This thesis details the measurement and simulation of patient skin doses arising from X-ray exposure during interventional cardiology procedures. Interventional cardiology procedures can be long and complex resulting in high skin doses, to the extent that radiation burns may be produced. Twenty patients were used in the study consisting of 10 coronary angiogram and 10 coronary angioplasty procedures. Radiochromic films were used to measure skin dose directly. The Gafchromic® XR-RV2 film was chosen for its suitability for this project. The key characteristics of this film were experimentally determined including: dose response, energy dependence, polarisation and post-exposure growth. The dose range was found to be ideally suited for the doses encountered in this study. Energy dependence was found to be ~14% between 60 and 125 kVp at 1 Gy and introduced an unavoidable uncertainty into dose calculations from unknown beam energies. Document scanner characteristics were also been investigated and a scanning protocol is determined. A mathematical model was created to use the geometry and exposure information encoded into acquisition files to reconstruct dose and dose distributions. The model requires a set of study files encoded according to the DICOM format, as well as user input for fluoroscopic estimations. The output is a dose map and dose summary. Simulation parameters were varied and results compared with film measurements to provide the most accurate model. From the data collected the relation between dose area product, maximum skin dose and fluoroscopic time were also investigated. The results demonstrated that a model based on acquisition information can accurately predict maximum skin dose and provide useful geometrical information. The model is currently being developed into a standalone program for use by the Medical Physics and Bioengineering department.

This thesis details the measurement and simulation of patient skin doses arising from X-ray exposure during interventional cardiology procedures. Interventional cardiology procedures can be long and complex resulting in high skin doses, to the extent that radiation burns may be produced. Twenty patients were used in the study consisting of 10 coronary angiogram and 10 coronary angioplasty procedures. Radiochromic films were used to measure skin dose directly. The Gafchromic® XR-RV2 film was chosen for its suitability for this project. The key characteristics of this film were experimentally determined including: dose response, energy dependence, polarisation and post-exposure growth. The dose range was found to be ideally suited for the doses encountered in this study. Energy dependence was found to be ~14% between 60 and 125 kVp at 1 Gy and introduced an unavoidable uncertainty into dose calculations from unknown beam energies. Document scanner characteristics were also been investigated and a scanning protocol is determined. A mathematical model was created to use the geometry and exposure information encoded into acquisition files to reconstruct dose and dose distributions. The model requires a set of study files encoded according to the DICOM format, as well as user input for fluoroscopic estimations. The output is a dose map and dose summary. Simulation parameters were varied and results compared with film measurements to provide the most accurate model. From the data collected the relation between dose area product, maximum skin dose and fluoroscopic time were also investigated. The results demonstrated that a model based on acquisition information can accurately predict maximum skin dose and provide useful geometrical information. The model is currently being developed into a standalone program for use by the Medical Physics and Bioengineering department.

No description available.

A aferição da dose por técnica de dosimetria in vivo garante que a dose calculada pelo sistema de planejamento seja àquela entregue pelo acelerador linear (AL) durante a radioterapia, garantindo assim os processos de controle de qualidade. O objetivo deste trabalho foi validar a técnica de controle de qualidade em IMRT utilizando filme radiocrômico. Foram analisados 47 planejamentos de IMRT de três regiões: próstata, cabeça e pescoço e crânio. Para cada planejamento utilizouse um filme radiocrômico EBT2 acoplado ao cabeçote do acelerador linear através de uma bandeja preparada para o filme. A leitura e posterior análise da dose pontual e distribuição de dose após 24 horas, foi realizada em sofware desenvolvido em MatLab. O índice de aprovação foi de 92%. Quatro planos foram reprovados em pelo menos 1 critério, sendo 3 de cabeça e pescoço e 1 de crânio. Os resultados da dosimetria in vivo com filme radiocrômico foi validada, podendo ser considerada uma técnica confiável e prática na aferição da dose em radioterapia. / The measurement of dose, using the in vivo technique dosimetry, ensures that the dose calculated by the planning system is exactly the same as the dose delivered in linear accelerator, this ensures quality assurance in radiotherapy. The objective of this study was to evaluate the quality control techinique of IMRT treatments using radiochromic film. We analyzed 47 IMRT plans, which divided into three regions: Prostate, head and neck, and skull. For each plan, we used a radiochromic film coupled in linear accelerator head by a tray prepared to film placement. The film was stored for 24 hours after irradiation. Reading and analysis of point dose and 2D dose distribution were performed after this period. ll plans analyzed, the approval rating was 92%, and the others were flunked at least one criterion. Based on the results obtained in vivo dosimetry with radiochromic film was validated. This technique is reliable and practical to measure the dose delivered by linear accelerator.

