Physics in medicine and biology最新文献

{"title":"Deformable 3D dosimetry of MRI-tracking radiotherapy.","authors":"Morgan J Wheatley, Jarrad Begg, Yves De Deene","doi":"10.1088/1361-6560/ae674a","DOIUrl":"https://doi.org/10.1088/1361-6560/ae674a","url":null,"abstract":"<p><p>During breathing, anatomical structures within the torso move which can result in inaccurate radiation dose delivery. With the introduction of MRI-linear accelerators (MRI-linacs), the ability to simultaneously acquire high-contrast soft tissue images during irradiation allows for compensation of intrafraction motion and deformation by gating or tracking the target volume. The implementation of MRI-guided tracking radiotherapy is not without risks as any lag or organ deformation may not be accounted for. Polymer gel dosimetry has the potential to measure the integral dose delivered to deforming and moving targets as the gels are flexible and provide a high-resolution 3D dose profile. &#xD;Spherical silicone casts filled with polymer gel and silica beads were compressed to measure the deformation of gel phantoms. The effect of compression on the dose response was studied by irradiating and scanning the spherical phantoms in various states of compression. End-to-end gel dosimetry experiments with MRI-guided tracking radiotherapy were conducted on a prototype MRI-linac (Australian MRI-Linac) using a moving, non-deformable, rectangular-shaped gel dosimeter phantom and an MRI-safe, pneumatically actuated, anthropomorphic, breathing phantom containing a liver-shaped gel dosimeter. Radiochromic film dosimeters within the phantoms were used as secondary validations of the dose profile. The tracking performance of the MRI-linac was assessed by comparing measured dose distributions in the phantoms in static and actuated experiments.&#xD;There was no significant impact of compression on the dose response in the irradiated spheres. The gel-measured dose profiles in the phantoms matched closely with the film dosimeters for tracked and non-tracked scenarios. The end-to-end gel dosimeter experiments illustrate the improvement in dose conformality with MRI-guided tracking. &#xD;Deformable 3D gel dosimeters in an anthropomorphic body phantom can be used for assessing 3D geometric accuracy of tracked treatments on MRI-linacs, but care should be taken to account for the oxygen inhibition at the edges of the dosimeter.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147819364","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":"Comparison of physical approaches to inter-crystal scattering in a staggered-layer scintillation PET detector: a simulation study.","authors":"Qi Liu, Juergen J Scheins, Elisabeth Pfaehler, Keith George Ciantar, Debora Niekämper, Cláudia Régio Brambilla, Qingxian Zhang, Nadim Jon Shah, Christoph W Lerche","doi":"10.1088/1361-6560/ae674b","DOIUrl":"https://doi.org/10.1088/1361-6560/ae674b","url":null,"abstract":"<p><strong>Objective: </strong>Inter-crystal scattering (ICS) degrades spatial resolution and contrast by causing spurious lines of response in small-pitch, staggered three-layer pixelated LSO scintillation detectors used in a high-resolution BrainPET-7T insert. This work aimed to investigate the distribution of ICS events in our BrainPET-7T detector and understand its underlying mechanisms.</p><p><strong>Approach: </strong>Six physical approaches for computing probabilities to identify the first interaction positions of ICS events were studied using Geant4 simulations, focusing specifically on events with two interactions, which represent the most frequent ICS occurrence. Performance was evaluated using ideal interaction positions and energies directly from simulations, ground truth crystal-center positions with ideal energies, as well as crystal-center positions and energies determined by a maximum likelihood positioning (MLP) algorithm.</p><p><strong>Main results: </strong>A method based on Klein-Nishina probabilities, which were computed using geometric information (KN-G) and MLP-derived crystal-center positions and energies, achieved superior accuracy, particularly when the distance between successive interactions in Compton events was shorter than 6 mm and when incident angles were below 15 • . This advantage is partly attributable to crystal-center discretization, which masks a substantial portion of backscattering events. It reached a peak accuracy of 92.2 % at a distance of 19 mm.</p><p><strong>Significance: </strong>These findings demonstrate the feasibility of combining the KN-G method with the MLP algorithm to mitigate the ICS effects, with the potential to improve the image quality of the 7T BrainPET insert.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147819388","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":"Microdosimetric kinetic model for enhanced estimation of cell survival in aerobic human salivary gland cells under heavy ion irradiation.","authors":"Tae Ho Jang, Hyung Jin Choun, Eun Taek Yoon, Sung Hyun Lee, Jong Min Park","doi":"10.1088/1361-6560/ae5d82","DOIUrl":"10.1088/1361-6560/ae5d82","url":null,"abstract":"<p><p><i>Objective.