Journal of Medical Physics最新文献

Objective: For stereotactic machines, recommendations demand stringent localization and precise delivery, as reflected by isocenter verification. Determining and analyzing the radiation isocenter for all clinical combinations of gantry, collimator, and couch are crucial for the quality of radiation therapy delivered. Although several radiation isocenter verification devices exist, there is no time-efficient system available for verifying the combined radiation isocenter. This paper presents a newly patented approach for the combined accuracy verification of the gantry, collimator, and couch radiation isocenter.

Methods: The novel combined radiation isocenter verification tool is used to expose a star test pattern on the dosimetric film at various angular combinations of the gantry, collimator, and couch. The exposed dosimetric film was evaluated using Radiochromic.com's standard third-party film analysis software.

Results: According to the results, the combined radiation isocenter for unit 1 is 0.74 mm dia (0.37 mm radius), and for unit 2, it is 0.62 mm dia (0.31 mm radius). These results are in good agreement with the requirements for three-dimensional conformal radiotherapy, intensity-modulated radiation therapy, volumetric-modulated arc therapy, stereotactic radiosurgery, and stereotactic body radiotherapy techniques.

Conclusion: This combined radiation isocenter verification tool aids in comprehensive evaluation of gantry, couch and collimator isocenters using radiographic film. It is easier to implement and faster to analyse compared to existing techniques, using a PC-based program that minimizes human error and increases measurement accuracy. This new approach can be used for routine quality assurance checks.

Background: Identifying plans at risk of patient-specific quality assurance (PSQA) failure through complexity metrics can reduce the workload while maintaining quality. This study evaluates complexity metrics as predictors of PSQA outcomes.

Materials and methods: A retrospective analysis was conducted on 192 IMRT plans for head-and-neck cancer. Complexity metrics were calculated using an in-house Python program. PSQA was performed with 3%/2-mm gamma passing rate (GPR) criteria, with plans classified as "Pass" (GPR ≥95%) or "Fail." Statistical analyses, including Spearman's correlation and receiver operating characteristic analysis, assessed the metrics' predictive value.

Results: Passing plans had an average GPR of 98.64 ± 1.33%, compared to 92.17 ± 2.35% for failing plans. The mean small area segment (MSAS) 5mm metric, with a threshold of 0.085, achieved a true positive rate of 38.17% and a false positive rate of 3.1%. Beam modulation and beam area indices also significantly differed between passing and failing plans.

Conclusion: MSAS5 and edge metrics showed strong potential for identifying high-risk plans. These metrics can guide targeted PSQA, improving workflow efficiency without compromising treatment safety.

Aims: The study aims to develop a modified Pix2Pix convolutional neural network framework to enhance the quality of cone-beam computed tomography (CBCT) images. It also seeks to reduce the Hounsfield unit (HU) variations, making CBCT images closely resemble the internal anatomy as depicted in computed tomography (CT) images.

Materials and methods: We used datasets from 50 patients who underwent Gamma Knife treatment to develop a deep learning model that translates CBCT images into high-quality synthetic CT (sCT) images. Paired CBCT and ground truth CT images from 40 patients were used for training and 10 for testing on 7484 slices of 512 × 512 pixels with the Pix2Pix model. The sCT images were evaluated against ground truth CT scans using image quality assessment metrics, including the structural similarity index (SSIM), mean absolute error (MAE), root mean square error (RMSE), peak signal-to-noise ratio (PSNR), normalized cross-correlation, and dice similarity coefficient.

Results: The results demonstrate significant improvements in image quality when comparing sCT images to CBCT, with SSIM increasing from 0.85 ± 0.05 to 0.95 ± 0.03 and MAE dropping from 77.37 ± 20.05 to 18.81 ± 7.22 (p < 0.0001 for both). PSNR and RMSE also improved, from 26.50 ± 1.72 to 30.76 ± 2.23 and 228.52 ± 53.76 to 82.30 ± 23.81, respectively (p < 0.0001).

Conclusion: The sCT images show reduced noise and artifacts, closely matching CT in HU values, and demonstrate a high degree of similarity to CT images, highlighting the potential of deep learning to significantly improve CBCT image quality for radiosurgery applications.

