Journal of Applied Clinical Medical Physics最新文献

Background: Computed tomography (CT) examinations of the head, paranasal sinus (PNS), and cervical spine (C-spine) are frequently performed in emergency settings, raising concerns about radiation exposure to the radiosensitive eye lens. Overexposure can cause radiation-induced ocular damage. To address this concern, organ dose modulation (ODM) has emerged as a promising technique for reducing eye lens dose in CT examinations.

Purpose: This study aimed to evaluate radiation exposure to the eye lens and objective image quality metrics for head, PNS, and C-spine CT examinations using fixed tube current, automatic tube current modulation (ATCM), and ODM techniques.

Methods: Eye lens doses were measured using nanoDot optically stimulated luminescence dosimeters (OSLDs) placed bilaterally to the eye lens of a whole-body anthropomorphic phantom (PBU-60). CT scans were performed using a Revolution EX CT scanner with three scanning techniques: fixed tube current, ATCM, and ODM. The phantom was scanned twice for each examination type (head, PNS, and C-spine) with all three techniques. Eye lens dose reductions with the ODM technique were quantified relative to fixed tube current and ATCM techniques. Image quality was quantitatively evaluated in terms of image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR).

Results: Mean eye lens doses ± standard deviation (SD) using the ODM technique were 38.44 ± 1.37, 17.92 ± 1.01, and 9.77 ± 0.38 mGy for head, PNS, and C-spine, respectively. These eye lens doses were reduced by 4.28%, 21.33%, and 47.97% compared to the fixed tube current techniques and by 19.40%, 24.70%, and 13.69% compared to the ATCM techniques, for head, PNS, and C-spine, respectively. These dose reductions were achieved while maintaining image quality metrics (image noise, SNR, and CNR) with no statistically significant differences (p > 0.05) compared to fixed tube current and ATCM techniques.

Conclusion: Implementation of the ODM technique resulted in significant eye lens dose reduction (4.28%-47.97%) across head, PNS, and C-spine CT examinations with no significant differences in image noise, SNR, and CNR compared to both fixed tube current and ATCM techniques. ODM demonstrates potential as a practical dose optimization strategy for routine emergency head and neck CT imaging. Further studies with subjective image quality assessment are recommended to evaluate clinical diagnostic acceptability in hospital settings.

Purpose: This study describes and evaluates the acceptance procedure for a ViewRay (VR) MRIdian 0.35T MR-Linac, emphasizing key challenges, limitations, and recommendations to enhance clinical performance and accuracy.

Methods: A comprehensive acceptance test was conducted at a single institution, following the manufacturer's protocols and aligned with established acceptance guidelines. Specific tools and phantoms were used to assess three primary components: mechanical, dosimetric, and Magnetic Resonance Imaging (MRI).

Results: Overall, the test outcomes satisfied the manufacturer's specifications. However, certain issues were identified: high couch attenuation at specific gantry angles (leading to their exclusion from treatment), variations in magnetic field homogeneity at different gantry angles, and discrepancies between TPS calculations and measurements for field output factors smaller than 0.83 cm × 0.83 cm.

Conclusion: This work provides a detailed account of the acceptance testing procedure and establishes a QA baseline for 0.35T MR-Linac systems. In doing so, it also identifies key system limitations, such as couch attenuation, magnetic field inhomogeneity, and small-field output discrepancies, underscoring the need for careful gantry angle selection, field homogeneity optimization, and meticulous validation of very small fields.

Purpose: Here we present an in-silico trial of the feasibility and deliverability of a same-day, simulation-free workflow for spatially fractionated adaptive radiotherapy (SF²-ART) using the Varian Ethos platform.

Methods and materials: Ten patients (five thoracic and five extremity), previously treated with spatially fractionated radiotherapy (SFRT), were selected for this in silico trial. A two-phase regimen was simulated: Phase 1 delivered 12 Gy SBRT to a uniform, predefined high-dose lattice and 4 Gy to the gross tumor volume (GTV); Phase 2 consisted of 4 additional fractions of 4 Gy to the GTV. The planning workflow was performed entirely in silico, without the need for CT simulation. High-dose sphere matrices were generated with a custom script and aligned to physician-defined GTVs. Adaptive plans were created based on CBCT anatomy and evaluated for dosimetric quality, deliverability, and workflow timing. Comparisons were made to the original clinically delivered plans. Mobius3D was used for secondary dose verification.

Results: All 10 cases were successfully replanned using the SF²-ART workflow without simulation-based imaging. The entire planning and treatment process, including consultation, contouring, adaptive plan generation, and QA, was performed within a single session. Dosimetric comparisons showed minimal differences between simulation-free adaptive and clinically delivered plans, with target coverage and normal tissue constraints maintained across all cases. Median total estimated workflow time was 166.4 min.

