skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: SU-F-T-434: Development of a Fan-Beam Optical Scanner Using CMOS Array for Small Field Dosimetry

Abstract

Purpose: To design and construct a second generation optical computed tomography (OCT) system using a fan-beam with a CMOS array detector for the 3D dosimetry with polymer gel and radiochromic solid dosimeters. The system was specifically designed for the small field dosimetry. Methods: The optical scanner used a fan-beam laser, which was produced from a collimated red laser beam (λ=620 nm) with a 15-degree laser-line generating lens. The fan-beam was sent through an index-matching bath which holds the sample stage and a sample. The emerging laser light was detected with a 2.54 cm-long CMOS array detector (512 elements). The sample stage rotated through the full 360 degree projection angles at 0.9-degree increments. Each projection was normalized to the unirradiated sample at the projection angle to correct for imperfections in the dosimeter. A larger sample could be scanned by using a motorized mirror and linearly translating the CMOS detector. The height of the sample stage was varied for a full 3D scanning. The image acquisition and motor motion was controlled by a computer. The 3D image reconstruction was accomplished by a fan-beam reconstruction algorithm. All the software was developed inhouse with MATLAB. Results: The scanner was used on both PRESAGE andmore » PAGAT gel dosimeters. Irreconcilable refraction errors were seen with PAGAT because the fan beam laser line refracted away from the detector when the field was highly varying in 3D. With PRESAGE, this type of error was not seen. Conclusion: We could acquire tomographic images of dose distributions by the new OCT system with both polymer gel and radiochromic solid dosimeters. Preliminary results showed that the system was more suited for radiochromic solid dosimeters since the radiochromic dosimeters exhibited minimal refraction and scattering errors. We are currently working on improving the image quality by thorough characterization of the OCT system.« less

Authors:
; ;  [1];  [2];  [3]
  1. Department of Radiation Oncology, University of Minnesota, Minneapolis, MN (United States)
  2. Department of Physics, Vel Tech University, Chennai (India)
  3. (Mexico)
Publication Date:
OSTI Identifier:
22649027
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; COMPUTER CODES; COMPUTERIZED TOMOGRAPHY; DOSEMETERS; DOSIMETRY; ERRORS; GELS; IMAGE PROCESSING; LASERS; RADIATION DOSE DISTRIBUTIONS; VISIBLE RADIATION

