Optical Computed Tomography Scanner Research Articles

Utilizing acrylic acid polymer hydrogel for 3-D quality assurance in CyberKnife radiotherapy

Dosimetry tools play a crucial role in radiotherapy as they are essential for recording and validating intricate 3-D dose distributions. This research introduces and examines a novel acrylic acid polymer hydrogel (ACAPHG) dosimeter composition designed for 3-D dose verification and quality assurance in the context of radiotherapy treatment. A phantom made of an 80 mm diameter cylindrical glass container was utilized. The phantom contained the hydrogel, which served as the medium for radiation exposure. The water equivalent hydrogel within the phantom was subjected to irradiation by a CyberKnife robotic radiotherapy system. An optical computed tomography (OCT) scanner with sub-millimeter resolution was used to obtain imaging data. The dose distribution of a CyberKnife robotic SRS/SBRT treatment plan for a brain cancer patient was compared to that of the hydrogel's OCT scan using 2-D and 3-D gamma analysis with a criterion of 3% dose difference and 3 mm distance-to-agreement. A gamma pass rate of 94.1% for the 2-D gamma analysis and a pass rate of 99% for the 3-D gamma analysis were calculated within the region at which the treatment planning system data drops to 20% of the maximum dose. The use of the ACAPHG dosimeter in conjunction with the described setup suggests that it has the potential to offer an accurate 3-D verification of complex dose distributions in SRS/SBRT radiotherapy treatments. By employing the ACAPHG dosimeter and utilizing OCT scanning, this dosimeter enables the assessment and validation of intricate dose distributions in these advanced radiotherapy treatments.

Two-dimensional sound pressure distribution: Visualization and calibration-free quantification via optical wave microphone CT scanning

In recent years, the optical wave microphone has emerged as an innovative technique, employing Fraunhofer diffraction of a laser beam, and shows promising applications in various acoustic domains where high electric and/or magnetic fields preclude the use of traditional microphones. This study utilized an optical wave microphone computed tomography (CT) scan and calibration-free quantification to ascertain sound pressure levels at multiple distances from the ultrasonic oscillator. The cornerstone of this study, which is different from the author’s previous studies, is the quantification of sound pressure distribution via a theoretical model that encompasses all physical parameters pertinent to the optical wave microphone’s experimental arrangement. This method has proven effective in visualizing and quantifying the two-dimensional sound pressure distribution emitted by an ultrasonic oscillator (40 kHz) without the necessity for calibration. The results demonstrate that the sound pressure distribution determined using the calibration-free optical wave microphone CT scan is in good agreement with the measurements obtained through a condenser microphone.

Patient-specific quality assurance in SBRT treatments using 3D polymer gel dosimetry

In stereotactic body radiation therapy (SBRT), patient-specific quality assurance (PSQA) is required due to the complex dose distributions delivered. In this context, polymer gels are considered reliable as a three-dimensional dosimeter. This work used polymer MAGIC-gel sealed in 2 mm thin-wall glass spheres to assess the three-dimensional (3D) dose distribution imparted to patients and compared the results with that provided by the treatment planning system. Four SBRT treatments targeting vertebral, ilium, pelvic lymph node and lung regions were selected for this study. A computed tomography (CT) scan of each glass sphere was obtained, and the patient treatment plan was superimposed on the glass sphere CT image. Thereafter, the spheres were irradiated under similar conditions to the patient using a Varian TrueBeam linear accelerator. A high-spatial resolution optical CT scanner was used to read the glass sphere containing the gel. Planned and delivered 3D dose distributions were compared quantitatively through 3D gamma passing rates at several selected acceptance criteria and qualitatively through the evaluation of dose-profiles, isodose-curves, and dose-volume histograms. We observed that the overall 3D gamma passing rate exceeded 90% at acceptance criteria of 2% dose difference and 2 mm distance-to-agreement for a dose threshold of 20%. The results of this study suggest that the polymer MAGIC-gel sealed in thin-wall glass spheres in conjunction with the optical CT readout method is a suitable PSQA system for SBRT treatments.

