In radiation therapy it is very important to accurately measure the amount of radiation delivered. The effectiveness of the treatment depends on delivering the dose with an accuracy of 5% or better. The dosimetry in different clinics must also be consistent. For these reasons national and international calibration protocols have been developed. In the US, the American Association of Physicists in Medicine (AAPM) has published several national dosimetry protocols for the calibration of high-energy photon and electron beams. In this study the absorbed dose-to-water determined according to TG-21 and TG-51 protocols, developed by Task Group 21 and Task Group 51 of the Radiation Therapy of AAPM, are compared. The older protocol, TG-21, is based on exposure calibrated ionization chambers using a ⁶⁰Co beam. Many standards laboratories have started to replace exposure standards with those involving absorbed dose-to-water. The new protocol, TG-51, is based on absorbed dose-to-water calibrated ionization chambers using a ⁶⁰Co beam. Also, there are some differences between the beam quality specifiers and data proposed by the two protocols. A comparison between TG-21 and TG-51 protocols was done by determining the radiation dose rate at a designated distance for 6 and 18 MV photon beams, and 16 and 20 MeV electron beams, generated by Clinac a 2100 C linear accelerator. The cylindrical ionization chambers used in this study were Capintec PR-06G and PR-05. The results of the study show a discrepancy between the absorbed dose-to-water determined according to TG-21 and TG-51 protocols of about 1.4% and 1.7% for 6 and 18 MV photon beams, respectively. Absorbed dose-to-water determined according to TG-21 and TG-51 protocols for 16 MeV energy electron beams agree within 1.8%, while the ones of 20 MeV energy beams agree to within 2.4%. The change from exposure to absorbed dose-to-water calibrated ionization chambers has the largest impact on the differences between TG-21 and TG-51 absorbed dose-to-water, while the change in beam quality specifier and stopping power ratios have only a very small effect on these differences. The TG-51 protocol is very simple, minimizing the chance of mistakes, because it starts with absorbed dose-to-water calibration, while the TG-21 is very complex, starting with the calibration for exposure, which is different from the absorbed dose-to-water, the clinical quantity of interest. The TG-51 protocol allows the determination of a more accurate absorbed dose in a ⁶⁰Co beam than the TG-21 protocol since it uses an absorbed dose-to-water calibration factor directly measured, while the exposure based dosimetry system is dependent on external physical data which are not measured in clinics. / Graduation date: 2003

Diamond has long been the material of interest for radiotherapy dosimetry due to its high sensitivity, radiation hardness and near tissue equivalency. However natural diamond detector has not become a popular choice because of variability among detectors, high cost and response dependence on dose rate. The recent success in synthesizing single crystal diamond has reignited the interest. Synthetic diamond is highly reproducible in purity and electrical properties, combined with small size, it is a suitable candidate for small field dosimetry. A newly available synthetic single crystal diamond detector is being studied to determine the basic dosimetric characteristic and applicability in small field dosimetry. A series of measurements were made in comparison with a 0.125c.c ionization chamber, and two diode detectors. Response of the diamond detector is independent on dose, dose rate and energy. The output factors of small fields determined by the diamond detector is lower than that of the diode detectors and higher than that of the ionization chamber which are known to over response and under response respectively. In percentage depth dose and beam profile measurements, the diamond detector performs similarly with the two diode detectors. It is found that the diamond detector is suitable for small field relative dosimetry. Further investigation is required to study the spatial resolution of the diamond detector in different measurement geometry and the suitability in determining percentage depth dose in the buildup region. / published_or_final_version / Diagnostic Radiology / Master / Master of Medical Sciences

No description available.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 128-139).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1976. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 78-81).