</i>Accurate estimation of cell survival fractions across a broad range of linear energy transfer (LET) is essential for precise heavy ion therapy planning. The microdosimetric kinetic (MK) model predicts cell survival from microdosimetric quantities; however, most closed-form MK formulations treat the quadratic coefficientβas a constant, which limits predictive accuracy under high-LET irradiation. This study aimed to develop a revised MK model that overcomes this limitation by redefiningβas an LET-dependent function.<i>Approach.</i>The revised MK model incorporates the saturation-corrected dose-mean specific energy into the formulation ofβ. Model performance was evaluated against the reference MK model using 324 reconstructed survival fraction data points from 54 irradiation conditions of aerobic human salivary gland tumor cells exposed to helium, carbon, and neon ions. Parameter estimation was performed using a log-scaled mean squared error loss optimized through a hybrid global-local scheme.<i>Main results.</i>At low LET, both the revised and reference models reproduced experimental survival with comparable accuracy. However, at higher LET, the revised model maintained stable agreement with experimental data, whereas the reference model diverged markedly due to excessive curvature in its predictions. Across the entire experimental LET range, the revised model consistently reproduced cell survival data more accurately than the reference model.<i>Significance.</i>These findings demonstrate that redefining the quadratic coefficient as an LET-dependent term substantially improves the predictive accuracy of the MK model under high-LET and wide-dose conditions. The proposed model enhances radiobiological modeling performance while preserving the structural simplicity and compatibility of the existing MK framework.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147646155","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":"FLIP-HEDOS: a patient-specific blood dose quantification model during radiotherapy treatments.","authors":"Marina García-Cardosa, Chris Beekman, Javier Burguete, Harald Paganetti","doi":"10.1088/1361-6560/ae6015","DOIUrl":"10.1088/1361-6560/ae6015","url":null,"abstract":"<p><p><i>Objective.</i>To introduce FLIP-HEDOS, a blood dose modeling framework that combines patient-specific and generic circulatory data to enable individualized blood dose estimation during radiotherapy (RT) treatments and to overcome limitations of non-personalized approaches.<i>Approach.</i>Patient-specific images of vasculature were obtained from patients with thorax-abdomen or head-neck tumors treated with proton or photon RT. Large vessels from the tumor location were segmented, and their blood flow velocities were extracted from phase-contrast MRI. Movement of blood particles (BPs) was simulated using a Lagrangian approach along patient-specific flowlines in these vessels, forming the FLIP method. This circulation was incorporated into a standardized model (HEDOS) to form a closed-loop whole-body model that computes the spatiotemporal BP distribution and associated blood dose accumulation, accounting for dose delivery dynamics, dose rate and beam-on/beam-off times. Cardiac output (CO) was individualized to match each patient blood flow characteristics. FLIP-HEDOS retains the modular HEDOS architecture, extending its large vessel compartments with the FLIP approach patient-specific vessels represented as new compartments. Remaining compartments were adapted to preserve the standardized connectivity of the circulatory network.<i>Main Results.</i>The study quantified mean blood dose values and tracked the number of times BPs entered patient-specific compartments during dose delivery. Simulations were performed across a range of inter-beam intervals, and the three models FLIP (patient-specific vessels), HEDOS (generic whole-body), and FLIP-HEDOS (integrated model) were compared with respect to their resulting blood dose values. The comparison shows that when patient-specific information is incorporated in blood dose assessment, BPs experience higher radiation doses.<i>Significance.</i>FLIP-HEDOS proves that standardized vascular data can be effectively combined with patient-specific parameters to achieve physiologically realistic modeling of circulating blood. By enabling individualized CO and blood flow dynamics, the framework adapts to the anatomical and hemodynamic characteristics of each patient.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147691541","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":"Deducing cardiorespiratory motion of cardiac substructures using a novel 5D-MRI workflow for radiotherapy.","authors":"Chase Ruff, Tarun Naren, Oliver Wieben, Prashant Nagpal, Kevin Johnson, Jiwei Zhao, Thomas Grist, Andrew Baschnagel, Carri Glide-Hurst","doi":"10.1088/1361-6560/ae5752","DOIUrl":"10.1088/1361-6560/ae5752","url":null,"abstract":"<p><p><i>Objective.