Characterisation and application of three-dimensional silicone-based radiochromic dosimetry in 1.5 T magnetic resonance imaging-guided radiotherapy

The magnetic field in magnetic resonance imaging-guided radiotherapy (MRgRT) systems influences the three-dimensional (3D) dose deposition and hence the delivered dose distributions. The aim of this study was to investigate the dose-rate dependency and dose response of silicone-based radiochromic dosimeters for photon irradiation in the precense of a magnetic field using a 1.5 T MRgRT system. Additionally, the study aimed to provide a proof of the concept of radiotherapy treatment based on a treatment plan calculated on magnetic resonance imaging rather than a computed tomography (CT) scan. The delivered dose was read out in 3D with an optical CT scanner and the dose distribution was verified using gamma analysis. We found an insignificant dose-rate dependency for dose rates ranging from 3.2 to 5.1 Gy/min and a linear dose response up to 20 Gy. A 3D 3%/3mm gamma analysis showed a pass rate of 95.1%. The dosimeter showed clinical potential for 3D dose verification of MRgRT delivery.

Bare spherical gel dosimeter with optical computed tomography scanning

Radiochromic polyvinyl alcohol-iodide (PVA-I) hydrogel dosimeter with crosslinking by glutaraldehyde (GTA) has been reported. Because of the transparent gel’s mechanical strength, a study to cast samples in spherical shapes was initiated. The bare sample, 47 mm in diameter was mounted on a funnel and held by suction in a custom, 96 mm diameter, cylindrical vessel for 3D optical CT scanning. A solution of the same formulation without GTA provided refractive index matching inside the vessel for optic scanning and eliminated concentration gradients. The gel sphere remained in the vessel after draining the solution for the ‘in-air’ irradiation. A 20 Gy, maximum dose to the gel sphere was delivered by a single, 6 MV, x-ray beam. Comparison of central axis depth doses for the gel reconstruction and Monte Carlo calculation revealed similar results, indicating accurate 3D dosimetry within 1 mm of the gel surface will be possible. The gel recorded slightly greater dose in build-up region and slightly lower dose in the exit hemisphere relative to the calculation.

Modified optical computed tomography scanner for low temperature scanning

Large radiochromic hydrogels, such as ferrous xylenol formulations require several hours to warm from the storage temperature of 278 K to 293 K for optical CT scanning and irradiation. This warm-up time can be avoided if gels are scanned at 278 K, resulting in a more practical 3D dose measurement. In this study a Vista 16 optical CT scanner was modified to allow scanning at 278 K, below the temperature where condensation forms on the aquarium windows. The refractive index matching liquid was first cooled to 276K in order to cool the aquarium as it was filled. The modification involved pumping cool, dry air into the aquarium scanner compartment to provide a positive pressure, preventing condensation on the aquarium windows. A warming rate of 2 K per hour was achieved with passive cooling which relied on the liquid-filled aquarium’s thermal mass. The radiochromic reaction rate decreased with temperature, requiring an increased post-irradiation wait time from 1 hour at 293 K to 1.5 hours at 278 K. In addition, initial sample transmission was greater by avoiding the auto-darkening that occurred as the samples were warmed from 278 K to 293 K over several hours. This increase in transmission resulted in a larger dynamic range for the dosimeter system.

Preliminary commissioning of a prototype solid tank optical CT scanner for 3D radiation dosimetry

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters. In previous research, it was shown that a design could significantly reduce the volume of the refractive index baths that are commonly found in optical CT systems. The proposed scanner has been manufactured and is in process of being commissioned. The rays refract through the system and their paths are estimated using a ray-tracing simulator. Reconstruction is preformed through algebraic reconstruction technique and iterated using the FISTA-TV algorithm. A Sylgard®184 edge phantom was created to commission the scanner’s spatial resolution. The scanner is capable of a 0.929 mm−1 spatial resolution, although the spatial resolution is highly dependent on the number of iterations, and method of processing the edge spread function.

Feasibility evaluation of N-Isopropyl Acrylamide 3D gel dosimeters for proton therapy.

