A dosimetria in vivo é a verificação final da dose real administrada ao paciente e tornou-se atualmente necessária devido ao aumento da complexidade e da sofisticaçã das técnicas radioterápicas. A finalidade deste trabalho foi apresentar, verificar e avaliar alguns procedimentos básicos, práticos e viáveis para a implementação da dosimetria in vivo com dosímetros termoluminescentes na verificação de dose em um serviço de radioterapia. Para o estabelecimento do sistema dosimétrico termoluminescente, alguns testes e medições foram realizados, incluindo o procedimento de inicialização, a determinação da homogeneidade do grupo de dosímetros, a determinação do fator de correção individual de cada dosímetro, a determinação da faixa de linearidade do sistema e do coeficiente de calibração. Medições em um objeto simulador antropomórfico foram realizadas para garantir que os métodos utilizados são satisfatórios antes que estes fossem usados para medições em pacientes. Medições de dose em um paciente foram feitas em um tratamento de câncer de próstata. A metodologia proposta pode ser usada como parte de um programa de garantia de qualidade em um serviço de radioterapia. / In vivo dosimetry is the ultimate check of the actual dose delivered to an individual patient and has become a procedure actually necessary due to increasing complexity and sophistication of radiotherapy techniques. The purpose of the present work was to present, verify and evaluate some basic, practical and viable procedures for the implementation of in vivo dosimetry with thermoluminescent dosimeters for patient dose verification at a radiotherapy service. For the setting up of the thermoluminescent dosimetric system, several tests and measurements were carried out including the initialisation procedure, the determination of the batch homogeneity, the determination of individual correction factor of each dosimeter, the determination of linearity range of the system and its calibration coefficients. Anthropomorphic phantom measurements were taken to ensure that the methods are satisfactory before they are used for patients measurements. Patient dose measurements were carried out in a prostate cancer treatment. The proposed methodology can be used as a part of a quality assurance program in a radiotherapy service.

O objetivo principal deste trabalho é o de avaliar as possibilidades do uso do osso com dosímetro. O método baseia-se na medida dos centros paramagnéticos criados por ação da radiação ionizante em ossos, utilizando a técnica de ressonância paramagnética eletrônica (RPE). Aplicando este método, foi possível medir doses no intervalo de 10 rad a 3Krad para raios-X e 50 rad a 3 Krad para o raio &#978 Co60. Foi também estabelecido um padrão de preparação das amostras a serem utilizadas como dosímetros. Com este método é possível determinar doses recebidas por indivíduos em casos de acidentes, podendo ser decidido o tipo de tratamento médico a partir do conhecimento destas doses. Outra possível aplicação é a monitoração de tratamento radioterápicos. Foi também estudado o tipo de centro paramagnético criado em ossos por radiação ionizante. / The purpose of this work is to evaluate the possibilities of the use of bone as a dosimeter. This method is based upon measurement of EPR absorption lines intensities f centers created by ionizing radiation. Applying this method it has been possible to measures doses about 10 rad for X rays and 50 rad for &#978 rays of Co60.The methodology for sample preparational has been stablished for use as a dosimeter.With this method it is possible to determine doses received by persons in radiation accidents. Another possible application is the monitoration of radiotherapic treatments. The physical properties of the paramagnetic centers created by radiation was also studied.