</i>Cardiotoxicity is a devastating complication of thoracic radiotherapy. However, current practice ignores the radiosensitivities and complex motion trajectories of individual substructures. Current imaging protocols in radiotherapy are insufficient to decouple and quantify cardiac motion, limiting substructure-specific motion considerations in treatment planning. We propose a 5D-MRI workflow for comprehensive substructure-specific motion analysis.<i>Approach.</i>Our 5D-MRI workflow was implemented in 10 healthy subjects (23-65 years) and two patients with lung cancer (67-69 years), with iterative reconstruction at end-exhale/inhale and active-exhale/inhale for end-systole/diastole. For motion assessment, proximal coronary arteries, chambers, great vessels, and cardiac valves/nodes were contoured across all images and verified. Centroid/bounding box excursion was calculated for cardiac, respiratory, and hysteresis motion. Distance metrics were tested for statistical independence across substructure pairings. Three thoracic radiotherapy plans were retrospectively analyzed using volunteer-derived internal organ-at-risk volumes (IRVs). Cardiac substructure motion was compared between volunteer and patient cohorts.<i>Main results.</i>5D-MRI images were successfully acquired and contoured for all volunteers. Cardiac motion exceeded 1 cm for right-heart substructures and was greatest for the right coronary artery. Respiratory motion was largest for the inferior vena cava/left ventricle. Respiratory hysteresis was generally <5 mm but >5 mm for some subjects. For cardiac motion, statistically significant differences were observed between coronary arteries/chambers/great vessels and between right/left-sided substructures. Respiratory motion differed significantly between the heart base/apex. For three plans, D_0.03ccincreased by up to 21.5 Gy across volunteer-derived cardiorespiratory IRVs. Patients' right-heart motion ranged from 7-19 mm, yet left-heart motion varied due to tumor location.<i>Significance.</i>Our 5D-MRI workflow successfully decouples cardiorespiratory motion in a ∼5 min free-breathing acquisition. Cardiac motion was >5 mm for coronary arteries/chambers, while respiratory motion was >5 mm for all substructures. Statistically significant differences were observed between cardiac substructures for cardiac and respiratory motion. The interplay between tumor location and motion magnitude affected substructure dose.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13125878/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147514153","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":"[177Lu]Lu-PSMA extravasation: from quantitative imaging to clinical guidelines.","authors":"Julien Salvadori, Oreste Allegrini, Ritzenthaler Florian, Nathan Poterszman, Clemence Porot, Xavier Malezieux, Melody Potel, Francois Somme","doi":"10.1088/1361-6560/ae6014","DOIUrl":"10.1088/1361-6560/ae6014","url":null,"abstract":"<p><p><i>Objective.</i>Extravasation of therapeutic radioligands such as [177Lu]Lu-PSMA-617 or [177Lu]Lu-DOTATATE is rare but may result in localized radiation injury. In the absence of standardized guidelines, management remains empirical. We describe two cases of [177Lu]Lu-PSMA extravasation, evaluated using a fully automated, time-resolved dosimetric workflow supporting evidence-based conservative management.<i>Approach.</i>Two patients exhibiting localized extravasation were treated using conservative measures, including manual massage, warmth application, and arm elevation. Clearance kinetics were assessed using quantitative SPECT/CT, comprising 3-4 early acquisitions within 6 h, followed by imaging at 24 h and >48 h. Absorbed doses were calculated within threshold-based sub-volumes (ranging from <1 ml to the full volume) using mono-exponential fitting. Systemic dosimetry of organs at risk and metabolic tumor volume (MTV) was assessed in both patients and, for one patient, compared across extravasated and uneventful cycles. The analytical pipeline incorporated deep learning-based CT segmentation, anatomy-guided partial volume correction, Monte Carlo-derived dose computation, and compartment-specific kinetic modeling.<i>Main results.</i>Both patients demonstrated rapid clearance of extravasated activity, with effective half-lives of 1.42 h and 1.52 h. Even the most highly irradiated sub-volumes (<1 ml) received <10 Gy, far below necrosis thresholds. During extravasated cycles, renal absorbed doses exceeded 1 Gy, while MTV doses reached 32.1 Gy and 9.6 Gy, respectively. In Patient 1, systemic dosimetry was nearly identical between extravasated and subsequent cycles (<10% variation for kidneys). The only substantial change was a decline in MTV dose (32.1 → 20.2 Gy), consistent with declining tumor uptake over successive [177Lu]Lu-PSMA administrations.