Objective: This study aimed to assess the irradiation techniques-three-dimensional conformal radiotherapy (3DCRT), RapidArc (RArc), and hybrid RapidArc (h-RArc)-for left-sided breast cancer patients, focusing on dose distribution in the planning target volume (PTV) and organs at risks (OARs).

Materials and methods: This study enrolled 20 patients diagnosed with early-stage left-sided breast cancer. All patients received a prescribed dose of 40.05 Gy in 15 fractions (2.67 Gy per fraction), optimized to achieve 95% dose coverage to 95% of the PTV. The dosimetric variations across the three treatment plans for the 20 patients were examined using a one-way ANOVA test. P <0.05 was regarded as statistically significant.

Results: In the 3DRCT plan, D95% of the PTV was 37.21 ± 0.51 Gy. This value was significantly increased to 39.43 ± 0.27 Gy in the RArc plan (P = 0.001) and to 38.47 ± 0.19 Gy in the h-RArc plan (P = 0.630). The RArc plans demonstrated a superior homogeneity index of 0.12 ± 0.02 compared to both 3DCRT (0.18 ± 0.02) and h-RArc (0.13 ± 0.02). When comparing the increase in monitor units (MUs), h-RArc showed a 62.82% increase over 3D-CRT, whereas demonstrating a 38.05% decrease compared to RArc (P = 0.000).

Conclusions: h-RArc treatment plans for breast cancer may be recommended due to their superior and consistent PTV dose coverage and sparing of OARs, in comparison to both 3DRCT and RArc plans. These h-RArc plans are characterized by reduced MU and beam on time, as well as a less low volume dose when compared to RArc plans.

Purpose: The purpose of this study was to report the commissioning the secondary dose calculation software ThinkQA (TQA) for an magnetic resonance-guided linear accelerator (MR-linac).

Methods: The Medical Physics Practice Guideline 5.a. (MPPG5a) tests, and dose in inhomogeneities, beam profiles, and depth dose curves were calculated and compared between Monaco and TQA. Five intensity modulated radiotherapy (IMRT) plans (anal, abdominal, head and neck, prostate, and lung), based on TG-244 guidelines were evaluated varying the gamma criteria. Furthermore, the initial and adapted plans for the first session for 17 patients in different anatomical regions were calculated in TQA using different gamma criteria. For five patients, six measurements were made at different fractions using ArcCheck and compared with TQA.

Results: The majority of tests met the tolerances defined in the MPPG5a with the exception of dose profiles (>10%), and large multileaf collimator-shaped fields with extensive blocking (>2%). For the IMRT plans, tight criteria such as 2%/2 mm may not be suitable for all scenarios. Thus, we adopt a reasonable 3%/2 mm without compromising the quality of the plan that included significant high-to-low-density interfaces. It is observed that, the values obtained for clinical cases are in the range from 94.6% to 99.8% (TQA), 97.0% to 99.6% (ArcCheck), except in a prostate case with 87.8% (TQA) and 99.3% (ArcCheck).

Conclusion: We commissioned TQA as a secondary dose calculation for MR-linac and we introduced it clinically for adaptive treatment workflow using 3%/2 mm with 95% as tolerance limit and 90% as action limit.

Aim: The study aims to compare the accuracy of Anisotropic Analytical Algorithm (AAA) and acuros XB (AXB) dose calculation algorithms for radiotherapy (RT) planning of rectal tumors.

Materials and methods: Treatment plans from 20 patients with previously treated rectal cancer were retrospectively analyzed. All patients underwent VMAT treatment planning using the AAA algorithm in Eclipse (v15.6) system. These plans were recalculated with AXB in Eclipse (v15.6) while maintaining the original multileaf collimator fluence. Dosimetric parameters and gamma analysis (3%/3 mm and 2%/2 mm criteria) were compared between the two algorithms. A paired two-tailed t-test was used to statistically compare dosimetric and gamma analysis results between the AAA and AXB algorithms.