This thesis describes experimental work performed (1998-2001) during the author's involvement with the Brachytherapy group at the Peter MacCallum Cancer Centre (PMCC), where he was employed by its Department of Physical Sciences and subsequent modeling and analytical studies. When PMCC added HDR brachytherapy to its radiation therapy practice, an existing operating suite was considered the ideal location for such procedures to be carried out. The integration of brachytherapy into the theatre environment was considered logical due to the relatively invasive nature of brachytherapy techniques and the availability of medical equipment. This thesis contains the detailed study of three key Research Questions involved in clinical aspects relating to quality assurance of an HDR brachytherapy practice. An investigative chapter is dedicated to the pursuit of each of the Research Questions. The first question asked… Is the novel approach to using modular shielding combined with time and distance constraints adequately optimized during HDR brachytherapy? In order to establish optimal clinical practices, this project evaluates the effectiveness of additional shielding added to the modular shielding system without modification of the previously determined time and distance constraints for PMCC staff, other patients, and member of the public. The DOSXYZnrc user code for the EGSnrc Monte Carlo radiation transport code has been used to model exposure pathways to strategic locations used for measurement in and around the operating theatre suite. Modeling allowed exposure pathways to various areas with the facility to be tested without the need to use real sources. The second Research Question asked… How well is dose anisotropy characterized in the near field range of the clinic's HDR 192Ir source? This study experimentally investigated the anisotropy of dose around a 192Ir HDR source in a water phantom using MOSFETs as relative dosimeters. In addition, modeling using the DOSRZnrc user code for the EGSnrc Monte Carlo radiation transport code was performed to provide a complete dose distribution consistent with the MOSFET measurements. Measurements performed for radial distances from 5 to 30 mm extend the range of measurements to 5 mm which has not been previously reported for this source construction. The third Research Question is aimed at the patient level. Is the dose delivered to in vivo dosimeters, located within critical anatomical structures near the prostate, within acceptable clinical tolerance for a large group of HDR prostate patients? An in vivo dosimetry technique employing TLDs to experimentally measure doses delivered to the urethra and rectum during HDR prostate brachytherapy was investigated. Urethral and rectal in vivo measurements for 56 patients have been performed in the initial fraction of four-fraction brachytherapy boost. In the absence of comparable in vivo data, the following local corrective action level was initially proposed: more than 50% of the prostatic urethra receiving a dose 10% beyond the urethral tolerance. The level for investigative action is considered from the analyses of dose differences between measured data and TPS calculation.

<p>Radioiodine has been used in nuclear medicine for the treatment of thyroid diseases such as Thyroid Cancer and Thyrotoxicosis for many years. The treatment renders the patient radioactive. To minimize the dose to the patients’ relatives and the general public, restric-tions are imposed on the behaviour of the patient. This project presents the person dose equivalents actually received by family members of radioiodine patients following such restrictions. The family members wore hospital ID-bands on left and right wrists for up to four weeks. Each ID-band contained two LiF: Mg, Ti Thermo Luminescence Dosimeters (TLD) calibrated to measure air kerma. The TLDs were analysed and a total person dose equivalent received by the relative was calculated from the measured air kerma values. The results were compared to the dose constraints imposed by The Swedish Radiation Protection Authority (SSI FS 2000:3) in order to confirm that the new set of restrictions used at Karolinska University Hospital Huddinge maintains the dose to family members below the applicable limits.</p><p>A total number of 22 relatives were recruited, 8 elderly, 7 adults and 7 children. Of the recruited relatives 4 (2 adults, 2 children) were excluded from the study as they had lost their dosimeter ID-bands or had other reasons not to participate in the study. This leaves the number of relatives used for data analysis at 18 individuals (8 elderly, 5 adults and 5 children) with a min age of 10 years and max age of 80 years.</p><p>The observed average person dose equivalent of 0.43 mSv (max, 1.27; min, 0.12) indi-cates that the new method of individualised restriction used at Karolinska University Hospital Huddinge work as desired in keeping the dose to family members at an accept-able level. The accuracy of the clinical study has been shown to depend greatly on the method by which the dose is investigated but also on the properties of the TLD material used. There is a potential underestimation of air kerma due to fading of up to 30 %. In addition there are contributing uncertainties from both the calibration method and the conversion to person dose equivalent with the combined uncertainty estimated to be 14%.</p>

