Journal of Medical Physics最新文献

Background: Management of brain arteriovenous malformations (bAVMs) close to motor areas with stereotactic radiosurgery (SRS) is challenging due to the risk of radiation-related morbidity. This risk stems from the increased radiosensitivity of the surrounding white matter (WM), which is crucial for preserving motor function.

Purpose: This study aimed to investigate the application of diffusion tensor imaging (DTI)-based magnetic resonance (MR) tractography SRS planning for bAVMs, with a focus on sparing WM tracts during CyberKnife treatment. The goal was to minimize radiation exposure to motor-relevant WM tracts, thereby reducing the risk of posttreatment motor deficits and improving patient outcomes.

Materials and methods: The DTI-based reconstructions of WM tracts from 22 patients with motor-eloquent bAVMs were integrated into the CyberKnife planning system and co-registered with treatment planning images. The WM tracts, located within normal tissue and not overlapping with the target volume of the bAVMs, were delineated as dose constrain volumes. Initial treatment plans, excluding WM tracts, were compared with WM tracts constraint plans that incorporated these tracts to assess and compare radiation doses delivered to WM structures in both plans.

Results: With WM tracts constraint, maximum dose of WM tracts can be reduced by 17.68% on average (range 13.61%-33.29%), thus from 20.81 Gy to 17.13 Gy (P < 0.01). The dose-volume histogram analyses have shown that a significant reduction was achieved for WM tracts (V50% P < 0.01, V40% P < 0.01, V30% P < 0.001, and V20% P < 0.05). There was no significant impact on planning target volume coverage (96.26 ± 0.68 vs. 96.13 ± 0.47, P = 0.587) and all dose constraints for organs at risks and other planning parameters were fully satisfied.

Conclusion: Integrating DTI-based MR tractography into CyberKnife SRS for motor-eloquent bAVMs was feasible and preserves critical motor tracts without compromising radiation therapy goals.

Objective: The objective of this work is to measure the imaging dose in two-dimensional kilovoltage (kV) image guided radiotherapy using in-house developed free air ionization chamber (FAIC).

Materials and methods: In-house developed FAIC and a commercially available shadow-free diagnostic (SFD) detector were used in this work. Reference points of the dosimeters were positioned at 100 cm distance from the focal spot of the x-ray tube of an on-board imager. The blades of x-ray tube were opened to 26.6 cm × 20 cm. The FAIC was operated at 3800 V supplied by an indigenously developed external high-voltage power supply, whereas the SFD was operated at 300 V supplied by the electrometer. The dosimeters were irradiated using head (70 kV, 9.77 mAs), abdomen (100 kV, 25.39 mAs), pelvis (110 kV, 29.30 mAs), and extremity (65 kV, 6.84 mAs) protocols. The air kerma per unit mAs was determined using the collected charge and the values determined in this work were compared with the values reported in the literature.

Results: The measured air kerma by FAIC and SFD were in good agreement with each other within the uncertainty of measurement. However, the FAIC and SFD measured values were approximately 42% lesser than the values of air kerma reported in the literature.

Conclusions: The default imaging protocols are optimized for image quality and patient dose, further optimization of exposure parameters according to the patient anatomy may help in reducing the imaging dose further.

Purpose: This study aimed to explore the construction method of a RapidPlan (RP) model for cervical cancer based on knowledge-based planning (KBP) and to evaluate the effect of its combined application with multicriteria optimization (MCO) technology.

Methods: Eighty cervical cancer patients treated with postoperative radiotherapy in our hospital were retrospectively selected and then randomly divided into two groups: 60 patients for model training and 20 patients for testing. Using professional algorithms and software tools, we constructed an RP model. This model was then combined with MCO technology to design and optimize treatment plans for cervical cancer cases, generating a combined RP_MCO plan. We statistically compared and analyzed the differences in planning efficiency and dosimetric parameters, such as target coverage and doses to organs at risk (OARs), between the combined plan and traditional manual plans (MPs).

Results: The RP_MCO group significantly reduced the planning time compared to the MP group and the MP_MCO group. Specifically, the RP_MCO group decreased the planning time by 15.2 min compared to the MP group (P < 0.001). In terms of target dose, compared to MP, RP_MCO improved RP_MCO improved target coverage, increasing the minimum dose by 0.58 Gy (P < 0.05), reducing the maximum dose by 0.72 Gy (P < 0.01), and enhancing GI by 0.57 (P < 0.001). The RP_MCO group showed better OAR protection than the MP and MP_MCO groups and also had advantages over the RP group in some OAR protection.