<i>Significance.</i>[177Lu]Lu-PSMA extravasation undergoes rapid clearance under conservative management, with absorbed doses below deterministic thresholds and unaffected systemic biodistribution. Conservative interventions-massage, warming, and arm elevation are therefore justified. Automated quantitative dosimetry enables same-day dose estimation, providing an objective basis for timely clinical decision-making and paving the way toward standardized management protocols.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147691436","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":"Robust optimized dynamic mixed-beam arc radiotherapy for left-sided breast radiotherapy under deep inspiration breath-hold variations.","authors":"Björn Zobrist, Werner Volken, Hannes A Loebner, Chengchen Zhu, Silvan Mueller, Peter Manser, Michael K Fix, Jenny Bertholet","doi":"10.1088/1361-6560/ae6019","DOIUrl":"10.1088/1361-6560/ae6019","url":null,"abstract":"<p><p><i>Objective.</i>Dynamic mixed-beam arc radiotherapy (DYMBARC) combines intensity-modulated electron- and photon-arcs in order to reduce normal tissue dose compared to photon-only techniques while ensuring similar target coverage. For left-sided breast, deep inspiration breath-hold (DIBH) improves heart sparing and mitigates breathing motion. However, dose delivery uncertainties remain due to inter- and intra-breath-hold variations. We assess robustness and dosimetric plan quality of robust optimized (RO)-DYMBARC under DIBH variations with comparison to volumetric modulated arc therapy (VMAT).<i>Approach.</i>Ten cases were created using the extended cardiac-torso anthropomorphic phantom. NiftyReg was used to obtain deformation vector fields (DVFs) for DIBH variations. For each case, three plans were created: planning target volume (PTV)-based VMAT, RO-VMAT, and RO-DYMBARC, prescribed 42.4 Gy to the target volume (PTV or clinical target volume for RO plans). Robustness to DIBH variations was assessed by recalculating doses using the DVFs and deformable voxel geometry Monte Carlo simulations. Dosimetric endpoints for targets and organs at risk (OARs) were compared using Wilcoxon matched-pair signed-rank test (<i>α</i>= 0.05).<i>Main results.</i>RO-DYMBARC demonstrated significantly better OAR sparing compared to VMAT, with mean dose to heart and contralateral breast up to 1 Gy lower than PTV-based VMAT. Target coverage and robustness to DIBH variations were similar across all plans. For OARs, DIBH variations led to dose differences⩽ 0.1 Gy for all plans and endpoints compared to the nominal scenario.<i>Significance.</i>RO-DYMBARC provided superior dosimetric plan quality with similar robustness to DIBH variations compared to VMAT. The dosimetric advantage of RO-DYMBARC was maintained in the presence of DIBH variations.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147691622","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":"Prior-guided craniofacial soft-tissue reconstruction from CBCT under acquisition uncertainty via identity-quantized shape priors.","authors":"Mingzhang Chen, Jiasong Wu, Luwei Liu, Han Bao, Ye Cao, Qingmo Sun, Lotfi Senhadji, Huazhong Shu, Bin Yan","doi":"10.1088/1361-6560/ae5ebc","DOIUrl":"10.1088/1361-6560/ae5ebc","url":null,"abstract":"<p><p><i>Objective.</i>Cone-beam computed tomography (CBCT) suffers from low soft-tissue contrast and metal artifacts, yielding noisy and incomplete soft-tissue surface observations that limit craniofacial modeling for surgical planning. This study aims to reconstruct identity-preserving facial soft-tissue surfaces from CBCT-derived sparse surface evidence for clinical decision support.<i>Approach.</i>We propose a prior-guided reconstruction framework that introduces identity quantization as an<i>anatomical</i>shape prior to regularize an inherently underdetermined inference problem. By embedding residual vector quantization within a hierarchical encoder, we learn a discrete identity codebook that improves robustness to acquisition-induced outliers and missing regions while preserving patient-specific anatomical structure. A continuous style branch captures fine-scale details, and the two representations are fused to generate detailed meshes.<i>Main results.</i>Evaluation on 490 subjects, including 50 test cases, shows that our method achieves a 34-point landmark distance of 1.53 mm. Geometric accuracy (GA) is confirmed with an L1 Chamfer distance of 1.13 mm and normal consistency of 0.98. A prospective expert study reveals high clinical acceptance, with GA rated 4.27 ± 0.53 (out of 5).<i>Significance.</i>By incorporating an explicit anatomical prior to regularize reconstruction under acquisition uncertainty, our method improves the clinical usability of CBCT-based soft-tissue surface modeling for orthognathic surgery planning.