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Modeling optical design parameters for fine stimulation in sciatic nerve of optogenetic mice. Sci Rep 2021; 11:22588. [PMID: 34799602 PMCID: PMC8605010 DOI: 10.1038/s41598-021-01353-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 09/28/2021] [Indexed: 11/08/2022] Open
Abstract
Optogenetics presents an alternative method for interfacing with the nervous system over the gold-standard of electrical stimulation. While electrical stimulation requires electrodes to be surgically embedded in tissue for in vivo studies, optical stimulation offers a less-invasive approach that may yield more specific, localized stimulation. The advent of optogenetic laboratory animals-whose motor neurons can be activated when illuminated with blue light-enables research into refining optical stimulation of the mammalian nervous system where subsets of nerve fibers within a nerve may be stimulated without embedding any device directly into the nerve itself. However, optical stimulation has a major drawback in that light is readily scattered and absorbed in tissue thereby limiting the depth with which a single emission source can penetrate. We hypothesize that the use of multiple, focused light emissions deployed around the circumference of a nerve can overcome these light-scattering limitations. To understand the physical parameters necessary to produce pinpointed light stimulation within a single nerve, we employed a simplified Monte Carlo simulation to estimate the size of nerves where this technique may be successful, as well as the necessary optical lens design for emitters to be used during future in vivo studies. By modeling multiple focused beams, we find that only fascicles within a nerve diameter less than 1 mm are fully accessible to focused optical stimulation; a minimum of 4 light sources is required to generate a photon intensity at a point in a nerve over the initial contact along its surface. To elicit the same effect in larger nerves, focusing lenses would require a numerical aperture [Formula: see text]. These simulations inform on the design of instrumentation capable of stimulating disparate motor neurons in mouse sciatic nerve to control hindlimb movement.
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Alanazi RS, Laref A. Monte Carlo simulations of photodynamic therapy in human blood model. Lasers Med Sci 2021; 37:1515-1529. [PMID: 34453656 DOI: 10.1007/s10103-021-03383-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 07/19/2021] [Indexed: 11/26/2022]
Abstract
This study aims to simulate a therapeutic plan for a normal human blood model under various patho-physiological conditions, such as the development of leukemia/blood diseases, by means of Monte Carlo multilayered simulation. The photosensitizing compound selectively accumulates in the target cells. A superficial treatment of a blood sample was performed at different ratios of oxygen saturation ([Formula: see text]) under the concentration ([Formula: see text] = 30 µM) effect of merocyanine 540 (MC540) in the blood irradiation. This was done under the application of visible light of wavelength ~ [Formula: see text] at an exposure time ~ 60 s. The dose of photodynamic therapy (PDT) was evaluated for the biological damage, leading to necrosis and blood damage during the treatment. In addition, the effect of PDT treatment response in the blood is related to hemoglobin oxygen saturation, resulting in an excellent relationship between the changes caused by the treatment in the blood at a peculiar oxygen saturation rate (for the highest response: [Formula: see text] 50%) and a light dose (LD) of 3.83 [Formula: see text] above the minimal toxicity of normal tissues. The photodynamic dose is related to the depth of necrosis and the time of treatment for the achievement of the LD delivery at the PDT of blood.