Conclusion: The combination of the KBP-based RP model and MCO provides a more efficient and higher-quality planning design scheme for cervical cancer radiotherapy. This approach is expected to enhance treatment outcomes and promote the quality of life for cervical cancer patients in clinical practice.

Introduction: Ionizing radiation causes deoxyribonucleic acid (DNA) damage through both direct and indirect mechanisms. This study aimed to investigate and quantify the biological response of ion beams in biological matter and the radiation-induced DNA damage using Monte Carlo (MC) simulations. The study provides insights into the potential benefits of novel helium ion beams in charged-particle cancer therapy.

Materials and methods: The Geant4-DNA MC toolkit was used to study the biological response to radiation and the resulting DNA damage. The MCF-7 breast adenocarcinoma cancer cell line was simulated. Helium ion beams with varying linear energy transfer values were irradiated onto the cancer cell line.

Results: The radiobiological endpoints, in terms of damage yield and the single-strand break (SSB)/double-strand break (DSB) ratio, for the MCF-7 cancer cell line were retrieved and compared with published simulation-based studies and experimental studies. The damage yield and SSB/DSB ratio in this study were in good agreement with published simulation-based studies. However, the DSB yield in this study was higher than the experimental results from published studies.

Conclusion: This study demonstrated the capabilities of the Geant4-DNA MC techniques in providing a mechanistic understanding of radiation-induced DNA damage in human cancer cell lines and quantifying the resulting DNA damage.

Purpose: Cone-beam computed tomography (CBCT) is widely used in imaging-guided radiotherapy for precise treatment planning and patient positioning. However, the ionizing radiation used in CBCT poses inherent risks to patients.

Materials and methods: This study evaluated the feasibility of radiophotoluminescent. glass dosimeter system GD-352M for measuring radiation dose in kilovoltage CBCT (kV-CBCT).

Results: The GD-352M demonstrated good uniformity, linearity, accuracy, reproducibility, and low-energy dependence. Moreover, the FDG-1000 automatic reader system exhibited consistent readout values that were not influenced by the magazine's position. The GD-352M demonstrated good uniformity, linearity, and accuracy, with a combined measurement uncertainty of 4.56%, confirming its suitability for kV-CBCT dosimetry.

Conclusion: These findings indicate the suitability of the GD-352M dosimeter for measuring dose range in kV-CBCT and improve patient safety in kV-CBCT dosimetry.

Purpose: Patient-specific quality assurance (QA) for CyberKnife is typically performed using micro ionization chambers and film dosimetry. However, micro ionization chambers tend to underestimate dose measurements in small radiation fields. Therefore, scintillation detectors, with their small detector size, may be more suitable for point dosimetry in CyberKnife QA. The purpose of this study was to evaluate the utility of a scintillation detector (Exradin W2 [W2]) for point dose measurements in CyberKnife patient-specific QA.

Methods: Dosimetric measurements for 50 treatment plans involving intracranial stereotactic radiotherapy were performed using both the W2 and a micro ionization chamber (Exradin A16 [A16]).

Results: The mean point dose differences in patient-specific QA were 0.5% for W2 and -6.6% for A16; dose differences with W2 were generally within ±3%. Factors contributing to measurement robustness included the optical fiber dose for W2, and the static cable dose and collimator size for A16.

Purpose: Knowing the downtime of linear accelerators (LINACs), as well as the intermediate time between failures, is essential to plan and carry out timely and reliable radiotherapy treatments. The purpose of this study is to analyze the data in the service reports of LINACs installed in four radiotherapy centers, by calculating indicators and metrics of their maintenance, as well as studying factors linked to their downtime, such as the spare parts used in the repairs of the equipment.

Methodology: The maintenance database of LINAC of the commercial house Varian Medical Systems, was analyzed, and distributed in 5 years of a Clinac iX and a Clinac 2100CD, 4 years of a Clinac 21EX and a Clinac 2100CD, and 3 years of a Clinac 600C, located in different medical centers of oncological radiotherapy in the country. The data were classified according to the equipment, interlock, and area of failure in the equipment.