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147675564","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":"Micro CT calibration accuracy for pre-clinical studies in ion therapy.","authors":"A Bückner, M Moglioni, U Weber, L Volz, O Sokol, M Witt, M Simard, M Durante, D Boscolo","doi":"10.1088/1361-6560/ae5ebb","DOIUrl":"10.1088/1361-6560/ae5ebb","url":null,"abstract":"<p><p><i>Objective.</i>Accurate estimation of tissue stopping power ratios (SPRs) from computed tomography (CT) data is essential in charged particle therapy (CPT), yet it remains a major source of range uncertainties. While various SPR calibration methods have been developed for clinical CT scanners, they are not tailored to cone beam type Micro CT scanners commonly used in pre-clinical studies involving small animals. This work aims to assess how different clinical SPR calibration methods influence range predictions in small animal CPT pre-clinical trials, evaluated at both the voxel and organ levels.<i>Approach.</i>A small animal calibration phantom was imaged with a Micro CT at x-ray tube voltages between 45 kV and 70 kV. The images were used in two single energy (SECT), a stoichiometric and a simplified method, and one stoichiometric dual energy (DECT) calibration method. The accuracy of SPR predictions for each method was evaluated using simulated CT images of murine head, thorax, and abdomen virtual phantoms derived from<i>in vivo</i>data.<i>Main results.</i>Both SECT methods were found to yield comparable accuracy in the head and abdomen areas. Root mean squared (RMS) errors to the nominal SPR values were found to be 5.04% and 4.22% in the head phantom and 2.31% and 2.61% in the abdomen phantom, for the stoichiometric and simplified SECT method, respectively. RMS errors in the lung phantom were found to be 16.42% and 35.80%. The stoichiometric DECT method was found to improve accuracy in the lung phantom to 12.37% while in the head phantom it achieved 19.37% and in the abdomen 6.42%.<i>Significance.</i>This is the first report of treatment plan agnostic low-kV Micro CT SPR calibration accuracy. It can provide a reference for expected SPR and range uncertainties in pre-clinical CPT trials.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147675484","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":"Relevance of the Radon space shadow zone in coplanar and non-coplanar volumetric modulated arc therapy: studies on head and neck and geometrical targets.","authors":"Gary Razinskas, Victor Lewitzki, Florian Exner, André Toussaint, Klaus Bratengeier","doi":"10.1088/1361-6560/ae5755","DOIUrl":"10.1088/1361-6560/ae5755","url":null,"abstract":"<p><p><i>Objective.</i>To investigate key geometrical sampling properties and potential advantages of non-coplanar volumetric modulated arc therapy (VMAT) compared with coplanar VMAT. The study is motivated by cone-beam computed tomography (CBCT) reconstruction theory, particularly concepts related to sampling completeness. The analysis focuses on head and neck cancers (HNC) and geometric phantoms.<i>Approach.</i>VMAT was simulated using densely spaced, fluence-optimised static beams. Non-coplanar partial arcs with angular ranges of 32°, 64°, or 180° centred at predefined gantry angles were added orthogonally to the standard coplanar circular beam arrangement, which served as the reference configuration. Plan quality was evaluated using the composite objective value, the minimum dose to the planning target volume (PTV), and the dose in cranio-caudal planes immediately adjacent to the PTV. The study included 20 patients with oro-, hypo-, or nasopharyngeal carcinomas with extended cranio-caudal target volumes (>15 cm) and complex anatomical organ at risk (OAR) proximity. In addition, idealised phantom cases (spherical or cylindrical PTVs with surrounding OAR structures) were analysed similarly to investigate controlled geometric configurations.<i>Main results.</i>Incorporation of non-coplanar arcs consistently improved plan quality. The most pronounced effect was observed for additional 180° arcs; however, even arcs with reduced angular range centred around the 0° gantry angle significantly increased PTV minimum dose while reducing dose to adjacent cranio-caudal tissues. These improvements are explained by the circle-and-arc beam configuration, which fulfils the Tuy condition known from CBCT theory by filling the Radon space shadow zone.<i>Significance.</i>Non-coplanar arcs with reduced angular ranges can enhance target coverage and organ sparing in elongated HNC targets. By transferring mathematical principles from CBCT reconstruction to radiotherapy planning, this work demonstrates how fulfilling the Tuy condition can improve VMAT dose distributions and may inform future developments in dynamic trajectory radiotherapy.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2026-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147514131","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}