<p>The International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) operate the IAEA/WHO TLD postal dose audit programme. The purpose of the programme is to verify the beam calibration in radiotherapy centres in developing countries and to check the Secondary Standards Dosimetry Laboratories (SSDLs). Thermoluminescence dosimeters (TLDs) are used as transfer dosimeters and the evaluation of these are done at the IAEA Dosimetry Laboratory. In the present work the uncertainties in the process of dose determination from TLD readings have been evaluated.</p><p>The analysis comprises the TLD reading reproducibility, uncertainties in the calibration coefficient, and uncertainties in factors correcting for fading of TL signal, influence of TLD holder, energy response and dose response non-linearity. The individual uncertainties were combined to estimate the total uncertainty in the evaluated dose from TLD readings. Experimental data from 2001-2005 were used in the analysis.</p><p>The total uncertainty has been estimated to be 1.2 % for irradiations with 60Co -rays and 1.6 % for irradiations with high-energy X-rays. Results from irradiations by the Bureau International des Poids et Mesures (BIPM), Primary Standard Dosimetry Laboratories (PSDLs), Secondary Standard Dosimetry Laboratories (SSDLs) and reference centres compare favourably with the estimated uncertainties.</p><p>The largest uncertainty components are in the energy correction factor (for high-energy X-rays) with a value of 1.1 % and in the dose response non-linearity correction factor with a value of 0.9 %.</p><p>It has been shown that the acceptance limits of 5 % for TLD results of hospitals and 3.5 % for SSDLs are justified when related to the uncertainties in the dose calculations and the uncertainty in the determination of absorbed dose to water at the centre, as discussed in IAEA TRS-398 (IAEA, 2000), provided that it is followed.</p>

Radioiodine has been used in nuclear medicine for the treatment of thyroid diseases such as Thyroid Cancer and Thyrotoxicosis for many years. The treatment renders the patient radioactive. To minimize the dose to the patients’ relatives and the general public, restric-tions are imposed on the behaviour of the patient. This project presents the person dose equivalents actually received by family members of radioiodine patients following such restrictions. The family members wore hospital ID-bands on left and right wrists for up to four weeks. Each ID-band contained two LiF: Mg, Ti Thermo Luminescence Dosimeters (TLD) calibrated to measure air kerma. The TLDs were analysed and a total person dose equivalent received by the relative was calculated from the measured air kerma values. The results were compared to the dose constraints imposed by The Swedish Radiation Protection Authority (SSI FS 2000:3) in order to confirm that the new set of restrictions used at Karolinska University Hospital Huddinge maintains the dose to family members below the applicable limits. A total number of 22 relatives were recruited, 8 elderly, 7 adults and 7 children. Of the recruited relatives 4 (2 adults, 2 children) were excluded from the study as they had lost their dosimeter ID-bands or had other reasons not to participate in the study. This leaves the number of relatives used for data analysis at 18 individuals (8 elderly, 5 adults and 5 children) with a min age of 10 years and max age of 80 years. The observed average person dose equivalent of 0.43 mSv (max, 1.27; min, 0.12) indi-cates that the new method of individualised restriction used at Karolinska University Hospital Huddinge work as desired in keeping the dose to family members at an accept-able level. The accuracy of the clinical study has been shown to depend greatly on the method by which the dose is investigated but also on the properties of the TLD material used. There is a potential underestimation of air kerma due to fading of up to 30 %. In addition there are contributing uncertainties from both the calibration method and the conversion to person dose equivalent with the combined uncertainty estimated to be 14%.

