Scintillation Dosimetry Research Articles

SU-FF-T-251: Small Volume Dosimetry with Multiple Scintillation Probes

Purpose: To build a novel matrix dosimeter with high sensitivity, good precision and reproducibility based on plastic scintillation dosimetry. This dosimeter possesses excellent water equivalence as well as linearity to dose, dose rate and energy. Method and Materials: A dosimeter was built by coupling scintillating fibers, chosen for their high collection efficiency, to clear optical fiber. Light measurements were performed with a color CCDcamera in order to compare two techniques to remove the stem effect caused by Cerenkov radiation inside the optical fiber: background subtraction and chromatic filtering. Background subtraction is self‐explanatory while chromatic filtering uses light at two different wavelengths (the green and blue channels of the CCD) to remove the undesired Cerenkov radiation. Irradiations were performed at 6 MV for various doses and field sizes.Results: The dark images of the camera are uniform and variation between pixels represents less than 0.7 % of the signal produced by a dose of 10 cGy. Stem effect caused by Cerenkov radiation ranged from 5 % (5×5 field) to 35 % (30×30 field) of the total signal. Chromatic filtering and background subtraction both allow to extract from the signal the stem effect with a similar precision. Linearity of the system was validated down to 2.5 cGy (1.31 % standard deviation) with 0.0055 cm2 probes. At 10 cGy the standard deviation dropped below 0.6 %. Depth dose curves were also measured with a precision below 1 % compared to ionization chamber measurements.Conclusion: Chromatic filtering removes the necessity of a second optical fiber for background subtraction, therefore increasing the spatial resolution while maintaining a precision below 1 % for most of the dose range. The CCDcamera allows more than 150 detectors in its field of view, which can be used in water, in phantom or in vivo.

SU-FF-T-229: A Test of the 3D Scintillation Dosimetry Method for a Ru-106 Eye Plaque Applicator

Purpose: To describe and test a novel and potentially fast, 3D relative dosimetry method based on the observation of scintillation light from an irradiated liquid scintillator (LS) volume serving simultaneously as a phantom material and as a dose detector medium. Method and Materials: The method, named Three Dimensional Scintillation Dosimetry (3DSD), uses visible light images of the liquid scintillator volume at multiple angles and applies a tomographic algorithm to a series of these images to reconstruct the scintillation light emission density in each voxel of the volume. The method is applied to a Ru-106 eye plaque immersed in a LS volume and the reconstructed relative 3D dose map is compared along selected profiles and planes with radiochromic film (RCF) and diode measurements. Results: The comparison indicates that the 3DSD method agrees with the relative RCF dose distributions for a small (3 mm high by ∼12 mm diameter) part of the volume within 25% for most points. Larger, up to 45 % deviations are observed for fraction of the points due to elongation of the RCF transverse isodose contours, not seen by 3DSD. For a comparison, the spread of the RCF measurements ranges from 10 to 15% within this volume. The method is not accurate close to the edge of the plaque, close to the edges of the scintillator volume and further than ∼9 mm from the plaque surface. Conclusion: 3DSD shows potential for quick 3D relative dosimetry in a small volume with accuracy and resolution comparable to existent 2D techniques. More accurate determination of the point spread function of the system, of the light scatter within the cell, of the dose-rate and energy related quenching effects and enhancement of the algorithm for partially blocked projections are expected to extend accuracy to larger volumes and closer to the applicator edges.

EPR study of radiation stability of organic plastic scintillator for cardiovascular brachytherapy Sr 90–Y 90 beta dosimetry

Nowadays, more than one million percutaneous transluminal coronary angioplasties are being performed annually throughout the world. Restenosis is a significant problem associated with these angioplasty procedures. Radiation treatment with catheter-based β-emitter sources is currently under clinical trial to prevent this problem. Due to fast and worldwide introduction of β-sources for intravascular application, there is a growing interest in the dosimetry aspects. However, accurate dosimetry of β-radiation is more difficult than that of γ-radiation. Suitable detectors are not yet available with accuracy down to a tenth of a millimeter. Conventional measuring systems are not capable of such spatial resolution, except radiochromic film. However, film dosimeters have limited sensitivity and their radiation characteristics are different than those of tissue; therefore dose measurements require corrections. An alternative is to use water-equivalent plastic scintillators. In this work, organic plastic scintillator (BCF-10) dosimetry is studied using the Monte Carlo (MC) technique PENELOPE, and its radiation stability, after irradiation, is experimentally studied through electron paramagnetic resonance (EPR). Depth dose and dose profile are measured and compared to film dosimetry results. The EPR technique shows that the recovery time is dose independent in this kind of fiber and shows good stability.

Plastic scintillation dosimetry for radiation therapy: minimizing capture of Cerenkov radiation noise

Over the last decade, there has been an increased interest in scintillation dosimetry using small water-equivalent plastic scintillators, because of their favourable characteristics when compared with other more commonly used detector systems. Although plastic scintillators have been shown to have many desirable dosimetric properties, as yet there is no successful commercial detector system of this type available for routine clinical use in radiation oncology. The main factor preventing this new technology from realizing its full potential in commercial applications is the maximization of signal coupling efficiency and the minimization of noise capture. A principal constituent of noise is Cerenkov radiation. This study reports the calculated capture of Cerenkov radiation by an optical fibre in the special case where the radiation is generated by a relativistic particle on the fibre axis and the fibre axis is parallel to the Cerenkov cone. The fraction of radiation captured is calculated as a function of the fibre core refractive index and the refractive index difference between the core and the cladding of the fibre for relativistic particles. This is then used to deduce the relative intensity captured for a range of fibre core refractive indices and fibre core–cladding refractive index differences. It is shown that the core refractive index has little effect on the amount of radiation captured compared to the refractive index difference. The implications of this result for the design of radiation therapy plastic scintillation dosimeters are considered.