A aferição da dose por técnica de dosimetria in vivo garante que a dose calculada pelo sistema de planejamento seja àquela entregue pelo acelerador linear (AL) durante a radioterapia, garantindo assim os processos de controle de qualidade. O objetivo deste trabalho foi validar a técnica de controle de qualidade em IMRT utilizando filme radiocrômico. Foram analisados 47 planejamentos de IMRT de três regiões: próstata, cabeça e pescoço e crânio. Para cada planejamento utilizouse um filme radiocrômico EBT2 acoplado ao cabeçote do acelerador linear através de uma bandeja preparada para o filme. A leitura e posterior análise da dose pontual e distribuição de dose após 24 horas, foi realizada em sofware desenvolvido em MatLab. O índice de aprovação foi de 92%. Quatro planos foram reprovados em pelo menos 1 critério, sendo 3 de cabeça e pescoço e 1 de crânio. Os resultados da dosimetria in vivo com filme radiocrômico foi validada, podendo ser considerada uma técnica confiável e prática na aferição da dose em radioterapia. / The measurement of dose, using the in vivo technique dosimetry, ensures that the dose calculated by the planning system is exactly the same as the dose delivered in linear accelerator, this ensures quality assurance in radiotherapy. The objective of this study was to evaluate the quality control techinique of IMRT treatments using radiochromic film. We analyzed 47 IMRT plans, which divided into three regions: Prostate, head and neck, and skull. For each plan, we used a radiochromic film coupled in linear accelerator head by a tray prepared to film placement. The film was stored for 24 hours after irradiation. Reading and analysis of point dose and 2D dose distribution were performed after this period. ll plans analyzed, the approval rating was 92%, and the others were flunked at least one criterion. Based on the results obtained in vivo dosimetry with radiochromic film was validated. This technique is reliable and practical to measure the dose delivered by linear accelerator.

This project involved designing and building a radiochromic film (RCF) densitometer using a still digital camera as the light detector and light emitting diode, LED, as the light source. The behaviour of the LED and charged coupled device (CCD) in the still digital camera, under different light exposure settings (by changing LED current and camera shutter speed) were measured and an optimal setting was determined. Additionally, methods were devised and tests were carried out in order to spread the illumination area of the single light source. Uniform spreading of the LED illumination area was possible by the use of two diffusers placed at an optimum separation distance that was determined in this work. The usefulness of this custom-made RCF densitometer was demonstrated by using this device to image exposed RCF and using the film analysis software, Image J, to determine the film absorbed dose. Two clinical situations were examined: open and virtual wedge radiation beams. It was concluded that still digital cameras can be used in RCF densitometers provided they can capture and store raw images, a single diffused LED can illumination an area large enough for RCF densitometry and appropriate film analysis software is needed to extract and handle the large volume of greyscale data from the RCF.