Results: The results indicate that AAA could be potentially overestimating the dose to planning target volume (PTV). While the mean bowel dose was marginally lower in AAA plans (P = 0.013), doses to other organs at risk (OARs) were slightly higher, suggesting a general overestimation trend. This implies that AAA could be potentially overestimating the dose to OARs and PTV as compared to AXB. The statistical analysis of the Gamma parameters also shows a significant change.

Conclusion: The results indicate that the dose calculation accuracy of AXB is superior to AAA for rectal cancer RT.

The radiation dosimetry used to measure the ionizing radiation dose delivered during X-ray imaging procedures in planar radiography units, especially in fluoroscopy, is the dose-area product (DAP). DAP is used as the primary parameter for recording diagnostic reference levels, which are guidance values for optimizing patient radiation dose. DAP is reported by the system's DAP meter, which needs to be calibrated appropriately. This study evaluates the influence of dosimeters and field markers on the accuracy of DAP levels in the DAP meter in situ calibration method. The aim of this study is to recommend a combination of dosimeter types and field markers with the highest accuracy for the beam-area method. Two methods of DAP meter in situ calibration were compared: the tandem method with a reference DAP meter as the reference DAP value and the beam-area method using ion chamber dosimeters, solid-state dosimeters, as well as field markers from digital radiography (DR) and computed radiography. This method was applied to the DAP meter in the Allura XPER FD 20 angiography (Philips, Amsterdam, the Netherlands) unit. The results showed that the combination of ion chamber dosimeter and DR field markers at a distance of 55 cm produced the most accurate DAP values (lowest root mean square error value, 0.10). The recommended calibration method can be used to confirm the actual DAP value in X-ray imaging in a planar radiography unit.

Purpose: This study evaluated whether the mini-ridge filter (MRF) used for beam energy optimization in a synchrotron-based proton beam therapy (PBT) affects the generation of secondary neutrons and photons.

Materials and methods: Secondary radiation from the PBT was evaluated using a Monte Carlo simulation (MCS) with the Particle and Heavy-ion Transport code System (version 3.31), and the PROBEAT-M1 system (Hitachi, Japan) was modeled. In the analysis, we focused on the production of neutrons and photons in a 35 cm ×35 cm ×35 cm water phantom with and without MRF to ensure the accuracy of the dose calculation.

Results: The MCS results were in good agreement with the measurement results, and the off-axis ratio at the center of the spread-out Bragg peak was 100% at a gamma analysis pass rate of 2 mm/2%. The photon fluence decreased by 4.0 and 0.9% at 70.2 and 228.7 MeV, respectively, but no significant effect on total neutron and photon production was observed (P > 0.05). The MRF effect on the dose was <0.11 μGy Gy^-1, suggesting that a clinically significant effect is negligible.

Conclusions: These results demonstrated that MRF had a limited effect on the generation of secondary radiation in PBT. MRF, which is used to improve dose distribution, has the potential to be safely used without increasing secondary radiation, and MRF might not affected to generate secondary radiation to clinically meaningful levels.

The comparative effectiveness of traditional lead aprons versus newer generation lead-free alternatives in radiation protection is a critical area of investigation in medical safety. While lead aprons have long been the standard, concerns over weight and mobility have spurred interest in lead-free options, which incorporate materials such as antimony, bismuth, and barium sulfate. Understanding the relative performance of these apron types is essential for optimizing radiation protection protocols in medical settings. Relevant studies were identified through electronic database searches, with inclusion criteria focusing on comparative evaluations of apron types in terms of radiation shielding effectiveness and durability. Data extraction and risk of bias were performed to analyze key findings across the selected studies. Analysis of the included eleven studies revealed promising results for lead-free aprons, demonstrating comparable radiation protection to traditional lead aprons. In addition, thinner lead-free aprons were proven to be adequate for shielding while concerns related to weight and mobility. The systematic review highlights the evolving landscape of radiation protection in medical settings, with newer-generation lead-free aprons presenting promising alternatives to traditional lead aprons. In addition, shields composed of combined metals demonstrated more substantial attenuation and dose reduction in comparison to single-metal shields.