This study aimed to investigate the feasibility of applying 3D gel dosimeters for proton therapy. Two different formulations (5-5-3-5, 5-3-3-10) for the N-Isopropyl Acrylamide (NIPAM) polymer gel were used to find the best composition for the application of NIPAM polymer gels for proton therapy. The reaction of the gel under different physical conditions, including dependence on energy and dependence on the dose rate of the NIPAM gel under proton irradiation, was also explored. A NIPAM gel dosimeter was used to record the 3D dose distribution, and a self-developed parallel beam optical computed tomography scanner was used to obtain non-irradiated and post-irradiated gel phantom images. The NIPAM gel was filled into a cylindrical acrylic phantom. The results showed that the optical density of the irradiated NIPAM dosimeter was linear in the dose range of 0 to 6 Gy, and the linearity of the two NIPAM gel formulations at the depth of the dose point (2 cm) was 0.98 to 0.89. The dose depth curves showed different patterns with different gel sensitivities. This study demonstrated that the NIPAM gel dosimeter with the 5-3-3-10 formulation is suitable for verifying the dosimetry dose of proton beams.

Commissioning of a solid tank design for fan-beam optical CT based 3D radiation dosimetry.

Objective.Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters used in the verification of complex radiotherapy treatments. In previous work, a novel fan-beam optical CT scanner design was proposed that could significantly reduce the volume of the refractive index baths that are commonly found in optical CT systems. Here, the proposed scanner has been manufactured and commissioned.Approach.Image reconstruction is performed through algebraic reconstruction technique and iterated using the fast iterative shrinkage-thresholding algorithm (FISTA) algorithm. Ray tracing for algebraic reconstruction was performed using an in-house developed ray tracing simulator. A set of Sylgard® 184 phantoms were created to commission spatial resolution, geometric deformity, contrast-to-noise ratio (CNR), and scan settings.Main Results.The scanner is capable of a 0.929 mm-1spatial resolution, observed at 200 iterations, although the spatial resolution is highly dependent on the number of iterations. The geometric distortion, measured by scanning a needle phantom with the prototype scanner as well as a conventional x-ray CT was found to be within <0.25 mm. The CNR was found to peak between 65 and 190 occurring between 50 and 100 iterations and was highly dependent on the region chosen for background noise calculation. The proposed scanner is capable of scanning and reading out slices in less than 1 min per slice.Significance.This work displays the viability of a fan-beam optical CT scanner with minimal index matching using ray-traced algebraic reconstruction.

End-to-end quality assurance for stereotactic radiotherapy with Fricke-Xylenol orange-Gelatin gel dosimeter and dual-wavelength cone-beam optical CT readout

PurposeThe end-to-end (E2E) quality assurance (QA) test is a unique tool for validating the treatment chain undergone by patients in external radiotherapy. It should be conducted in three dimensions (3D) to get accurate results. This study aims to implement these tests with Fricke-Xylenol orange-Gelatin (FXG) gel dosimeter and a newly developed dual-wavelength reading method on the Vista16™ optical Computed Tomography (CT) scanner (ModusQA) for three treatment techniques in stereotactic radiotherapy, on Novalis (Varian) and CyberKnife (Accuray) linear accelerators. MethodsThe tests were performed in head phantoms. Gel measurements were compared with planned dose distributions and measured by film and ion chamber measurements by plotting isodose curves and dose profiles, and by conducting a 3D local gamma-index analysis (2%/2mm criteria). ResultsGamma passing rates were higher than 95 %. Point dose differences between treatment planning and gel and ion chamber measurements at the isocenter were < 2.3 % for both treatments delivered on the Novalis accelerator, while this difference was higher than 4 % for the treatment delivered on the CyberKnife, highlighting a small overdosing of the tumor volume. A good agreement was observed between gel and film dose profiles. ConclusionsThis study presents the successful implementation of 3D E2E QA tests for stereotactic radiotherapy with FXG gel dosimetry and a dual-wavelength reading method on an optical CT scanner. This dosimetric method provides 3D absolute dose distributions in the 0.25 – 10 Gy dose range with a high spatial resolution and a dose uncertainty of around 2 % (k=1).