Conclusions: This in-silico study demonstrates the feasibility of delivering spatially fractionated SBRT without simulation CT using a same-day adaptive workflow. The SF²-ART approach may enable rapid, high-quality treatment for patients with urgent or symptomatic presentations and supports future prospective clinical implementation.

Background: In the IAEA TRS-483 Code of Practice (CoP), rectangular small field sizes are approximated to equivalent square small fields using the definition proposed by Cranmer-Sargison et al. However, the CoP estimates the uncertainties associated with this formula only for rectangular fields with dimensions within the range .

Purpose: The objective of the present study was to compare the accuracy of the Cranmer-Sargison definition with other formulas for equivalent square small fields in the context of measuring field output factors (FOFs) for rectangular small fields, both within and outside the range covered by the CoP.

Methods: Measurements were conducted using Gafchromic EBT4 radiochromic films. The models compared included Cranmer-Sargison, Sterling, Superellipse, Sterling-Partial Superellipse, Sterling-Superellipse, Vadash and Bjärngard, and Fogliata. The most accurate definition of equivalent square field size was identified as the one yielding the lowest discrepancy between measured and analytical values, with the log-likelihood of the measurements selected as the metric. Analytical values were derived using the function introduced by Sauer and Wilbert, which relates FOFs to equivalent square field sizes.

Results: The best results were achieved with the Fogliata model, followed in terms of accuracy by the Sterling-Partial Superellipse model. The Sterling-Superellipse and Vadash and Bjärngard models came next. It should be noted that the Sterling-Partial Superellipse and Sterling-Superellipse models rely solely on the geometric shape of the irradiation field size, whereas the Fogliata and Vadash and Bjärngard models incorporate a fitting parameter. The Sterling definition, while less accurate than these models, improved upon the Cranmer-Sargison definition and retained computational simplicity. Finally, the Cranmer-Sargison and Superellipse models exhibited the largest discrepancies.

Conclusions: This study identified several definitions of equivalent square small field size that could refine the IAEA TRS-483 CoP by improving the accuracy of field output correction factors for rectangular small fields. Among these definitions, the Fogliata model obtained the best results.

Background: Image-guided particle therapy (IGPT) has significantly advanced in recent years, particularly in the context of proton therapy. However, imaging solutions for carbon-ion radiotherapy (C-ion RT) remain limited.

Purpose: This study introduces sliding-gantry cone-beam computed tomography (CBCT) and dual-panel digital radiography (DR) systems, both mechanically independent of carbon-ion delivery nozzles. We aim to evaluate the image quality metrics and verify the positioning accuracy of the imaging systems.

Methods: Image quality was evaluated in terms of spatial resolution, low contrast resolution, image uniformity, and effective imaging area using a multi-purpose imaging phantom, Catphan 700 phantom, and ImageJ software. The influences of planning computed tomography (CT) slice thicknesses (1-5 mm), radiation quality settings (90-130 kV), and registration algorithms (bony, grayscale, and fiducial marker registrations) on positioning accuracy were assessed using anthropomorphic head-neck and thoracoabdominal phantom images. The clinical feasibility of both systems was validated in 22 enrolled patients.

Results: The CBCT exhibited a lower in-plane spatial resolution (2.50 line pairs per millimeter (lp/mm)) than DR (2.80 lp/mm). Spatial resolution of the CBCT system was measured at 0.90 lp/mm using the CTP 714 module of the Catphan 700 phantom. Both systems achieved a low contrast resolution of 2.30%. DR provided superior image uniformity (1.12%-1.40%) compared with CBCT (2.20%). The effective imaging areas were comparable between the CBCT and DR systems (99.30%-99.50%). Positioning accuracy varied with planning CT slice thicknesses, radiation quality settings, and registration algorithms, showing mean translation displacements ranging from 0.01 to 0.48 mm. CBCT achieved inter-fraction translational positioning errors within 2 mm in 42.3% (22/52) of fractions and rotational positioning errors within 2° in 80.8% (42/52) of fractions, and DR achieved 33.8% (24/71) and 73.2% (52/71), respectively.

Conclusion: The developed CBCT and DR systems achieved superior image quality and sub-0.5 mm positioning accuracy. These findings support the clinical feasibility of integrating CBCT and DR imaging systems into the C-ion RT workflow.

Background: The feasibility of total body irradiation (TBI) delivery using the TomoDirect mode of a TomoTherapy system has been demonstrated. In clinical practice, TomoTherapy-based TBI is typically performed in two parts: upper and lower body.

Purpose: This study aimed to evaluate the dosimetric impact of varying port numbers on dose evaluation indices for lower body irradiation using TomoDirect and to compare these results with those of TomoHelical in a simulation setting.

Methods: Sixteen patients who underwent myeloablative TBI using TomoHelical between October 2017 and March 2021 were retrospectively analyzed. TomoDirect plans with 2 to 12 ports at approximately equal beam angles were generated (modulation factor = 1.5, field width = 5.0 cm, pitch = 0.500). TomoHelical plans used identical parameters except for a pitch of 0.397. The prescribed dose was 12 Gy in six fractions. Dose indices (D2, D98, D50, homogeneity index [HI]) and beam-on time were compared.