The effect of low closes of radiation is of primary importance if we wish to understand the basic mechanisms of radiation damage. In vitro experiments performed at clinically relevant doses can also lead to better understanding of radiotherapy protocols and fractionation regimes. The availability of accurate data at low doses can facilitate the examination of survival models which describe dose-effect relationships. Most cellular radiobiology experiments are performed at high doses (3 to 30 Cray). The errors in these experiments, while acceptable at high doses, are too large to allow determination of radiobiological parameters, such as oxygen enhancement ratio (OER) and relative biological effectiveness (RBE), at low doses (0 to 3 Cray). These experiments are limited in the low dose region because we are measuring only the surviving fraction, in a population of predominantly surviving cells, and because there is an uncertainty of 10 to 15% in the number of cells plated. We have developed a technique to assay cell survival at low doses. The exact number of cells plated is determined microscopically. After incubation, the number of killed cells and the number of surviving cells are both determined, by microscopic examination. While extremely labour intensive, this technique yields survival data, in the low dose region, which is much more accurate than the data obtained using classical methods. This technique can be used to measure many radiobiological parameters. We have chosen to examine the effect of oxygen at low doses. Our results clearly demonstrate that, for asynchronous Chinese Hamster Ovary (CHO) cells, the radiosensitizing effect of oxygen is reduced at lower doses. A Picker X-ray source (280 kVp, HVL 1.7 mm Cu) was used for these experiments. The choice of a survival model has important implications in the low dose region. The predictions of three different survival models regarding the effect of oxygen at low doses are discussed. This technique can be used to complement the classical "high dose assay" to obtain data that encompasses a large dose range. This will be especially valuable, for example, when attempting to fully describe radiobiological parameters, or when examining survival models. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Radiation dosimetry is necessary for optimising radiation-based medical procedures for individual patients but in the field of nuclear medicine there are few widely available or widely used tools for performing this kind of analysis. Those tools that are available tend to focus on one particular component of the dosimetry problem and integrating tools to form a complete system is left to the end-user. A software system for performing individual, image-based dosimetry analysis of nuclear medicine studies has been developed and validated. The system consists of a suite of tools that use common file formats and data models. The tools can be integrated to form applications by means of a simple scripting system. One tool is a gamma camera simulator that can produce realistic images of dynamic activity distributions in planar or tomographic formats. Simulated imaging studies produced by this tool are used to validate the other tools in the system. In addition, the system implements a method of simulation assisted quantitation which is shown to achieve high accuracy in both software and physical phantom studies. The system is applied to the dosimetry of I-131 Lipiodol, a therapeutic agent used to treat primary and secondary cancers of the liver. Simulation studies are used to validate the analytic methods used. Studies of a series of patients, treated over a period 10 years, are retrospectively analysed using a selection of methods appropriate to the available data. The results of the analysis demonstrated a large range of lung doses from 1 to 10 Gy/GBq administered. The median absorbed dose in liver was 3 Gy (range 1 - 10 Gy) and the median absorbed dose in tumor was 19 Gy (range 5 - 84 Gy). The large individual variation reinforces the necessity of individualised dosimetry for treatment planning and follow up.

Radiation dosimetry is necessary for optimising radiation-based medical procedures for individual patients but in the field of nuclear medicine there are few widely available or widely used tools for performing this kind of analysis. Those tools that are available tend to focus on one particular component of the dosimetry problem and integrating tools to form a complete system is left to the end-user. A software system for performing individual, image-based dosimetry analysis of nuclear medicine studies has been developed and validated. The system consists of a suite of tools that use common file formats and data models. The tools can be integrated to form applications by means of a simple scripting system. One tool is a gamma camera simulator that can produce realistic images of dynamic activity distributions in planar or tomographic formats. Simulated imaging studies produced by this tool are used to validate the other tools in the system. In addition, the system implements a method of simulation assisted quantitation which is shown to achieve high accuracy in both software and physical phantom studies. The system is applied to the dosimetry of I-131 Lipiodol, a therapeutic agent used to treat primary and secondary cancers of the liver. Simulation studies are used to validate the analytic methods used. Studies of a series of patients, treated over a period 10 years, are retrospectively analysed using a selection of methods appropriate to the available data. The results of the analysis demonstrated a large range of lung doses from 1 to 10 Gy/GBq administered. The median absorbed dose in liver was 3 Gy (range 1 - 10 Gy) and the median absorbed dose in tumor was 19 Gy (range 5 - 84 Gy). The large individual variation reinforces the necessity of individualised dosimetry for treatment planning and follow up.