Citation Formats

Brost, E, Warmington, L, Watanabe, Y, Senthilkumar, S, and Departamento de Ingeneria Fisica, DCI, Universidad de Guanajuato, Campus Leon, Guanajuato. SU-F-T-434: Development of a Fan-Beam Optical Scanner Using CMOS Array for Small Field Dosimetry. United States: N. p., 2016. Web. doi:10.1118/1.4956619.
Brost, E, Warmington, L, Watanabe, Y, Senthilkumar, S, & Departamento de Ingeneria Fisica, DCI, Universidad de Guanajuato, Campus Leon, Guanajuato. SU-F-T-434: Development of a Fan-Beam Optical Scanner Using CMOS Array for Small Field Dosimetry. United States. doi:10.1118/1.4956619.
Brost, E, Warmington, L, Watanabe, Y, Senthilkumar, S, and Departamento de Ingeneria Fisica, DCI, Universidad de Guanajuato, Campus Leon, Guanajuato. 2016. "SU-F-T-434: Development of a Fan-Beam Optical Scanner Using CMOS Array for Small Field Dosimetry". United States. doi:10.1118/1.4956619.
@article{osti_22649027,
title = {SU-F-T-434: Development of a Fan-Beam Optical Scanner Using CMOS Array for Small Field Dosimetry},
author = {Brost, E and Warmington, L and Watanabe, Y and Senthilkumar, S and Departamento de Ingeneria Fisica, DCI, Universidad de Guanajuato, Campus Leon, Guanajuato},
abstractNote = {Purpose: To design and construct a second generation optical computed tomography (OCT) system using a fan-beam with a CMOS array detector for the 3D dosimetry with polymer gel and radiochromic solid dosimeters. The system was specifically designed for the small field dosimetry. Methods: The optical scanner used a fan-beam laser, which was produced from a collimated red laser beam (λ=620 nm) with a 15-degree laser-line generating lens. The fan-beam was sent through an index-matching bath which holds the sample stage and a sample. The emerging laser light was detected with a 2.54 cm-long CMOS array detector (512 elements). The sample stage rotated through the full 360 degree projection angles at 0.9-degree increments. Each projection was normalized to the unirradiated sample at the projection angle to correct for imperfections in the dosimeter. A larger sample could be scanned by using a motorized mirror and linearly translating the CMOS detector. The height of the sample stage was varied for a full 3D scanning. The image acquisition and motor motion was controlled by a computer. The 3D image reconstruction was accomplished by a fan-beam reconstruction algorithm. All the software was developed inhouse with MATLAB. Results: The scanner was used on both PRESAGE and PAGAT gel dosimeters. Irreconcilable refraction errors were seen with PAGAT because the fan beam laser line refracted away from the detector when the field was highly varying in 3D. With PRESAGE, this type of error was not seen. Conclusion: We could acquire tomographic images of dose distributions by the new OCT system with both polymer gel and radiochromic solid dosimeters. Preliminary results showed that the system was more suited for radiochromic solid dosimeters since the radiochromic dosimeters exhibited minimal refraction and scattering errors. We are currently working on improving the image quality by thorough characterization of the OCT system.},
doi = {10.1118/1.4956619},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: The objective of this work is to introduce a prototype fan-beam optical computed tomography scanner for three-dimensional (3D) radiation dosimetry. Methods: Two techniques of fan-beam creation were evaluated: a helium-neon laser (HeNe, {lambda} = 543 nm) with line-generating lens, and a laser diode module (LDM, {lambda} = 635 nm) with line-creating head module. Two physical collimator designs were assessed: a single-slot collimator and a multihole collimator. Optimal collimator depth was determined by observing the signal of a single photodiode with varying collimator depths. A method of extending the dynamic range of the system is presented. Two sample types weremore » used for evaluations: nondosimetric absorbent solutions and irradiated polymer gel dosimeters, each housed in 1 liter cylindrical plastic flasks. Imaging protocol investigations were performed to address ring artefacts and image noise. Two image artefact removal techniques were performed in sinogram space. Collimator efficacy was evaluated by imaging highly opaque samples of scatter-based and absorption-based solutions. A noise-based flask registration technique was developed. Two protocols for gel manufacture were examined. Results: The LDM proved advantageous over the HeNe laser due to its reduced noise. Also, the LDM uses a wavelength more suitable for the PRESAGE{sup TM} dosimeter. Collimator depth of 1.5 cm was found to be an optimal balance between scatter rejection, signal strength, and manufacture ease. The multihole collimator is capable of maintaining accurate scatter-rejection to high levels of opacity with scatter-based solutions (T < 0.015%). Imaging protocol investigations support the need for preirradiation and postirradiation scanning to reduce reflection-based ring artefacts and to accommodate flask imperfections and gel inhomogeneities. Artefact removal techniques in sinogram space eliminate streaking artefacts and reduce ring artefacts of up to {approx}40% in magnitude. The flask registration technique was shown to achieve submillimetre and subdegree placement accuracy. Dosimetry protocol investigations emphasize the need to allow gel dosimeters to cool gradually and to be scanned while at room temperature. Preliminary tests show that considerable noise reduction can be achieved with sinogram filtering and by binning image pixels into more clinically relevant grid sizes. Conclusions: This paper describes a new optical CT scanner for 3D radiation dosimetry. Tests demonstrate that it is capable of imaging both absorption-based and scatter-based samples of high opacities. Imaging protocol and gel dosimeter manufacture techniques have been adapted to produce optimal reconstruction results. These optimal results will require suitable filtering and binning techniques for noise reduction purposes.« less