Results: In TomoDirect plans, all dose evaluation indices worsened as the number of ports increased up to five, but changes became minimal beyond eight ports. D2 was significantly improved in all TomoDirect plans compared with those of TomoHelical plan. D98 was significantly lower for the three- and five-port TomoDirect plans, and no TomoDirect plan achieved higher D98 than TomoHelical. The D50 and HI were significantly improved in all TomoDirect plans except the five-port configuration. The two-port TomoDirect plan achieved the most favorable dose indices and the shortest beam-on time.

Conclusions: The two-port TomoDirect approach with anterior-posterior beam configuration provides an efficient and clinically reasonable option for lower-body irradiation, offering improved dose homogeneity and reduced treatment time compared with TomoHelical.

Purpose: Magnetic resonance imaging (MRI) and its importance in modern radiation therapy requires a standardized daily quality assurance (QA) procedure that is both comprehensive and efficient. Current imaging QA guidelines require a more inclusive analysis of imaging characteristics, as well as a simplification of setup procedures. We have studied the feasibility of using the Insight Phantom to provide consistent images for analyses of uniformity, slice thickness, spatial resolution, and distortion across a large field of view (FOV).

Methods: The large imaging region of the Insight Phantom was imaged using 3D True Fast Imaging with Steady State Precession (TruFi) and analyzed using the Modus QA software. The base and upright section were imaged in coronal, axial, and sagittal orientations over 3 months.

Results: Geometric distortion analysis yielded average maximum distortions within a 210 mm diameter of 0.57, 0.73, and 0.45 mm for axial, sagittal, and coronal orientations, respectively. Similarly, within a 310 mm diameter, average maximum distortions were 0.58, 0.73, and 0.74 mm with no distortions greater than or equal to 1 mm. Average modulation transfer function (MTF) values were 0.431 ± 0.007, 0.436 ± 0.007, and 0.433 ± 0.010 lp/mm for axial, sagittal, and coronal images, respectively. Finally, slice thickness values were consistent at 2.19 ± 0.04, 2.22 ± 0.06, and 2.24 ± 0.07 mm for axial, sagittal, and coronal imaging orientations, respectively. Images were repeatable and setup procedures were quick and straightforward, enhancing therapist workflow and efficiency.

Conclusion: The Insight Phantom's large coverage allows a more in-depth analysis of the MRI's large FOV, and its simple setup ensures a repeatable daily QA procedure for therapists. The software also provides a comprehensive analysis of key imaging parameters in a detailed report that can be used to monitor MRI functionality and quality.

Purpose: This study quantifies isocenter and off-axis geometric uncertainties using MultiMet Winston-Lutz (WL) tests to optimize gross tumour volume (GTV)-to-PTV (planning target volume) margin for single isocenter multiple target (SIMT) stereotactic body radiotherapy (SBRT) across three linear accelerators.

Methods and materials: Geometric inaccuracies were quantified for Trilogy (HD-MLC, 6 MV SRS), TrueBeam (Millennium MLC), and TrueBeam STx (HD-MLC, 6-degrees-of-freedom (6DoF) couch) using a Sun Nuclear MultiMet-WL cube containing six tungsten carbide markers arranged along the superior-inferior axis. The electronic portal imaging device (EPID) images acquired at four cardinal gantry angles with varied collimator/couch rotations were analyzed using MultiMet-WL software (v2.1) to measure 3D (Δ) displacements for all the LINACs. The required GTV-to-PTV margins were calculated using a modified van Herk formula (2.5Σ+1.64σ), incorporating measured 3D displacements for isocenter and off-axis targets.

Results: The TrueBeam STx (HD-MLC/6DoF) demonstrated superior geometric accuracy, maintaining ≤0.5 mm isocenter precision and ≤0.59 mm off-axis targeting (3-7 cm). The Trilogy exceeded TG-142 tolerances (1.06 ± 0.59 to 1.09 ± 0.57 mm) at all targets, requiring 4 mm uniform margins, while the TrueBeam (MMLC) showed optimal variations (isocenter: 0.68 ± 0.34 mm; superior off-axis: 0.74 ± 0.36 mm). Both TrueBeam platforms achieved sub-millimeter accuracy but demonstrated direction dependency for off-axis targets, requiring 2-3 mm anisotropic margins. Notably, isotropic margins introduced up to 11% delineation errors for off-axis targets due to these machine-specific geometric variations, highlighting the imperative for platform-specific margin protocols in SIMT SBRT.

Conclusion: This study demonstrates that routine analysis of MultiMet WL testing is an essential tool for the spatial accuracy of the LINAC to establish machine-specific PTV margin expansion in SIMT-SBRT, particularly for targets where rotational errors dominate.