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: RapidArc Dynamic (RAD) integrates static-angle modulated ports (STAMPs) and a dynamic collimator into arc delivery. The optimal use of RAD, including the ideal number of STAMPs, the best use of the dynamic collimator, and the ideal relative weighting between arc and STAMPs, has yet to be reported. We aim to investigate optimized utility of these parameters for breast and chest wall treatment planning to achieve superior dosimetric results.

Methods: Thirteen breast and chest wall patients were planned using RAD. Plans were created using the three different dynamic collimator options, five different arc/STAMP weighting options, and with 2, 4, and 6 STAMPs. All plans were created with automated skin flash. RAD plans were compared to conventional RapidArc (RA) plans. The DVH metrics and MUs for each plan were recorded, and a paired T-test was used to test for statistically significant (p ≤ 0.05) differences between the plans.

Results: "Optimize between static angles" was the best option for dynamic collimator setting. Increasing the number of STAMPs from 2 to 4 or 6 lowered PTV V105% in patients where the PTV V105% was high but provided limited benefit in most patients. Selecting arc-dominant weighting yields significantly worse DVH metrics than a balanced weighting. Dosimetric differences were minimal between (0) Balanced, (1) Static, or (2) Static-Dominant weighting.

Conclusions: The following are recommended as a starting point for breast and chest wall RAD plans: 2 STAMPs positioned similar to breast tangents, "optimize between static angles" for the dynamic collimator, and a weighting of either (0) balanced, (1) static, or (2) static-dominant. The arc-dominant setting resulted in plans of the lowest quality.

Background: Intraoperative cone-beam computed tomography (CBCT) provides a valuable option for accurate three-dimensional applicator positioning in gynecologic brachytherapy, but is associated with radiation exposure and increased intervention time especially in case of repeated CBCT imaging being required for creating a sufficient implant arrangement.

Purpose: To reduce the need for multiple CBCT scans for corresponding applicator verification, this work proposes two methods for needle path navigation, including corrections of potential bending in situ, by combining infrared tracking with planar x-ray imaging for enabling accurate intraoperative needle guidance.

Methods: An examined 200 mm brachytherapy needle was rigidly mounted on an infrared-reflective tracking tool to enable real time tracking. Two planar x-ray images, acquired from varying distinct angles, were used to determine the exact 3D position of the needle tip region via backprojection. A spline was fitted through the obtained coordinates to reconstruct the full needle path. Based on this, only a single initial CBCT scan was required to visualize the predicted needle path within this scan. Additionally, a second approach for needle prediction was presented focusing on only one planar x-ray image by incorporating prior needle bending information from the initial CBCT scan. Both methods were evaluated in preclinical studies and validated against a corresponding ground-truth obtained from CBCT.

Results: The proposed method considering two planar x-ray images successfully reconstructed the needle path with deviations of less than 1 mm from the CBCT reference scan, when using at least 20° offset between the x-ray image acquisitions. The single-scan approach, using prior bending information, yielded promising results with deviations at the tip of below 1.3 mm.

Conclusions: Both described methods demonstrated their feasibility in preclinical studies, showing potential to improve and accelerate clinical implantation workflows by means of needle navigation in the future.

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: 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: Following the release in 2016 of the report of the American Association of Physicists in Medicine Task Group 100, there has been growing interest in the use of prospective hazard analysis in radiation therapy. System Theoretic Process Analysis (STPA) is an emerging technique in this domain that is particularly suited to processes that involve time sensitive collaboration, decision-making and/or automation.

Purpose: The goal of this research was to use STPA to evaluate existing processes and procedures with an aim to identify improvements, gaps or unforeseen risks stemming from implementing real-time adaptive treatment on a helical tomotherapy platform.