  • A novel method that can greatly improve the dosimetric sensitivity limit of a radiochromic film (RCF) through use of a set of color components, e.g., red and green, outputs from a RGB color scanner has been developed. RCFs are known to have microscopic and macroscopic nonuniformities, which come from the thickness variations in the film's active radiochromic layer and coating. These variations in the response make the optical signal-to-noise ratio lower, resulting in lower film sensitivity. To mitigate the effects of RCF nonuniform response, an optical common-mode rejection (CMR) was developed. The CMR compensates nonuniform response by creating a ratiomore » of the two signals where the factors common to both numerator and denominator cancel out. The CMR scheme was applied to the mathematical operation of creating a ratio using two components, red and green outputs from a scanner. The two light component lights are neighboring wavebands about 100 nm apart and suffer a common fate, with the exception of wavelength-dependent events, having passed together along common attenuation paths. Two types of dose-response curves as a function of delivered dose ranging from 3.7 mGy to 8.1 Gy for 100 kV x-ray beams were obtained with the optical CMR scheme and the conventional analysis method using red component, respectively. In the range of 3.7 mGy to 81 mGy, the optical densities obtained with the optical CMR showed a good consistency among eight measured samples and an improved consistency with a linear fit within 1 standard deviation of each measured optical densities, while those with the conventional analysis exhibited a large discrepancy among eight samples and did not show a consistency with a linear fit.« less
  • Purpose: An innovative small high intensity electron beams with energies from 6 to 12 MeV is being developed at Argonne National Laboratory to deliver an absorbed dose via a catheter to small malignant and nonmalignant lesions. This study reports on the initial dosimetric characteristics of this electron beam. These include output calibration, percent depth dose, beam profiles and leakage through the catheter. Methods: To simulate the narrow electron beam, the Argonne Wakefield Accelerator is used to produce high energy electron beams. The electron beam from the accelerator is monitored by measuring the current through a transmission coil while the beammore » shape is observed with a fluorescent screen. The dosimetry properties of the electron beam transmitting through bone and tissue-like materials are measured with nanodot optically stimulated luminescent dosimeters and EDR radiographic film. The 6 MV photon beam from a Varian True beam linac is used to calibrate both the OSLDs and the film. Results: The beam characteristics of the 12 MeV beam were measured. The properties of the small diameter, 5 mm, beam differs from that of broad clinical electron beams from radiotherapy linacs. Due to the lack of scatter from the narrow beam, the maximum dose is at the surface and the depth of the 50% depth dose is 35 mm compared to 51 mm for a clinical 12 MeV. The widths of the 90% isodose measured at the surface and depths of 2, 6, 12, and 16 mm varied from 6.6 to 8.8 mm while the widths of the FWHM isodose varied from 7.8 to 25.5 mm. Conclusion: Initial beam measurements show favorable dosimetric properties for its use in treating either small surface or internal lesions, particularly to deliver radiation at the time of surgery to maximize the dose to the lesion and spare normal tissue.« less
  • Purpose: We had developed and evaluated a new dosimetric system for proton therapy using array of fiber-optic Cerenkov radiation sensor (FOCRS) which can measure a percent depth dose (PDD) instantly. In this study, the Bragg peaks and spread out Bragg peak (SOBP) of the proton beams measured by FOCRS array were compared with those measured by an ion chamber. Methods and Method: We fabricated an optical fiber array of FOCRS in a handmade phantom which is composed of poly-methyl methacrylate (PMMA). There are 75 holes of 1mm diameter inside the phantom which is designed to be exposed in direction ofmore » beam when it is emerged in water phantom. The proton beam irradiation was carried out using IBA cyclotron PROTEUS 235 at national cancer center in Korea and a commercial data acquisition system was used to digitize the analog signal. Results: The measured Bragg peak and SOBP for the proton ranges of 7∼ 20 cm were well matched with the result from ion chamber. The comparison results show that the depth of proton beam ranges and the width of SOBP measured by array of FOCRS are comparable with the measurement from multi-layer ion chamber (MLIC) although there are some uncertainty in the measurement of FOCRS array for some specific beam ranges. Conclusion: The newly developed FOCRS array based dosimetric system for proton therapy can efficiently reduce the time and effort needed for proton beam range measurement compared to the conventional method and has the potential to be used for the proton pencil beam application.« less
  • Special care of superficial lesions surrounding critical structures, such as an eye, may require tight margins. When this is the case, small megavoltage electron treatment fields and nonstandard treatment distances become necessary. When the field size is found to be less than the practical range of the electron beam, dosimetric measurements should be performed. This research includes data proving that very small electron fields can be employed for treatment with appropriate beam flatness and penumbra. This is accomplished by first coning down the incident beam to a small field size, then secondly by adding a single lead sheet to themore » patient's skin surface. The aperture of the sheet is required to be greater than 2 x 2 cm{sup 2} in size, and must be cut properly to adequately confine the treatment area.« less