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Affiliation(s)
- R S Alanazi
- Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia
- Department of Biomedical Technology, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh, Saudi Arabia
| | - A Laref
- Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
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Light delivery device modelling for homogenous irradiation distribution in photodynamic therapy of non-spherical hollow organs. Photodiagnosis Photodyn Ther 2021; 34:102320. [PMID: 33957275 DOI: 10.1016/j.pdpdt.2021.102320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 04/25/2021] [Accepted: 04/26/2021] [Indexed: 10/21/2022]
Abstract
SIGNIFICANCE Photodynamic therapy (PDT) is a useful treatment for select cancers. Homogeneous illumination is a key factor in the successful application of PDT treatment of tumours in hollow organs. Over illumination may damage normal tissue while under illumination may not ablate the target. BACKGROUND There have been many approaches to provide homogeneous irradiation for PDT treatment of hollow organs, including light-scattering medium and isotropic emitter to diffuse light, a balloon filled with solution to expand the organ wall, and shaped fibres. In most studies, the organ is assumed to be spherical. However, many hollow organs treated by PDT are non-spherical, and the uniformity of azimuthal irradiation remains an unsolved problem for cylindrical light sources. OBJECTIVE Find a design principle for homogeneous irradiation in a non-spherical cavity for PDT treatment. METHOD A PDT light delivery device is modeled by a series of sub light sources placed along the longitudinal axis of an ellipsoid. In order to achieve a homogeneous azimuthal irradiation distribution on the elliptical arc, a cost function is solved by adding modulation coefficient to the emission profile. The coefficient of variation of uniformity (Ucov) describes the statistical dispersion of the variation in irradiation over the ellipsoid to the average value. Ucov is used to evaluate the homogeneity of the azimuthal irradiation distribution. RESULT By minimizing the cost function, we found that the truncated Gaussian function can be chosen as the emission profile to generate homogeneous irradiation profile within an ellipsoid cavity model. The emission profile can be tailored to generate Ucov of 96.7 %. Further discussion shows that the light distribution could be generated practically by a side-emitting optical fibre, a LED array, or moving an isotropic emitter successively. The impact of emission angle of light sub-source is analysed and the irradiation profile from discrete longitudinal emissions is calculated. CONCLUSION Theory analysis and simulation indicate that a cylindrical emitter with a non-uniform longitudinal emission profile (truncated Gaussian functions) results in an approximate homogeneous irradiance profile within an ellipsoidal cavity.
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A diffusion equation based algorithm for determination of the optimal number of fibers used for breast cancer treatment planning in photodynamic therapy. BIOMEDICAL PHOTONICS 2020. [DOI: 10.24931/2413-9432-2019-8-4-17-27] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
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Dupont C, Baert G, Mordon S, Vermandel M. Parallelized Monte-Carlo dosimetry using graphics processing units to model cylindrical diffusers used in photodynamic therapy: From implementation to validation. Photodiagnosis Photodyn Ther 2019; 26:351-360. [DOI: 10.1016/j.pdpdt.2019.04.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 04/12/2019] [Accepted: 04/19/2019] [Indexed: 12/28/2022]
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Jain M, Zellweger M, Wagnières G, van den Bergh H, Cook S, Giraud MN. Photodynamic therapy for the treatment of atherosclerotic plaque: Lost in translation? Cardiovasc Ther 2017; 35. [PMID: 27893195 DOI: 10.1111/1755-5922.12238] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Acute coronary syndrome is a life-threatening condition of utmost clinical importance, which, despite recent progress in the field, is still associated with high morbidity and mortality. Acute coronary syndrome results from a rupture or erosion of vulnerable atherosclerotic plaque with secondary platelet activation and thrombus formation, which leads to partial or complete luminal obstruction of a coronary artery. During the last decade, scientific evidence demonstrated that when an acute coronary event occurs, several nonculprit plaques are in a "vulnerable" state. Among the promising approaches, several investigations provided evidence of photodynamic therapy (PDT)-induced stabilization and regression of atherosclerotic plaque. Significant development of PDT strategies improved its therapeutic outcome. This review addresses PDT's pertinence and major problems/challenges toward its translation to a clinical reality.
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Affiliation(s)
- Manish Jain
- Cardiology, Department of Medicine, University and Hospital of Fribourg, Fribourg, Switzerland
| | - Matthieu Zellweger
- Medical Photonics Group, LCOM-ISIC, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Georges Wagnières
- Medical Photonics Group, LCOM-ISIC, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Hubert van den Bergh
- Medical Photonics Group, LCOM-ISIC, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Stéphane Cook
- Cardiology, Department of Medicine, University and Hospital of Fribourg, Fribourg, Switzerland
| | - Marie-Noelle Giraud
- Cardiology, Department of Medicine, University and Hospital of Fribourg, Fribourg, Switzerland
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Pitzschke A, Bertholet J, Lovisa B, Zellweger M, Wagnières G. Determination of the radiance of cylindrical light diffusers: design of a one-axis charge-coupled device camera-based goniometer setup. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:35004. [PMID: 28280841 DOI: 10.1117/1.jbo.22.3.035004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 02/16/2017] [Indexed: 06/06/2023]
Abstract
A one-axis charge-coupled device camera-based goniometer setup was developed to measure the three-dimensional radiance profile (longitudinal, azimuthal, and polar) of cylindrical light diffusers in air and water. An algorithm was programmed to project the two-dimensional camera data onto the diffuser coordinates. The optical system was designed to achieve a spatial resolution on the diffuser surface in the submillimeter range. The detection threshold of the detector was well below the values of measured radiance. The radiance profiles of an exemplary cylindrical diffuser measured in air showed local deviations in radiance below 10% for wavelengths at 635 and 671 nm. At 808 nm, deviations in radiance became larger, up to 45%, most probable due to the manufacturing process of the diffuser. Radiance profiles measured in water were less Lambertian than in air due to the refractive index matching privileging the radial decoupling of photons from the optical fiber.