Fricke-Xylenol orange-Gelatin gel characterization with dual wavelength cone-beam optical CT scanner for applications in stereotactic and dynamic radiotherapy

PurposeThis study is about the development of a new dual wavelength reading method of Fricke-Xylenol orange-Gelatin (FXG) gel dosimeters on the Vista16™ optical Computed Tomography (CT) scanner to perform 3D dose distribution measurements in stereotactic and dynamic radiotherapy treatments. MethodsThe dosimetric characteristics of an optimized FXG gel composition and its optical CT readout have been evaluated. A dual wavelength reading method has been developed on the CT scanner at wavelengths 590 nm and 633 nm. Small-field dose profile measurements with FXG gel and microDiamond (PTW) detectors were compared by γ-index analysis (0.5%/0.5 mm) to validate this method. ResultsThis reading method exhibits linear calibration curves in the 0–4 Gy and 2–10 Gy dose ranges at 590 nm and 633 nm respectively. The absorbed dose values below 4 Gy, measured at 590 nm, and those above 4 Gy, measured at 633 nm, are combined to plot a complete profile. A γ passing rate of 93.4% was achieved. ConclusionsThe new reading method of FXG gel dosimeters has been implemented on the Vista16™ scanner to span absorbed doses representative of stereotactic and dynamic radiotherapy treatments and enable 3D measurements in tumor volumes and surrounding healthy tissues. Small-field profile measurements validated this reading method as FXG gel dosimeters and microDiamond detectors were in very close agreement. This dosimetric method is a promising candidate for 3D quality assurance end-to-end tests in stereotactic and dynamic radiotherapy.

Simulated design optimization of a prototype solid tank optical CT scanner for 3D radiation dosimetry

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters. There exist many prototype designs, as well as some commercial optical CT scanners that have showcased the value that gel dosimeters can provide to improve 3D dose verification for radiation treatments. However, due to factors including image accuracy, scan time, or demanding setup and maintenance there is currently no single scanner that has become a ubiquitous staple in a clinical setting. In this work, a prototype solid tank optical CT scanner is proposed that minimizes the need for a refractive index bath commonly found in optical CT systems. In addition to the design proposal, a ray-path simulator was created to optimize the design such that the solid tank geometry improves light collection across the detector array, maximizes the volume of the dosimeter scanned, and maximizes the dynamic range of the scanner.

MAGIC-f gel dosimeter reading: a comparison between an in-house optical CT and MRI imaging

Introduction: According to new developments in radiation therapy techniques, accurate ‎dose verification in three-dimensions has become more critical. Polymer gel dosimeters ‎‎(PGDs) are valuable tools to be used for this purpose. Nowadays, various imaging ‎modalities are employed to read out the gels. This study was aimed to investigate the ‎measured dose distribution recorded in MAGIC-f PGD with optical computed tomography ‎‎(OCT) by comparison with MRI. ‎Material and methods: We developed an in-house CCD based cone-beam OCT scanner. A ‎phantom of MAGIC-f PGD was used to measure a four-field box dose distribution. MRI and ‎OCT scanners were performed for gel readouts. Both measurement results were compared ‎by gamma index analysis with various acceptance criteria. The temporal stability of the gel ‎was also evaluated with the OCT readout system.‎Results: The percentage of isodose lines from two measured datasets agreed well together. ‎The pass rates were 99.02%, 96.8%, and 89.8% with 5%/5mm, 4%/4mm, and 3%/3mm ‎criteria, respectively, at the phantom's central axial slice. ‎Conclusion: The results indicate that the performance of this OCT system is almost the ‎same with acceptable discrepancies to the MRI as accepted standard readout modality, and ‎it can be used for three-dimensional dose verifications.‎

Accuracy Comparison of the Optical 3D Scanner and CT Scanner

During the last years, due to the dynamic development of the non-contact measurement methods, there has been observed still increasing number of their applications in various fields - not only in the engineering industry. E.g. from the dimensional quality point of view, knowledge of real 3D data of a given part is truly very important. There are several options for obtaining these data such as the usage of optical 3D digitization or computed tomography (CT). However, within the mutual comparability of such data, it is very important to know not only the accuracy of acquiring 3D data, but also e.g. possibilities of these systems in terms of own measurement. In the paper, a specially designed part containing various convex and concave shapes was measured by using two different systems (ATOS TripleScan optical 3D scanner and METROTOM 1500 G2 CT scanner). The resulting scanned models were then compared not only in terms of dimensional accuracy, but also in terms of quality and detail of the obtained data or the time required to prepare the measurement and its implementation.