The International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) operate the IAEA/WHO TLD postal dose audit programme. The purpose of the programme is to verify the beam calibration in radiotherapy centres in developing countries and to check the Secondary Standards Dosimetry Laboratories (SSDLs). Thermoluminescence dosimeters (TLDs) are used as transfer dosimeters and the evaluation of these are done at the IAEA Dosimetry Laboratory. In the present work the uncertainties in the process of dose determination from TLD readings have been evaluated. The analysis comprises the TLD reading reproducibility, uncertainties in the calibration coefficient, and uncertainties in factors correcting for fading of TL signal, influence of TLD holder, energy response and dose response non-linearity. The individual uncertainties were combined to estimate the total uncertainty in the evaluated dose from TLD readings. Experimental data from 2001-2005 were used in the analysis. The total uncertainty has been estimated to be 1.2 % for irradiations with 60Co -rays and 1.6 % for irradiations with high-energy X-rays. Results from irradiations by the Bureau International des Poids et Mesures (BIPM), Primary Standard Dosimetry Laboratories (PSDLs), Secondary Standard Dosimetry Laboratories (SSDLs) and reference centres compare favourably with the estimated uncertainties. The largest uncertainty components are in the energy correction factor (for high-energy X-rays) with a value of 1.1 % and in the dose response non-linearity correction factor with a value of 0.9 %. It has been shown that the acceptance limits of 5 % for TLD results of hospitals and 3.5 % for SSDLs are justified when related to the uncertainties in the dose calculations and the uncertainty in the determination of absorbed dose to water at the centre, as discussed in IAEA TRS-398 (IAEA, 2000), provided that it is followed.

Δοσιμετρία είναι ο κλάδος της επιστήμης που ασχολείται με τις μετρήσεις ιοντιζουσών ακτινοβολιών, με σκοπό την ποσοτική έκφραση της σχέσης μεταξύ των χαρακτηριστικών ενός πεδίου ακτινοβόλησης και του αποτελέσματος της ακτινοβόλησης ενός συστήματος. Η δοσιμετρία συνεισφέρει σημαντικά σε όσες επιστήμες κάνουν χρήση ιοντιζουσών ακτινοβολιών, και ιδιαίτερα στο χώρο της Ιατρικής, απ’ όπου και πρωτοξεκίνησε η εφαρμογή της. Υπάρχουν πολλές μέθοδοι δοσιμετρίας, και φυσικά, πολλά διαφορετικά είδη δοσιμέτρων. Στη συγκεκριμένη εργασία θα ασχοληθούμε αποκλειστικά με τη δοσιμετρία θερμοφωταύγειας. Το φαινόμενο της θερμοφωταύγειας βρίσκει πρακτική εφαρμογή στη δοσιμετρία ιοντιζουσών ακτινοβολιών με τη συλλογή των οπτικών φωτονίων που εκπέμπονται κατά την αποδιέγερση του θερμοφωταυγάζοντος υλικού, που χρησιμοποιείται. Η μέθοδος της θερμοφωταύγειας αποτελεί την πιο αξιόπιστη μέθοδο για την μέτρηση δόσεων ακτινοβολίας από ιατρικές εξετάσεις. Οι εφαρμογές της δοσιμετρίας θερμοφωταύγειας στην Ιατρική αφορούν κυρίως μετρήσεις της απορροφούμενης δόσεως στην Ακτινοθεραπεία και την Ακτινοδιαγνωστική, ενώ εφαρμόζεται σε μικρότερο βαθμό και στην Πυρηνική Ιατρική. Σκοπός της συγκεκριμένης εργασίας είναι η μέτρηση δόσεων ασθενών, που υποβάλλονται σε ακτινοδιαγνωστικές εξετάσεις, με τη βοήθεια κρυστάλλων θερμοφωταύγειας. Στην Ακτινοδιαγνωστική, η ανάγκη της δοσιμέτρησης προκύπτει από τις επιταγές της Ακτινοπροστασίας, η οποία απαιτεί τη μικρότερη δυνατή δόση στον ασθενή και το προσωπικό, με την καλύτερη δυνατή ποιότητα απεικόνισης. Κι η ανάγκη αυτή γίνεται πιο επιτακτική, όταν οι ακτινοδιαγνωστικές εξετάσεις αφορούν νεογνά και μικρά παιδιά, καθώς και συγκεκριμένες ομάδες του πληθυσμού που χαρακτηρίζονται από υψηλό βαθμό ακτινοευαισθησίας. Πιο συγκεκριμένα, καλούμαστε να υπολογίσουμε την δόση που λαμβάνουν ασθενείς στον θυροειδή αδένα, όταν υποβάλλονται σε εξέταση οισοφαγογραφήματος που πραγματοποιούνται προκειμένου να ελεγχθεί η φυσιολογία και η λειτουργία του πεπτικού συστήματος. Παράλληλα, καλούμαστε να εκτιμήσουμε τον τυχόν κίνδυνο καρκινογένεσης, λόγω των στοχαστικών αποτελεσμάτων της ακτινοβολίας, έπειτα από συσχέτιση με την τιμή της απορροφούμενης δόσης που προκύπτει. / --