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Affiliation(s)
- Andreas Pitzschke
- Swiss Federal Institute of Technology (EPFL), Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
| | - Jenny Bertholet
- Swiss Federal Institute of Technology (EPFL), Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
| | - Blaise Lovisa
- Swiss Federal Institute of Technology (EPFL), Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
| | - Matthieu Zellweger
- Swiss Federal Institute of Technology (EPFL), Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
| | - Georges Wagnières
- Swiss Federal Institute of Technology (EPFL), Institute of Chemical Sciences and Engineering, Lausanne, Switzerland
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Baran TM. Recovery of optical properties using interstitial cylindrical diffusers as source and detector fibers. JOURNAL OF BIOMEDICAL OPTICS 2016; 21:77001. [PMID: 27447954 PMCID: PMC4956772 DOI: 10.1117/1.jbo.21.7.077001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 07/07/2016] [Indexed: 05/26/2023]
Abstract
We demonstrate recovery of optical properties using arrays of interstitial cylindrical diffusing fibers as sources and detectors. A single 1-cm diffuser delivered laser illumination at 665 nm, while seven 1- and 2-cm diffusers at 1-cm grid spacing acted as detectors. Extraction of optical properties from these measurements was based upon a diffusion model of emission and detection distributions for these diffuser fibers, informed by previous measurements of heterogeneous axial detection. Verification of the technique was performed in 15 liquid tissue-simulating phantoms consisting of deionized water, India ink as absorber, and Intralipid 20% as scatterer. For the range of optical properties tested, mean errors were 4.4% for effective attenuation coefficient, 12.6% for absorption coefficient, and 7.6% for reduced scattering coefficient. Error in recovery tended to increase with decreasing transport albedo. For therapeutic techniques involving the delivery of light to locations deep within the body, such as interstitial photodynamic and photothermal therapies, the methods described here would allow the treatment diffuser fibers also to be used as sources and detectors for recovery of optical properties. This would eliminate the need for separately inserted fibers for spectroscopy, reducing clinical complexity and improving the accuracy of treatment planning.
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Affiliation(s)
- Timothy M. Baran
- University of Rochester Medical Center, Department of Imaging Sciences, 601 Elmwood Avenue, Box 648, Rochester, New York 14642, United States
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Hughes MD, Borca-Tasciuc DA, Kaminski DA. Method for modeling radiative transport in luminescent particulate media. APPLIED OPTICS 2016; 55:3251-3260. [PMID: 27140095 DOI: 10.1364/ao.55.003251] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 02/29/2016] [Indexed: 06/05/2023]
Abstract
Modeling radiative transport in luminescent particulate media is important to a variety of applications, from biomedical imaging to solar power harvesting. When absorption and scattering from individual particles must be considered, the description of radiative transport is not straightforward. For large particles and interparticle spacing, geometrical optics can be employed. However, this approach requires accurate knowledge of several particle properties, such as index of refraction and absorption coefficient, along with particle geometry and positioning. Because the determination of these variables is often nontrivial, we developed an approach for modeling radiative transport in such media, which combines two simple experiments with Monte Carlo simulations to determine the particle extinction coefficient (Γ) and the probability of absorption of light by a particle (PA). The method is validated on samples consisting of luminescent phosphor powder dispersed in a silicone matrix.
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Cui H, Zhang T, Yang X. Laser-enhanced cavitation during high intensity focused ultrasound: An in vivo study. APPLIED PHYSICS LETTERS 2013; 102:133702. [PMID: 23653486 PMCID: PMC3631212 DOI: 10.1063/1.4800780] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 03/25/2013] [Indexed: 05/28/2023]
Abstract
Laser-enhanced cavitation during high intensity focused ultrasound (HIFU) was studied in vivo using a small animal model. Laser light was employed to illuminate the sample concurrently with HIFU radiation. The resulting cavitation was detected with a passive cavitation detector. The in vivo measurements were made under different combinations of HIFU treatment depths, laser wavelengths, and HIFU durations. The results demonstrated that concurrent light illumination during HIFU has the potential to enhance cavitation effect by reducing cavitation threshold in vivo.