Optimization of solid tank design for fan-beam optical CT based 3D radiation dosimetry

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters for 3D radiation dosimetry. There exist multiple scanner designs that have showcased excellent 3D dose verification capabilities of optical CT gel dosimetry. However, due to multiple experimental and reconstruction based factors there is currently no single scanner that has become a preferred standard. A significant challenge with setup and maintenance can be attributed to maintaining a large refractive index bath (1–15 l). In this work, a prototype solid ‘tank’ optical CT scanner is proposed that minimizes the volume of refractive index bath to between 10 and 35 ml. A ray-path simulator was created to optimize the design such that the solid tank geometry maximizes light collection across the detector array, maximizes the volume of the dosimeter scanned, and maximizes the collected signal dynamic range. An objective function was created to score possible geometries, and was optimized to find a local maximum geometry score from a set of possible design parameters. The design parameters optimized include the block length x bl , bore position x bc , fan-laser position x lp , lens block face semi-major axis length x ma , and the lens block face eccentricity x be . For the proposed design it was found that each of these parameters can have a significant effect on the signal collection efficacy within the scanner. Simulations scores are specific to the attenuation characteristics and refractive index of a simulated dosimeter. It was found that for a FlexyDos3D dosimeter, the ideal values for each of the five variables were: x bl = 314 mm, x bc = 6.5 mm, x lp = 50 mm, x ma = 66 mm, and x be = 0. In addition, a ClearView™ dosimeter was found to have ideal values at: x bl = 204 mm, x bc = 13 mm, x lp = 58 mm, x ma = 69 mm, and x be = 0. The ray simulator can also be used for further design and testing of new, unique and purpose-built optical CT geometries.

Evaluation of the dose distribution of tomotherapy using polymer gel dosimeters and optical computed tomography with ring artifact correction

Helical tomotherapy (HT) can provide highly conformal dose distribution through multiple-beam irradiation. Evaluation of such dose distribution is essential to ensure the quality of radiotherapy. In this study, we evaluated the performance of measuring the 3D dose distribution delivered by the HT using an N-Isopropylacrylamide (NIPAM) polymer gel dosimeter (PGD) and optical computed tomography (CT) with ring artifact correction. The 3D dose distribution of a real clinical case of cerebral arteriovenous malformation was measured using the NIPAM PGD. The irradiated PGD was scanned using an optical CT scanner 24-hr after dose delivery. The ring artifact correction was performed by median filtering of the acquired optical CT images in polar coordinates. The optical CT images without and with ring artifact correction were compared. The converted dose distributions from the optical CT images were compared with those generated from a treatment planning system using a gamma evaluation. Results show that the NIPAM PGD could accurately record the dose distribution delivered by the tomography. Also, ring artifact correction with proper filter length could effectively reduce the artifacts and improve the uniformity of the measured dose distribution. The pass rate of the measured dose distribution calculated using a three-dimensional gamma evaluation with 3%/3 mm criteria from 89.2% to 99.7% after ring artifact correction. We concluded that the NIPAM PGD and optical CT with ring artifact correction could be useful for pre-treatment verification of the HT.