The specific nature of work in nuclear medicine departments involves the use of isotopes and handling procedures, which contribute to the considerable value of the equivalent dose received, in particular, by the fingertips. Workers of nuclear medicine units who label radiopharmaceuticals are exposed to ionizing radiation. The doses of nuclear medicine workers determined by individual dosimeters, which supply data on the magnitude of personal dose equivalent. The dosimetry pointing to a considerable optimization of the radiological protection among that professional group. However, the problem of the excessive hand exposure had been noted already in the early 1980s. Systematic studies were undertaken in West Scotland. The difficulties associated with automation of radiopharmaceutical preparation process are responsible for the continuing growth of exposure to the hands of the workers. Similar studies have also been undertaken, e.g. in Chile, Norway, Australia, Italy, USA, Belgium(1). In each case, special attention has been paid to the exposure of nuclear medicine worker hands. The radiopharmacists who label various ligands can be exposed to high radiation doses to their fingertips (primarily of the thumb, index finger and middle finger). Quite frequently, the Hp(0.07) to the fingertips of those three fingers may exceed the dose limit, i.e. value of 500 mSv/y for the skin of human fingers, this dose limit refers to the maximum dose recorded(2). Specific difficulty in assessing the exposures of the most affected finger parts is aggravated by the fact that the universally employed method for the determination of the radiation doses received by the hands using a ring with attached thermoluminescence detectors is not adequate in this particular case. This measurement method is inadequate because distribution of the doses received by the skin of the hands and fingers is extremely non uniform. The main aim of the study was to measure the absorbed dose at the hands of the personnel by using thermoluminescent detectors / -

Os procedimentos braquiterápicos atuais seguem as diretrizes apresentadas no protocolo da AAPM TG - 43, introduzido em 1995, que define a metodologia de cálculo de dose ao redor de fontes encapsuladas. Este protocolo, dentre outras considerações, adota a água como meio dosimétrico padrão e desconsidera a composição dos tecidos, densidades e dimensões do paciente nas estimativas de dose absorvida. Com o objetivo de realizar os cálculos de dose em condições mais próximas à realidade, a AAPM publicou em 2012 o TG-186, que introduz os algoritmos de cálculos de dose baseados em modelos na braquiterapia (MBDCA- model-based dose calculation algorithm). Estes algoritmos são capazes de considerar as complexidades descritas acima, além de permitirem estimativas de dose diretamente nos tecidos biológicos. Apesar deste advento, ainda há controvérsia sobre a melhor forma de se reportar a dose absorvida, com pontos favoráveis tanto para estimativas de dose na água, quanto nos tecidos. Esta tese se insere dentro deste contexto, buscando a correlação entre todo o conhecimento previamente adquirido baseado em água com os modernos algoritmos de cálculo de dose. A relação entre a dose na água e no meio é realizada através da teoria da cavidade, que assume que a fluência dos fótons na água e no meio é idêntica. Parte dos objetivos do presente trabalho foi avaliar a fluência energética de fótons em diferentes meios irradiados com fontes braquiterápicas de energias baixas (<50,0 keV), propondo uma forma eficiente de correlacionar a dose na água e no meio em situações nas quais a fluência dos fótons é relevante. Avaliou-se a dose absorvida na água e em diferentes tecidos humanos, para quantificar fatores de conversão entre as estimativas de dose, simulados por Monte Carlo. Para validar tais fatores foi proposta uma metodologia experimental com o uso de um objeto simulador, desenvolvido especificamente para a realização deste trabalho e com capacidade de medir os efeitos da heterogeneidade do meio utilizando doses absorvidas em dosímetros termoluminescentes. As correções baseadas na fluência energética obtidas neste estudo, quando necessárias, são capazes de correlacionar a dose absorvida no tecido e na água com uma precisão