Plastic scintillation dosimetry: optimization of light collection efficiency

Practical contemporary radiotherapy dosimetry systems used for dose measurement and verification are ionization chambers (which typically have at least a 0.1 cm3 air cavity volume), thermoluminescent dosimeters (TLDs) and silicon diodes. However, during the last decade, there has been an increased interest in scintillation dosimetry using small water-equivalent plastic scintillators, due to their favourable characteristics when compared with other more commonly used detector systems. Although plastic scintillators have been shown to have many desirable dosimetric properties, as yet there is no successful commercial detector system of this type available for routine clinical use in radiation oncology. The objectives of this study are to identify the factors preventing this new technology from realizing its full potential in commercial applications. A definition of signal to noise ratio (S/N) will be proposed for this category of detectors. In doing so the S/N ratio for an early prototype design has been calculated and/or measured. Criteria to optimize the response and sensitivity of this category of detectors are presented.

Dosimetry of a 188rhenium-labeled self-expanding stent for endovascular brachytherapy in peripheral arteries

Purpose: Radioactive stents have been proposed as endovascular irradiation device to prevent in-stent restenosis by inhibiting neointimal proliferation. 32P-stents have been used in several studies so far, but require large-scale labeling procedures and endovascular barotrauma for stent expansion supporting the development of edge restenosis. Purpose of this study was to establish dosimetry of a self-expanding nitinol stent for peripheral vascular disease, which was radiolabeled with 188rhenium ( 188Re) by a dip coating technique. Methods and materials: The surface of nitinol Memotherm FLEXX stents was polymer-coated providing functional NH 2 groups for diethylenetriaminepentaacetic acid (DTPA) binding, providing the ligand for the complexation of 188Re onto the stent surface. Stability of radiolabeling was tested over 48 h using an in vitro blood circulation (Chandler Loop). Radial and longitudinal dose distributions of a radiolabeled stent were obtained with a plastic scintillator dosimetry system. Results: Stents with a length of 30 mm and a diameter of 8 mm were labeled with up to 33 MBq 188Re. A total of 69±4% of the labeled 188Re remained stable on the stent surface after 48 h. Ninety-five percent of the infinitely accumulated dose was supplied to the target tissue within 72 h. Including correction for radioactivity washout from the stent, the infinitely accumulated dose at 1 mm radial distance from the stent surface was 1.85±0.19 Gy/MBq 188Re/cm stent length. Conclusions: We developed a technique for radiolabeling of self-expanding nitinol stents with 188Re by dip coating and formation of 188Re chelate complexes. We provide dosimetry data useful for application of this β-emitting stent for endovascular brachytherapy in peripheral vascular occlusive disease.

Endovascular brachytherapy--treatment planning and radiation protection.

The risk of restenosis, main late effect limiting the success of percutaneous transluminal coronary artery angioplasty, can be reduced significantly by vascular radiotherapy, subsequent to PTCA. This discovery lead to the development of new irradiation techniques. Endovascular brachytherapy is the choice in treatment of coronary artery stenosis. Successful irradiation, however, requires precise treatment planning. This review addresses the physical possibilities and problems of intravascular brachytherapy planning, and the radiobiologically based definition of the target volume and of structures at risk. Recommendations for dose specification, recording and reporting are given. The criteria for selecting a vascular radiotherapy technique are discussed as well as the possibilities of dosimetric treatment planning and quality assurance based on precise plastic scintillator dosimetry and intravascular ultrasound. Radiation protection and safety must be reconsidered prior to the usage of therapeutic radiation sources in the catheter laboratory and for the decision about emergency plans. Finally, the design of clinical trials, the role of medical physicists, and the future of irradiation treatment of stenosis is discussed.

115 - Plastic scintillator dosimetry in regions with restricted secondary electron equilibrium

115 - Plastic scintillator dosimetry in regions with restricted secondary electron equilibrium

Optical filtering and spectral measurements of radiation-induced light in plastic scintillation dosimetry

A small, water-equivalent plastic scintillation detector system has previously been developed for radiation therapy dosimetry. A light signal, proportional to dose, is generated in the scintillator and is transmitted to a remote photomultiplier tube (PMT) via optical fibres. Ionizing radiation also produces light in the fibres, which, if not properly accounted for, could limit the accuracy of the scintillator system. The fibre light is shown to have both a Cerenkov radiation and fluorescent component. The differences in the measured optical spectra of the fibre light and plastic scintillator light lead to the possibility of reducing the fibre light component by optical filtering. Optical spectral measurements of a commercially available orange-emitting plastic scintillator revealed that incomplete light-wavelength-shifting to the orange region of the visible spectrum occurs due to the size of the small scintillators that were used. Spectral measurements of orange and green scintillators with higher concentrations of wavelength-shifting fluor have been performed. Quantitative results indicate that using the highest doped orange scintillator and appropriate optical filter can decrease the fibre light contribution by about 50% when compared to the conventional blue scintillator, non-filtered case in typical radiotherapy dosimetry situations.

Something Old, Something New, Something Basic

Abstract 'Something Old' is a photograph of the organisers of the first Conference on Luminescence Dosimetry held at Stanford University in 1965. 'Something New' is the scintillation dosimetry probe developed at the University of Wisconsin, and now available commercially for in-phantom, in vivo and stereotaxic beam applications. 'Something Basic' is an analysis of the problem of determining the average dose deposited by an electron beam in a flat dosemeter of foil, comparing various analytical approaches with Monte Carlo results.

Discussion: scintillation dosimetry, and an application of it.

Discussion: scintillation dosimetry, and an application of it.