Economic value of optical and X-ray CT scanning in bucking of Scots pine

ABSTRACT In the Nordic countries, trees are typically bucked into logs using harvesters that measure only a two-dimensional diameter profile of the stem. Because the value of a log can vary significantly depending on its shape and internal defects, bucking decisions can in principle be improved by optical scanning of the three-dimensional stem shape, and detection of knots and other features inside the stem by X-ray computed tomography (CT). The objective of this study was to quantify how much the value recovery at a sawmill could be increased, if bucking decisions took advantage of additional measurement data and a sawing simulator to estimate log values. A simulation study on 1582 Scots pine stems was performed to compare bucking based on a two-dimensional diameter profile with bucking that maximises log value based on either optical scanning alone, or both optical and CT scanning. For log positioning, both the traditional “horns-down” position, and value-maximising rotation based on CT scanning were considered. The results show that bucking based on optical scanning alone can potentially increase the value of sawn timber by up to 5%, and CT scanning before bucking provides little additional value for a sawmill using a CT scanner to optimise log rotation.

Cause of cupping artifacts from radiochromic micelle gel dosimeters used in optical CT scanner measurement

When a radiochromic micelle gel dosimeter is employed for optical computed tomography (CT) measurement, cupping (or dishing) artifacts appear at areas irradiated with a high dose. Anti-scatter polarizer correction is employed to remove scatter signals from optical CT data, but cupping remains. Here, measurement conditions for reducing cupping artifacts are investigated. A change in observation wavelength is found to suppress the cupping influence. Measurements involving aqueous dye solutions with varying jar sizes and dye concentrations reveal cupping artifact behavior under various conditions.

Designing and developing an in-house CCD based optical CT scanner for gel dosimetry

Introduction: Measurement of the complex 3D radiation dose distribution created with advanced radiotherapy techniques such as IMRT and SRS became very important. Polymer gel dosimetry (PGD) is proposed method to recording this dose distribution. MRI, X-ray CT, ultrasound, spectrophotometry and optical CT scanners can be used for readout of Polymer gel dosimeters. Although MRI is gold standard readout instrument, but it is costly and time- consuming. Optical CT is faster and has very lower cost than other methods. The aim of this work is designing and developing an in-house fast CCD based optical computed tomography scanner to extract the 3D radiation dose distribution that recorded in irradiated PGDs. Materials and Methods: in this work we used an array of high power LEDs by 650nm wave length as broad beam light source and a CCD camera as large area detector. The image projections of test object that immersed in a water tank and its rotational movement were controlled by a stepper motor was obtained. Image reconstruction carried out in MATLAB environment with the Filtered back projection method. Results: Reconstructed image quality is very promising. And it is comparable to results of the other works. Contrast to Noise Ratio (CNR) of reconstructed images without any filters in the back projection algorithm was 0.41. Using ramp filter with 0.2 cutoff frequency, gained a 1.1 in CNR and using Butterworth filter with cutoff frequency of 0.3 gained a CNR of 1.3. Increasing cutoff frequency for Butterworth filter will degrade noise properties of reconstructed image and CNR goes down to 0.82, which is comparable with similar works. Conclusion: Optical CT readout system is considered one of the best options for gel readings. If we can overcome the problems of reconstructed images with light rays, this system can be useful for fast and accurate readout of irradiated polymer gel dosimeters.

Effect of gold nanoparticles on dose enhancement of 6 Mv X-rayin MAGIC_f polymer gel dosimeter

Introduction: Currently, the potential application of gold nanoparticles (AuNPs) to increase the efficiency of radiation therapy have been investigated. However, the loss of an appropriate method to estimate the dose distribution in nanoparticle laden tissue limits the applicability of nanoparticles in radiotherapy clinics. Polymer gel dosimetry provides an accurate and precise system that enables to measure the dose distribution in full three dimension. In this study, the radiation dose enhancement effect of AuNPs was assessed through gel dosimetry analysis. Materials and Methods: To achieve the mentioned goal, AuNPs were impegrated in MAGIC_f polymer gel dosimeter and irradiated by 6Mv X-ray beam. Irradiated gel was then evaluated by two modalities of Magnetic Resonance Imaging (MRI) and Optical Computed Tomography (OCT). Results: MRI and OCT scanning of the MAGIC_f geles containing 0.1 mM AuNPs demonstrated dose enhancements of 7.8% and 6.8%, respectively. Conclusion: Polymer gel dosimetry has the potential to provide a new platform for investigation and optimization of the applicability of nanoparticles in radiation therapy