Methods: The Radixact treatment delivery system (Accuray Inc., Sunnyvale, CA, USA), an evolution of the Tomotherapy platform, incorporates upgrades such as the Synchrony system for real-time motion monitoring and treatment adaptation. In collaboration with a team from the radiation oncology department of a large public hospital, a prospective hazard analysis focused on the real-time adaptive capabilities of the Radixact Synchrony system was conducted using STPA. The system boundaries were defined and a control structure model comprising sub-systems and control actions was developed. Unsafe control actions were identified and broad-based causal scenarios were generated. The causal scenarios that were novel, specific to Synchrony or challenging to mitigate were selected for further analysis regarding impacts and potential causes, following which mitigation strategies were proposed, taking into consideration the hierarchy of controls.

Results: A control structure model encompassing the entire patient journey was developed, incorporating all the hardware and software components and human decision makers. The model consisted of 12 sub-systems and 21 control actions, resulting in 108 unsafe control actions and 595 causal scenarios. Sixty-one causal scenarios were selected for further analysis, for which mitigation strategies were proposed based on the hierarchy of controls. These included the development of better reference documentation, the systematic testing of the sensitivity of tracking performance to changes in tracking parameters, guidance around setting and documenting tracking parameters, and documentation review.

Conclusions: STPA was effectively used to assess the Radixact Synchrony system's real-time adaptive radiation therapy capabilities, providing insight into how the system could become unsafe throughout the patient journey. While focused on Radixact Synchrony and real-time adaptive radiation therapy, this study offers a transferable example of STPA application, from analysis initialization to mitigation, that can inform other safety assessments in radiation therapy.

Background: Using a constant relative biological effectiveness (RBE = 1.1) in proton therapy may underestimate the RBE-weighted dose in high linear energy transfer (LET) regions at the distal end of the beam, thereby limiting the ability to accurately predict clinical outcomes.

Purpose: To commission and validate a Monte Carlo (MC) model incorporating variable RBE for breast cancer proton therapy, enabling improved RBE-weighted dose calculation.

Methods: A FLUKA-based MC model of a raster scanning proton beamline was commissioned and benchmarked against the clinically employed treatment planning system (TPS) (Siemens Syngo) and physical measurements. Dose-averaged LET (LET_d) and variable RBE-weighted dose distributions were computed using McMahon (McM), McNamara (McN), and Wedenberg (Wed) models. Treatment plans for four representative breast cancer cases were recalculated to compare TPS and MC results using dose-volume histograms (DVH) and three-dimensional gamma (γ) analysis. LET_d-volume histograms (LVH) and variable RBE-weighted dose distributions were analyzed to compare cases without adverse effects versus those presenting rib fractures or radiation pneumonitis.

Results: The FLUKA-MC model showed good agreement with both the TPS results and the measured data, exhibiting proton range deviations within ±0.1 mm. The γ pass rates for the four patients are 94.0%, 92.2%, 92.6%, and 86.7%, respectively. LET_d analysis of 0.5 cm³ volumes of rib revealed numerical differences (fracture cases: 11.1 and 10.8 keV/µm; non-fracture: 9.2 and 10.0 keV/µm). The RBE-weighted dose to 0.5 cm³ of the ribs was consistently elevated in fracture cases across all models (RBE = 1.1: 46.2-49.0 Gy; McM: 54.6-56.5 Gy; McN: 51.0-53.3 Gy; Wed: 50.6-52.5 Gy) versus non-fracture cases (RBE = 1.1: 44.0-45.3 Gy; McM: 52.2-53.8 Gy; McN: 48.6-50.1 Gy; Wed: 48.3-49.8 Gy). The estimated RBE values in the rib region were 1.60 (McM), 1.38 (McN), and 1.44 (Wed), which were derived from the mean LET_d within 0.5 cm³ rib volumes. The RBE-weighted lung V20 was elevated in pneumonitis patients across all models. All variable RBE models predicted elevated RBE-weighted doses in distal proton beam regions across cases.

Conclusions: The commissioned MC framework demonstrated the feasibility of integrating multiple variable RBE models for RBE-weighted dose estimation in proton therapy.