Quality assurance of Cyberknife robotic stereotactic radiosurgery using an angularly independent silicon detector

Purpose: The aim of this work was to evaluate the use of an angularly independent silicon detector (edgeless diodes) developed for dosimetry in megavoltage radiotherapy for Cyberknife in a phantom and for patient quality assurance (QA). Method: The characterization of the edgeless diodes has been performed on Cyberknife with fixed and IRIS collimators. The edgeless diode probes were tested in terms of basic QA parameters such as measurements of tissue-phantom ratio (TPR), output factor and off-axis ratio. The measurements were performed in both water and water-equivalent phantoms. In addition, three patient-specific plans have been delivered to a lung phantom with and without motion and dose measurements have been performed to verify the ability of the diodes to work as patient-specific QA devices. The data obtained by the edgeless diodes have been compared to PTW 60016, SN edge, PinPoint ionization chamber, Gafchromic EBT3 film, and treatment planning system (TPS). Results: The TPR measurement performed by the edgeless diodes show agreement within 2.2% with data obtained with PTW 60016 diode for all the field sizes. Output factor agrees within 2.6% with that measured by SN EDGE diodes corrected for their field size dependence. The beam profiles\u27 measurements of edgeless diodes match SN EDGE diodes with a measured full width half maximum (FWHM) within 2.3% and penumbra widths within 0.148 mm. Patient-specific QA measurements demonstrate an agreement within 4.72% in comparison with TPS. Conclusion: The edgeless diodes have been proved to be an excellent candidate for machine and patient QA for Cyberknife reproducing commercial dosimetry device measurements without need of angular dependence corrections. However, further investigation is required to evaluate the effect of their dose rate dependence on complex brain cancer dose verification

Development and characterization of solid-state detectors for medical dosimetry in Intensity Modulated Radiation Therapy and Stereotactic Radiosurgery

In the last decade, the majority of radiotherapy treatments are delivered via advanced radiotherapy technologies such as intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT) and stereotactic body radiation therapy (SBRT). The unique properties of these modalities such as small and irregular field shapes, continuously varying fluence/dose rates, and beam delivered at several different angles and from non-coplanar directions produces non-uniform, modulated intensity and conformed absorbed dose distribution which in turn improves the outcome of the treatment. However, the complexities associated with these technologies can create large deviations in treatment dose, requiring extensive dose measurement verification and quality assurance (QA) procedures to ensure the patient’s treatment is performed correctly and safely

Improving Alzheimer’s Disease Classification in Brain MRI Images Using a Neural Network Model Enhanced with PCA and SWLDA

The examination of Alzheimer’s disease (AD) using adaptive machine learning algorithms has unveiled promising findings. However, achieving substantial credibility in medical contexts necessitates a combination of notable accuracy, minimal processing time, and universality across diverse populations. Therefore, we have formulated a hybrid methodology in this study to classify AD by employing a brain MRI image dataset. We incorporated an averaging filter during preprocessing in the initial stage to reduce extraneous details. Subsequently, a combined strategy was utilized, involving principal component analysis (PCA) in conjunction with stepwise linear discriminant analysis (SWLDA), followed by an artificial neural network (ANN). SWLDA employs a combination of forward and backward recursion methods to choose a restricted set of features. The forward recursion identifies the most interconnected features based on partial Z-test values. Conversely, the backward recursion method eliminates the least correlated features from the same feature space. After the extraction and selection of features, an optimized artificial neural network (ANN) was utilized to differentiate the various classes of AD. To demonstrate the significance of this hybrid approach, we utilized publicly available brain MRI datasets using a 10-fold cross-validation strategy. The proposed method excelled over existing state-of-the-art systems, attaining weighted average recognition rates of 99.35% and 96.66%, respectively, across all the datasets

Evaluation of the PTW microDiamond in edge-on orientation for dosimetry in small fields