Real-time feedback of absorbed dose at a point within a patient can help with radiological quality assurance and innovation. Two radiochromic materials from GafChromic MD-55 and EBT films have been investigated for applicability in real-time in vivo dosimetry of ionizing radiation. Both films were able to produce a real-time measurement of optical density from a small volume, allowing positioning onto a tip of an optical fibre in the future. The increase in optical density was linear with absorbed dose for MD-55, and non-linear for EBT. The non-linearity of EBT is associated with its increased sensitivity to ionizing radiation compared to MD-55, thus reaching optical saturation at a much lower dose. The radiochromic material in EBT film was also shown to polymerize and stabilize faster, decreasing dose rate dependence in real-time measurements in comparison to MD-55. The response of the two media was tested over 75 kVp – 18 MV range of x-ray beams. The optical density measured for EBT was constant within 3% throughout the entire range, while MD-55 exhibited a nearly 40% decrease at low energies. Both materials were also shown to be temperature sensitive, with the change in optical density generally decreasing when the temperature increased from ~22°C to ~37°C. This was accompanied by a shift in the peak absorbance wavelength. It was illustrated that some of this decrease can be corrected for by tracking the peak position and then multiplying the optical density by a correction factor based on the predicted temperature. Overall, the radiochromic material in GafChromic EBT film was found to be a better candidate for in vivo real-time dosimetry than the material in GafChromic MD-55. A novel mathematical model was proposed linking absorbance to physical parameters and processes of the radiochromic materials. The absorbance at every wavelength in the spectrum was represented as a sum of absorbances from multiple absorbers, where absorbance is characterized by its absorption coefficient, initiation constant, and polymerization constant. Preliminary fits of this model to experimental data assuming two absorbers suggested that there is a trade-off between EBT’s greater sensitivity and its dose linearity characteristics. This was confirmed by experimental results.

Real-time feedback of absorbed dose at a point within a patient can help with radiological quality assurance and innovation. Two radiochromic materials from GafChromic MD-55 and EBT films have been investigated for applicability in real-time in vivo dosimetry of ionizing radiation. Both films were able to produce a real-time measurement of optical density from a small volume, allowing positioning onto a tip of an optical fibre in the future. The increase in optical density was linear with absorbed dose for MD-55, and non-linear for EBT. The non-linearity of EBT is associated with its increased sensitivity to ionizing radiation compared to MD-55, thus reaching optical saturation at a much lower dose. The radiochromic material in EBT film was also shown to polymerize and stabilize faster, decreasing dose rate dependence in real-time measurements in comparison to MD-55. The response of the two media was tested over 75 kVp – 18 MV range of x-ray beams. The optical density measured for EBT was constant within 3% throughout the entire range, while MD-55 exhibited a nearly 40% decrease at low energies. Both materials were also shown to be temperature sensitive, with the change in optical density generally decreasing when the temperature increased from ~22°C to ~37°C. This was accompanied by a shift in the peak absorbance wavelength. It was illustrated that some of this decrease can be corrected for by tracking the peak position and then multiplying the optical density by a correction factor based on the predicted temperature. Overall, the radiochromic material in GafChromic EBT film was found to be a better candidate for in vivo real-time dosimetry than the material in GafChromic MD-55. A novel mathematical model was proposed linking absorbance to physical parameters and processes of the radiochromic materials. The absorbance at every wavelength in the spectrum was represented as a sum of absorbances from multiple absorbers, where absorbance is characterized by its absorption coefficient, initiation constant, and polymerization constant. Preliminary fits of this model to experimental data assuming two absorbers suggested that there is a trade-off between EBT’s greater sensitivity and its dose linearity characteristics. This was confirmed by experimental results.

No description available.

Tissue heterogeneity effects present a major challenge to electron beam dosimetry in radiotherapy and radiation protection. The perturbation of the absorbed dose distribution in tissue due to the presence of heterogeneous material boundaries was investigated in this work. Experiments were conducted in a tissue-equivalent phantom in order to quantify electron backscatter from various materials. For these experiments, irradiations were performed using a 6MeV (nominal) electron beam under conditions of one dimensional geometry. Depth-energy degradation of the electron beam provided mean electron energies of 2.3MeV, 1.9MeV, and 1.4MeV at interface locations. Backscatter phenomena were investigated for the following interface geometries: polystyrene/air, polystyrene/cortical-bone-equivalent plastic, polystyrene/copper, and polystyrene/bismuth. Novel radiochromic film dosimetry techniques were developed for these experiments, and the dose and energy response characteristics of GAFChromic Type 37-041 film were investigated. Monte Carlo simulations of the experiments were performed in parallel, using tile ITS TIGER code, and methodologies were developed to determine appropriate input parameters to these simulations. From experimental and Monte Carlo results, the backscatter factor at the interface, its spatial variation with depth, and its dependence on electron energy and scatterer atomic number were investigated. / Thesis / Master of Science (MS)