melhor do que 0,5 % nos casos mais críticos (ex. osso). Os fatores de conversão calculados mostraram que a dose absorvida na água subestima a dose absorvida no osso em até 80 %, mas superestima a dose no tecido adiposo em aproximadamente 75 %, ressaltando a necessidade de se considerar a composição e a densidade do meio nas estimativas de dose. Os resultados experimentais permitiram validar os fatores de conversão de dose simulados com diferenças máximas de 8,5 %, entre os valores experimentais e simulados. Todos os resultados obtidos comprovaram que a estimativa da dose absorvida em procedimentos braquiterápicos com baixas energias diferem significativamente quando realizadas na água e nos tecidos biológicos, evidenciando a necessidade do uso de algoritmos que considerem a heterogeneidade do meio. Tais resultados também enfatizaram a necessidade de se considerar com precisão a composição do corpo, uma vez que variações nas composições médias dos tecidos podem afetar as estimativas dosimétricas e aumentar as incertezas dos resultados. / Brachytherapy treatments are commonly performed using the American Association of Physicists in Medicine (AAPM) Task Group report TG-43, introduced in 1995, which defines the formalism for the calculation of absorbed dose to water, and neglects human tissue densities, material compositions, body interfaces, body shape and dose perturbations from applicators. In order to perform dose calculations in conditions closer to reality, the AAPM published in 2012 the TG-186, which introduces the model-based dose calculation algorithm (MBDCA) in brachytherapy. These algorithms are able to consider the complexities described above, in addition, it allows dose estimates directly into biological tissues. Despite the advent, the best way to report the absorbed dose is still a matter of debate, with favourable points for both water and tissue absorbed dose estimates. The present thesis is inserted within this context, searching for the correlation between all previously acquired knowledge based in absorbed dose to water with the absorbed dose calculated using modern MBDCA. The correlation between the doses in water and the doses in tissue is performed through the cavity theory, which generally assumes that the fluence of the photons in water and in tissue are identical. Part of the purpose of the present work was to evaluate the energy-fluence of photons in different medium irradiated with low energy brachytherapy sources (<50,0 keV), proposing an efficient way to correlate absorbed dose to water and absorbed dose to tissue in brachytherapy in situations in which the fluence of the photons is relevant. In addition to this objective, the dose absorbed in water and in different human tissues was evaluated to quantify conversion factors between these dose estimates, simulated by Monte Carlo. To validate such factors, an experimental methodology was proposed in a phantom with the capacity to quantify the effects of the heterogeneity of the medium measuring absorbed doses in thermoluminescent dosimeters. The energy-fluence based corrections given in this work, when necessary, are able to correlate the absorbed dose to tissue and absorbed dose to water with an accuracy better than 0.5 % in the most critical cases (e.g.: bone tissue). The calculated conversion factors showed that the absorbed dose to water underestimates the absorbed dose to bone by up to 80 % but overestimates the dose in adipose tissue by approximately 75 %, emphasizing the need to consider the composition and the density of tissue in the dose estimates. The experimental results allowed validating the simulated conversion factors with maximum differences of 8.5 % between the experimental and simulated dose values. All the results obtained showed that the estimation of the dose absorbed in low energy brachytherapy procedures differ significantly when performed in water and in biological tissues, evidencing the necessity of using MBDCA. These results also emphasized the need to accurately consider tissue composition, since the smallest variations in tissue compositions may affect dosimetric estimates and increase uncertainties of the results.