© 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine Purpose: The PTW microDiamond has an enhanced spatial resolution when operated in an edge-on orientation but is not typically utilized in this orientation due to the specifications of the IAEA TRS-483 code of practice for small field dosimetry. In this work the suitability of an edge-on orientation and advantages over the recommended face-on orientation will be presented. Methods: The PTW microDiamond in both orientations was compared on a Varian TrueBeam linac for: machine output factor (OF), percentage depth dose (PDD), and beam profile measurements from 10 × 10 cm2 to a 0.5 × 0.5 cm2 field size for 6X and 6FFF beam energies in a water tank. A quantification of the stem effect was performed in edge-on orientation along with tissue to phantom ratio (TPR) measurements. An extensive angular dependence study for the two orientations was also undertaken within two custom PMMA plastic cylindrical phantoms. Results: The OF of the PTW microDiamond in both orientations agrees within 1% down to the 2 × 2 cm2 field size. The edge-on orientation overresponds in the build-up region but provides improved penumbra and has a maximum observed stem effect of 1%. In the edge-on orientation there is an angular independent response with a maximum of 2% variation down to a 2 × 2 cm2 field. The PTW microDiamond in edge-on orientation for TPR measurements agreed to the CC01 ionization chamber within 1% for all field sizes. Conclusions: The microDiamond was shown to be suitable for small field dosimetry when operated in edge-on orientation. When edge-on, a significantly reduced angular dependence is observed with no significant stem effect, making it a more versatile QA instrument for rotational delivery techniques

Characterization of an Edgeless Dosimeter for Angular Independent Measurements in Advanced Radiotherapy Treatments

In this paper, the performance of an edgeless device is evaluated for use as an angular independent detector for dosimetric quality assurance in radiotherapy. The edgeless diodes were tested in terms of current-voltage (IV) and capacitance- voltage (CV) characteristics, charge collection efficiency and radiation hardness. A model of the edgeless device was developed to simulate the distribution of the electric field for different geometries using technology computer aided design (TCAD). IV and CV characteristics of the diodes indicate the appropriate operational conditions and provide a means to assess the consistency/ quality of the edgeless diode technology. TCAD model shows good agreement with experimental results demonstrating the accuracy of the model in simulating the behavior of the edgeless diodes. The charge collection efficiency is evaluated for two of the edgeless configurations PP and NP. The angular dependence measurements of edgeless devices before and after 2 Mrad irradiation shows negligible effect of radiation damage on response as a function of the angle. The experimental data are supported by the results of the TCAD simulation study, which indicates negligible impact of radiation damage from a clinical use perspective. Both the experimental and simulated results derived from the radiation damage study show minimal degradation (within 4%) of the diodes sensitivity

Feasibility of a dual detector system to perform transit dosimetry and MV imaging in-vivo

In this work, a dual detector system for simultaneous in-vivo dosimetry and MV imaging was investigated. The ability to measure real-time water equivalent dose post transit for a heterogeneous phantom was demonstrated, illustrating its advantage over non-water equivalent EPID dosimetry. Identification of incorrect MU delivery as well as patient misalignment can be identified in the dose profiles and confirmed through co-registration with EPID images. The dual detector comprising of a silicon array detector Magic Plate (MP) and an EPID was positioned beneath the patient couch at a source to detector distance of 150 cm. Two pseudo lung phantoms were utilised in this study; identical, except for the inclusion of a water equivalent hidden target mimicking a tumour. The dosimetric accuracy of the MP was evaluated with EBT3 film and TPS calculations. The presence and position of the hidden target was detected and accurately co-registered between the dose profiles measured with MP and the EPID image. The system measured a difference in post transit doses through the two phantoms of (5.0 ±1.6) cGy due to the presence of the target, in agreement with the TPS calculation of 5.16 cGy. The capability of the system for error detection was confirmed when a deliberate 7 mm lateral shift of the phantom was observed in both the dose profiles measured with MP and the EPID images. The MP as a dosimetric real time detector is lucent in MV photon fields and does not obstruct the EPID field of view