CONCEPTS AND TRENDS IN MEDICAL RADIATION DOSIMETRY: Proceedings of SSD Summer School (original) (raw)
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Review on the characteristics of radiation detectors for dosimetry and imaging
The enormous advances in the understanding of human anatomy, physiology and pathology in recent decades have led to ever-improving methods of disease prevention, diagnosis and treatment. Many of these achievements have been enabled, at least in part, by advances in ionizing radiation detectors. Radiology has been transformed by the implementation of multi-slice CT and digital x-ray imaging systems, with silver halide films now largely obsolete for many applications. Nuclear medicine has benefited from more sensitive, faster and higher-resolution detectors delivering ever-higher SPECT and PET image quality. PET/MR systems have been enabled by the development of gamma ray detectors that can operate in high magnetic fields. These huge advances in imaging have enabled equally impressive steps forward in radiotherapy delivery accuracy, with 4DCT, PET and MRI routinely used in treatment planning and online image guidance provided by cone-beam CT.
Review of four novel dosimeters developed for use in radiotherapy
Journal of Physics: Conference Series, 2013
Centre for Medical Radiation Physics (CMRP) is a research strength at the University of Wollongong, the main research theme of this centre is to develop prototype novel radiation dosimeters. Multiple detector systems have been developed by Prof Rosenfelds' group for various radiation detector applications. This paper focuses on four current detector systems being developed and studied at CMRP. Two silicon array detectors include the magic plate and dose magnifying glass (DMG), the primary focus of these two detectors is high spatial and temporal resolution dosimetry in intensity modulated radiation therapy (IMRT) beams. The third detector discussed is the MOSkin which is a high spatial resolution detector based on MOSFET technology, its primary role is in vivo dosimetry. The fourth detector system discussed is BrachyView, this is a high resolution dose viewing system based on Medipix detector technology.
Fundamentals of Radiation Dosimetry
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The basic concepts of radiation dosimetry are reviewed on basis of ICRU reports and text books. The radiation field is described with, among others, the particle fluence. Cross sections for indirectly ionizing radiation are defined and indicated is how they are related to the mass energy transfer and mass energy absorption coefficients. Definitions of total and restricted mass stopping powers of directly ionizing radiation are given. The dosimetric quantities, kerma, absorbed dose and exposure together with the relations between them are discussed in depth. Finally it is indicated how the absorbed dose can be measured with a calorimeter by measuring the temperature increase and with an ionisation chamber measuring the charge produced by the ionizing radiation and making use of the Bragg-Gray relation.
2002
Most of the radiation effects (in particular biological effects) depend on the microscopic pattern of energy deposition. This fact become apparent if one observes that, although the average energy expended to produce el 1 ementary units of physical damage (ionizations) is fairly independent of particle type and energy, the biological effectiveness of otherwise equal doses of different radiation types may be quite dissimilar. Microdosimetry, the study of the fluctuations of energy deposition and the associated stochastic quantities, was developed to provide a comprehensive description of the spatial and temporal distribution of absorbed energy in irradiated matter. An important step in understanding the radiobiology quality of therapeutic beams is the development of a microdosimeter based on the measurement of deposited energies at a cellular level. Microdosimetry deals with the problem of identifying radiosensitive targets and obtaining the probability of energy deposition therein. Models of radiation action, biological or otherwise, may then be used to convert this information in observable quantities. The aim of this work is the development of a dosimetric prototype system using semiconductors as sensitive material for microdosimetric measurements to determine equivalent doses and energies of incident beams in order to be applied as a support tool in operational routines in radiobiology, radiotherapy, microelectronic and radiation protection. The radiation response of silicon components to neutron fields from nuclear research reactors, IEA-R1 and IPEN-MB1 (thermal, epithermal and fast neutrons), from beam holes, experiments halls, AmBe neutrons source and in the BNCT (Boron Neutron Capture Therapy) Research facility at the IEA-R1 reactor of IPEN/CNEN-SP was investigated.
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Medical Physics, 2006
The development of intensity-modulated radiotherapy (IMRT) has created a clear need for a dosimeter that can accurately and conveniently measure dose distributions in three dimensions to assure treatment quality. PRESAGE™ is a new three dimensional (3D) dosimetry material consisting of an optically clear polyurethane matrix, containing a leuco dye that exhibits a radiochromic response when exposed to ionizing radiation. A number of potential advantages accrue over other gel dosimeters, including insensitivity to oxygen, radiation induced light absorption contrast rather than scattering contrast, and a solid texture amenable to machining to a variety of shapes and sizes without the requirement of an external container. In this paper, we introduce an efficient method to investigate the basic properties of a 3D dosimetry material that exhibits an optical dose response. The method is applied here to study the key aspects of the optical dose response of PRESAGE™: linearity, dose rate dependency, reproducibility, stability, spectral changes in absorption, and temperature effects. PRESAGE™ was prepared in 1×1×4.5 cm 3 optical cuvettes for convenience and was irradiated by both photon and electron beams to different doses, dose rates, and energies. Longer PRESAGE™ columns (2 ×2×13 cm 3) were formed without an external container, for measurements of photon and high energy electron depth-dose curves. A linear optical scanning technique was used to detect the depth distribution of radiation induced optical density (OD) change along the PRESAGE™ columns and cuvettes. Measured depth-OD curves were compared with percent depth dose (PDD). Results indicate that PRESAGE™ has a linear optical response to radiation dose (with a root mean square error of ∼1%), little dependency on dose rate (∼2%), high intrabatch reproducibility (<2%), and can be stable (∼2%) during 2 hours to 2 days post irradiation. Accurate PRESAGE™ dosimetry requires temperature control within 1 °C. Variations in the PRESAGE™ formulation yield corresponding variations in sensitivity, stability, and density. CT numbers in the range 100-470 were observed. In conclusion, the small volume studies presented here indicate PRESAGE™ to be a promising, versatile, and practical new dosimetry material with applicability for radiation therapy.
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The British Journal of Radiology, 1997
A questionnaire was sent out to 57 radiotherapy physics departments in the United Kingdom to determine the type of dosemeters used for in vivo measurements inside and outside X-ray treatment fields, and whether any correction is made for energy dependence when the dose to critical organs outside the main beam is estimated. 44 responses were received. 11 centres used a semiconductor for central axis dosimetry compared with only two centres which used thermoluminescent dosimetry (TLD). 37 centres carried out dosimetry measurements outside the main beam; 25 centres used TLD and 12 centres used a semiconductor detector. Of the 16 centres measuring the dose at both sites, 11 used a semiconductor for the central axis measurement, but only four of those 11 changed to TLD for critical organ dosimetry despite the latter's lower variation in energy response. None of the centres stated that they made a correction for the variation in detector energy response when making measurements outside the main beam, indicating a need for a more detailed evaluation of the energy response of these detectors and the energy spectra outside the main beam.