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Affiliation(s)
- Huizhong Cui
- KU Bioengineering Research Center, Department of Mechanical Engineering, University of Kansas, 1530 W. 15th Street, 5109 Learned Hall, Lawrence, Kansas 66045, USA
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Sassaroli A, Martelli F. Equivalence of four Monte Carlo methods for photon migration in turbid media. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2012. [PMID: 23201658 DOI: 10.1364/josaa.29.002110] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
In the field of photon migration in turbid media, different Monte Carlo methods are usually employed to solve the radiative transfer equation. We consider four different Monte Carlo methods, widely used in the field of tissue optics, that are based on four different ways to build photons' trajectories. We provide both theoretical arguments and numerical results showing the statistical equivalence of the four methods. In the numerical results we compare the temporal point spread functions calculated by the four methods for a wide range of the optical properties in the slab and semi-infinite medium geometry. The convergence of the methods is also briefly discussed.
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Affiliation(s)
- Angelo Sassaroli
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts 02155, USA.
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Baran TM, Foster TH. New Monte Carlo model of cylindrical diffusing fibers illustrates axially heterogeneous fluorescence detection: simulation and experimental validation. JOURNAL OF BIOMEDICAL OPTICS 2011; 16:085003. [PMID: 21895311 PMCID: PMC3166340 DOI: 10.1117/1.3613920] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 06/24/2011] [Accepted: 06/27/2011] [Indexed: 05/22/2023]
Abstract
We present a new Monte Carlo model of cylindrical diffusing fibers that is implemented with a graphics processing unit. Unlike previously published models that approximate the diffuser as a linear array of point sources, this model is based on the construction of these fibers. This allows for accurate determination of fluence distributions and modeling of fluorescence generation and collection. We demonstrate that our model generates fluence profiles similar to a linear array of point sources, but reveals axially heterogeneous fluorescence detection. With axially homogeneous excitation fluence, approximately 90% of detected fluorescence is collected by the proximal third of the diffuser for μ(s)'∕μ(a) = 8 in the tissue and 70 to 88% is collected in this region for μ(s)'∕μ(a) = 80. Increased fluorescence detection by the distal end of the diffuser relative to the center section is also demonstrated. Validation of these results was performed by creating phantoms consisting of layered fluorescent regions. Diffusers were inserted into these layered phantoms and fluorescence spectra were collected. Fits to these spectra show quantitative agreement between simulated fluorescence collection sensitivities and experimental results. These results will be applicable to the use of diffusers as detectors for dosimetry in interstitial photodynamic therapy.
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Affiliation(s)
- Timothy M Baran
- University of Rochester, The Institute of Optics, Rochester, New York 14627, USA
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Zhang S, Wang Y, Wang H, Jiang S, Xie X. Quantitative evaluation of signal integrity for magnetocardiography. Phys Med Biol 2009; 54:4793-802. [DOI: 10.1088/0031-9155/54/15/010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Alerstam E, Andersson-Engels S, Svensson T. White Monte Carlo for time-resolved photon migration. JOURNAL OF BIOMEDICAL OPTICS 2008; 13:041304. [PMID: 19021312 DOI: 10.1117/1.2950319] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
A novel scheme for fully scalable White Monte Carlo (WMC) has been developed and is used as a forward solver in the evaluation of experimental time-resolved spectroscopy. Previously reported scaling problems are avoided by storing detection events individually, turning spatial and temporal binning into post-simulation activities. The approach is suitable for modeling of both interstitial and noninvasive settings (i.e., infinite and semi-infinite geometries). Motivated by an interest in in vivo optical properties of human prostate tissue, we utilize WMC to explore the low albedo regime of time-domain photon migration--a regime where the diffusion approximation of radiative transport theory breaks down, leading to the risk of overestimating both reduced scattering (mu(s)') and absorption (mu(a)). Experimental work supports our findings and establishes the advantages of Monte Carlo-based evaluation.
