal fall-off positions of annihilation and PG profiles were compared across the methods.<i>Main results.</i>In the phantom study, the ML method yielded the lowest MREs across the four incident particle types. For oxygen ions, the ML method yielded an annihilation-photon MRE of 2.64%, compared with 6.50%-6.74% for the parameterization-based DECT methods. The corresponding PG MRE were 1.53%, 2.44%-2.60% for the ML and parameterization-based methods. The matched SECT analysis provided a conventional baseline under the same simulation and evaluation settings. In the patient analyses, the distal fall-off positions of annihilation and PG differed by up to 1.93 ± 0.42 mm and 1.76 ± 0.44 mm, respectively, between ML and the parameterization-based methods. Without voxel-wise patient ground truth, these results describe inter-method differences rather than an accuracy ranking.<i>Significance.</i>Compared with the parameterization-based methods, the ML method reduced errors in predicting source-level PET and PG reference distributions under the idealized Monte Carlo conditions used here, especially for heavier incident particles. These results quantify model-related uncertainty in complementary with detector resolution in clinical monitoring accuracy.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148881555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Intracavitary electron radiotherapy with dynamic shielding for rectal cancer: applicator design and dosimetric characterization.","authors":"Jinghui Wang, Mingqing Wang, Heming Wang, Jianfeng Lv, Bin Liu, Qiheng Li, Dongna Li, Da Fu, Kai Wang, Dongpo Fu, Hanxiang Du, Xin Xia, Bo Ma, Chaohui Ran, Wenbing Yan, Wei Gai, Kun Zhu, Hao Wang, Xueqing Yan","doi":"10.1088/1361-6560/aea5ce","DOIUrl":"10.1088/1361-6560/aea5ce","url":null,"abstract":"<p><p><i>Objective.</i>Intensity-modulated brachytherapy can improve dose conformity for rectal cancer, but current¹⁹²Ir-based systems are limited by isotropic photon emission, sequential shield motion, treatment-time penalties, and radioisotope logistics. This study designed, optimized, and characterized a dynamically shielded applicator-based intracavitary electron radiotherapy system intended to improve dose localization and enable ultra-high dose-rate (HDR) delivery without a radioactive source.<i>Approach.</i>A cylindrical electron-beam applicator was designed with a high-density shield containing an emission window, a low-<i>Z</i>scatterer, and a polycarbonate guide tube. Applicator geometry was optimized using TOPAS Monte Carlo simulations to minimize radial and distal transmission factors (TF_radialand TF_distal). Dosimetric performance was benchmarked against a modified Monte Carlo model based on a commercial¹⁹²Ir shielded rectal applicator (Varian GM11004160). A 3D-printed prototype with a stainless-steel shield and resin components was experimentally evaluated using a custom linear accelerator (5 MeV nominal energy, 60 mA peak current, 4<i>μ</i>s pulse width). Dose distributions were measured with EBT-XD radiochromic film.<i>Main results.</i>In the modeled homogeneous benchmark geometry, the optimized tungsten applicator achieved a radial transmission factor of approximately 1% at 10 mm from the applicator surface, compared with approximately 20% for the modeled¹⁹²Ir reference system. Distal leakage remained below 5% beyond the applicator distal end. Under modeled accelerator conditions, the electron-beam system reached approximately 100 Gy s^-1at 100 Hz. Superposition of single-dwell dose kernels produced both uniform fields and spatially fractionated radiotherapy patterns with valley-to-peak dose ratios ⩽ 0.2. Prototype measurements demonstrated localized directional dose delivery and ultra-high mean dose rates under the reported pulse conditions, while identifying leakage pathways that caused order-of-magnitude differences from simulation.<i>Significance.</i>The optimized Monte Carlo model demonstrated improved radial dose localization,radioisotope-free operation, and ultra-HDR capability in homogeneous geometry. Further work is needed for accelerator integration, motion control, inverse planning, and validation in anatomically realistic settings.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148930346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}