Results: On average, 20 corrective maintenance tasks were performed annually for each equipment, and 33.9% of the corrective maintenance tasks performed were caused by the multileaf collimator (MLC) interlock. Of the three possible types of interlocks (major, minor, and dosimetry), 83% of the time, a minor type of interlock occurs. Regarding the location of the faults, 32% occur in the MLC. In addition, it was determined that the most requested spare part is the "Half Leaf MLC Motor."

Conclusion: Collecting data associated with the downtime of LINACs and using them to calculate the indicators and metrics proposed in this research will allow for monitoring and implementing improvements in the planning of maintenance and treatments. Likewise, studying the demand for spare parts necessary to perform maintenance ensures proper inventory management.

Aims: This study aimed to confirm the accuracy of the dose calculation by commercially available treatment planning system (TPS) at the extended SSD = 350 cm with and without beam spoiler configurations.

Materials and methods: Two extended SSD plans, one without a beam spoiler and another with a beam spoiler, were created on a virtual phantom in Eclipse TPSs for 6 MV photon beam. Using dosimetry tools, percentage depth doses (PDDs) and in-line profiles of both plans were generated. Beam properties of the TPS calculated PDDs and profiles were compared with manually calculated and measured PDDs and profiles. Reference depth dose was calculated in two different phantoms and measured using an ion chamber and TLDs.

Results: At the extended SSD setup, the TPS calculated and measured PDD with and without beam spoiler were in agreement within 2%. This agreement was observed at the surface and in the buildup region as well. Flatness and symmetry of the profiles with and without beam spoiler were within ± 3%. The TPS calculated dose at a reference depth in a homogeneous and a heterogeneous phantom was agreed with measured dose using an ion-chamber and TLDs.

Conclusion: This study validated the TPS for extended SSD total body irradiation (TBI) dose calculation with and without beam spoiler. Developing computed tomography based field in field plan for homogeneous dose distribution may be feasible. This technique may allow us to treat extended SSD TBI in less time while maintaining dose calculation accuracy.

Objective: This study aims to evaluate and compare the dosimetric performance of tandem ovoid (TO) and tandem ring (TR) applicators in image-guided high-dose-rate intracavitary brachytherapy for cervical cancer.

Materials and methods: Computed tomography datasets from 45 cervical cancer patients treated with either TO or TR applicators were analyzed. Dose-volume histograms were generated, and dose parameters for the target and organs at risk (OARs) were recorded for each insertion. Key dosimetric metrics, including doses to points A and B, D90 for the clinical target volume (CTV), and 2cc doses for the bladder, rectum, and sigmoid, were compared between the two applicator groups.

Results: Dosimetric outcomes for target volumes showed no significant differences between TO and TR applicators, with comparable doses to point A (P = 0.12), point B (P = 0.43), and D90 CTV (P = 0.10). Similarly, OAR doses for the bladder (P = 0.10), rectum (P = 0.15), and sigmoid (P = 0.10) were statistically equivalent. However, TR applicators consistently delivered significantly higher doses to vaginal dose points (except anterior 5 mm points), highlighting a notable difference in dose distribution patterns.

Conclusion: While both TO and TR applicators achieve similar dosimetric outcomes for the target and major OARs, the TR applicators are associated with significantly higher vaginal dose exposure. This distinction may have clinical implications, particularly for patients at risk of vaginal toxicity, and underscores the importance of applicator selection based on individual patient anatomy and treatment goals.

Introduction: Photon-counting computed tomography (CT) is equipped with an adaptive iterative reconstruction method called quantum iterative reconstruction (QIR), which allows the intensity to be changed during image reconstruction. It is known that the reconstruction conditions of CT images affect the analysis results when performing radiomic analysis. The aim of this study is to investigate the effect of QIR intensity on image quality and radiomic analysis of renal cell carcinoma (RCC).

Materials and methods: The QIR intensities were selected as off, 2 and 4. The image quality evaluation items considered were task-based transfer function (TTF), noise power spectrum (NPS), and low-contrast object specific contrast-to-noise ratio (CNR_LO). The influence on radiomic analysis was assessed using the discrimination accuracy of clear cell RCC.

Results: For image quality evaluation, TTF and NPS values were lower and CNR_LO values were higher with increasing QIR intensity; for radiomic analysis, sensitivity, specificity, and accuracy were higher with increasing QIR intensity. Principal component analysis and receiver operating characteristics analysis also showed higher values with increasing QIR intensity.

Conclusion: It was confirmed that the intensity of the QIR intensity affects both the image quality and the radiomic analysis.