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Lilge L, Vesselov L, Whittington W. Thin cylindrical diffusers in multimode Ge-doped silica fibers. Lasers Surg Med 2005; 36:245-51. [PMID: 15704158 DOI: 10.1002/lsm.20150] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND OBJECTIVES Cylindrical fiber diffusers are common tools in photodynamic therapy (PDT). However, large outer diameter and short length limit the indications to which they can be applied. Here a diffuser with an outer diameter of 250 microm and an active length exceeding 5 cm was developed. STUDY DESIGN/MATERIALS AND METHODS Diffusers based on photosensitive quartz optical fibers with a cladding diameter of 140 microm were developed using a structured beam from an excimer laser. A complete set of photometric characteristics, including longitudinal, polar, and azimuth radiance emission diagrams were collected. RESULTS AND CONCLUSIONS The longitudinal radiance emission is homogenous to within +/-10%. The ability to create custom designed longitudinal emission profiles was demonstrated. The variations of the polar and azimuth radiance emission diagrams were within +/- 15% from an ideal Lambertian emitter. The polar uniformity can be improved with a slight increase of the outer diameter using a diffusing recoating compound. The residual light leakage at the distal end of the fiber diffuser was suppressed to 2%. The minimal bending radius after recoating is approximately 5 mm. Maximum power distribution is > 0.5 W cm(-1).
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Affiliation(s)
- Lothar Lilge
- University Health Network, 610 University Avenue, Toronto, Ontario, Canada, M5G 2M9.
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Murphy PS, Cosgrove VP, Schwarz AJ, Webb S, Leach MO. Proton spectroscopic imaging of polyacrylamide gel dosimeters for absolute radiation dosimetry. Phys Med Biol 2000; 45:835-45. [PMID: 10795975 DOI: 10.1088/0031-9155/45/4/302] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Proton spectroscopy has been evaluated as a method for quantifying radiation induced changes in polyacrylamide gel dosimeters. A calibration was first performed using BANG-type gel samples receiving uniform doses of 6 MV photons from 0 to 9 Gy in 1 Gy intervals. The peak integral of the acrylic protons belonging to acrylamide and methylenebisacrylamide normalized to the water signal was plotted against absorbed dose. Response was approximately linear within the range 0-7 Gy. A large gel phantom irradiated with three, coplanar 3 x 3 cm square fields to 5.74 Gy at isocentre was then imaged with an echo filter technique to map the distribution of monomers directly. The image, normalized to the water signal, was converted into an absolute dose map. At the isocentre the measured dose was 5.69 Gy (SD = 0.09) which was in good agreement with the planned dose. The measured dose distribution elsewhere in the sample shows greater errors. A T2 derived dose map demonstrated a better relative distribution but gave an overestimate of the dose at isocentre of 18%. The data indicate that MR measurements of monomer concentration can complement T2-based measurements and can be used to verify absolute dose. Compared with the more usual T2 measurements for assessing gel polymerization, monomer concentration analysis is less sensitive to parameters such as gel pH and temperature, which can cause ambiguous relaxation time measurements and erroneous absolute dose calculations.
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Affiliation(s)
- P S Murphy
- Joint Department of Physics, The Institute of Cancer Research, The Royal Marsden NHS Trust, Sutton, Surrey, UK.
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McJury M, Tapper PD, Cosgrove VP, Murphy PS, Griffin S, Leach MO, Webb S, Oldham M. Experimental 3D dosimetry around a high-dose-rate clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter. Phys Med Biol 1999; 44:2431-44. [PMID: 10533920 DOI: 10.1088/0031-9155/44/10/305] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
It is well known that the experimental dosimetry of brachytherapy sources presents a challenge. Depending on the particular-dosimeter used, measurements can suffer from poor spatial resolution (ion chambers), lack of 3D information (film) or errors due to the presence of the dosimeter itself distorting the radiation flux. To avoid these problems, we have investigated the dosimetry of a clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter. Experimental measurements of dose versus radial distance from the centre of the source (cross-line plots) were compared with calculations produced with a Nucletron NPS planning system. Good agreement was found between the planning system and gel measurements in planes selected for analysis. Gel dosimeter measurements in a coronal plane through the phantom showed a mean difference between measured absorbed dose and calculated dose of 0.17 Gy with SD = 0.13 Gy. Spatially, the errors at the reference point remain within one image pixel (1.0 mm). The use of polymer gel dosimetry shows promise for brachytherapy applications, offering complete, three-dimensional dose information, good spatial resolution and small measurement errors. Measurements close to the source, however, are difficult, due to some of the limiting properties of the polyacrylamide gel.
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Affiliation(s)
- M McJury
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden Hospital NHS Trust, Sutton, Surrey, UK
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