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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.

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The purpose of this work is to investigate the influence of possible patient movement and anatomy alteration on the quality of delivered prostate US based HDR-brachytherapy. The effect of patient movement and anatomy change (after the needle implantation and 3D image set acquisition) on catheter and organ dislocation and the consequences that this generated on the DVHs, conformity index and on radiobiological parameters. Materials and methods: This work is based on 3D image sets and treatment plans of 48 patients obtained right after the needle implantation (clinical plan is based on this 3D image set) and before and after the irradiation. In our institution the 3D-US based pre-planning, the transperineal implantation of needles using template and the intraoperative planning and irradiation is realized using the real-time dynamic planning system Oncentra Prostate. All pre-plans and all the inverse optimization of clinical plans were based on HIPO using the modulation restriction option. The patient body/OARs/catheters movement are generated from the clinical, pre- and post- irradiation plans and its influence on DVH-, COIN and radiobiological parameters of PTV and OARs are calculated and presented. Results: It is observed a slight decrease of treatment plan quality with increase of time between the clinical image set acquisition and the patient irradiation. Also, we show that the patient body movement/anatomy alteration and/or catheters dislocation results in decreased plan quality; change of values of the COIN, DVH- and radiobiological parameters. Conclusion: The measured mean shift of anatomy and needles (beams) is as low as 1.0mm that is lower by an order of magnitude to values known from external beam irradiation. For high modulated plans as those in HDR Brachytherapy such small shifts result in dosimetric changes which are in general lower than 5%. Our results demonstrate that quality assurance procedures have to be clinically implemented to guarantee anatomy and implant stability of the order of 1mm. This can only be realized without any manipulation of the implant and anatomy as done, for instance in the case of removing the US-probe before treatment delivery or moving the patient from one bed to another for the irradiation purposes / Σκοπός της εργασίας αυτής είναι να διερευνήσει την επιδραση που έχει η πιθανή μετακίνηση του ασθενούς και η αλλαγή της ανατομίας στην ποιότητα της Βραχυθεραπείας. Η μετακίνηση του ασθενούς, οι αλλαγές της ανατομίας ( μετά την εμφύτευση των βελονών και την συλλογή των τρισδιάστατων 3D εικόνων), η μετακίνηση των καθετήρων και των οργάνων επιφέρουν αλλαγές που παρουσιάζονται μέσα από τα ιστογράμματα δόσης - όγκου (DVH), δείκτη συμμορφίας (conformity index) και των ραδιοβιολογικών παραμέτρων. Υλικά και Μέθοδοι: Η μελέτη αυτή βασίζεται στην συλλογή τρισδιάστατων εικόνων υπερήχων (3D set) και στους σχεδιασμούς θεραπείας (treatment plans) από 48 ασθενείς που συλλέχθηκαν σε τρείς φάσεις: μετά την εμφύτευση των καθετήρων (κλινικός σχεδιασμός θεραπείας (clinical plan) βασίζεται σε αυτή την συλλογή 3D εικόνων), πριν την ακτινοβόληση και μετά την ακτινοβόληση.Στην κλινική μας ο προσχεδιασμός της θεραπείας (pre-planing) που βασίζεται στο τρισδιάστατο υπερηχογράφημα (3D-US), η διαπερινεϊκή εμφύτευση των καθετήρων με την βοήθεια του οδηγού template, ο διεγχειρητικός σχεδιασμός της θεραπείας (intraoperative planning) και η ακτινοβόληση πραγματοποιούνται με την χρήση του Real-time dynamic planning system Oncentra Prostate. Όλα τα pre-plans και όλα τα inverse optimization clinical plans βασίζονται στο HIPO χρησιμοποιώντας την επιλογή του modulation restriction. Οι μετακινήσεις του σώματος του ασθενούς/ των ευαίσθητων σε κίνδυνο οργάνων (OARs)/ και των καθετήρων αναπαράγονται από τα clinical, pre και post- irradiation plans. Κατόπιν υπολογίζεται και παρουσιάζεται η επίδρασή τους στο DVH, COIN και στις ραδιοβιολογικές παραμέτρους του όγκου στόχου σχεδιασμού (PTV) και των (OARs). Αποτελέσματα: Παρατηρείται μια ελαφρά μείωση της ποιότητας του σχεδιασμού θεραπείας με την αύξηση του χρόνου μεταξύ του κλινικού σχεδιασμού και της ακτινοβόλησης του ασθενούς. Επίσης παρουσιάζουμε ότι η μετακίνηση του ασθενούς/ η αλλαγή στην ανατομία ή/ και η μετακίνηση των καθετήρων έχει ως αποτέλεσμα στην μείωση της ποιότητας του σχεδιασμού. Έχουμε αλλαγή στις αλλαγές στις τιμές του COIN, του DVH και των ραδιοβιολογικών παραμέτρων. Συμπέρασματα: Η μέση τιμή των μετρούμενων μετακινήσεων της ανατομίας και των βελονών είναι ιδιαίτερα μικρή περίπου 1.0mm σε σύγκριση με τις γνωστές τιμές από την εξωτερική ακτινοθεραπεία. Για τους υψηλής διαμόρφωσης σχεδιασμούς, όπως αυτοί της HDR βραχυθεραπείας, μικρές μετακινήσεις οδηγούν σε δοσιμετρικές αλλαγές γενικά μικρότερες από 5%. Τα αποτελέσματα μας παρουσιάζουν ότι λαμβάνοντας υπόψη τις διαδικασίες εξασφάλισης ποιότητας επιτυγχάνεται η ακινητοποίηση του εμφυτεύματος της τάξης του 1mm. Αυτό μπορεί να επιτευχθεί μόνο με ακινητοποίηση του εμφυτεύματος και της ανατομίας, για παράδειγμα στην περίπτωση όπου μετακινούμε την κεφαλή της συσκευής υπερήχων (US- probe) πριν την ακτινοβόληση ή μετακινώντας τον ασθενή από ένα κρεβάτι σε ένα άλλο για τις ανάγκες τις ακτινοβόλησης.

Background and purpose: Historically HDR brachytherapy treatment planning systems ignore the transit dose in the computation of patient dose. However, the total radiation dose delivered during each treatment cycle is equal to the sum of the static dose and the transit dose and every HDR application therefore results in two radiation doses. Consequently, the absorbed dose to the target volume is more than the prescribed dose as computed during treatment planning. The aim of this study was to determine the magnitude of the transit dose component of two 192Ir HDR brachytherapy units and assess its dosimetric significance. Materials and Methods: Ionization chamber dosimetry systems (well-type and Farmertype ionization chambers) were used to measure the charge generated during the transit of the 192Ir source from a GammaMed and a Nucletron MicroSelectron HDR afterloader using single catheters of lengths 120 cm. Different source configurations were used for the measurements of integrated charge. Two analysis techniques were used for transit time determination: the multiple exposure technique and the graphical solution of zero exposure. The transit time was measured for the total transit of the radioactive source into (entry) and out of (exit) the catheters. Results: A maximum source transit time of 1.7 s was measured. The transit dose depends on the source activity, source configuration, number of treatment fractions, prescription dose and the type of remote afterloader used. It does not depend on the measurement technique, measurement distance or the analysis technique used for transit time determination. Conclusion: A finite transit time increases the radiation dose beyond that due to the programmed source dwell time alone. The significance of the transit dose would increase with a decrease in source dwell time or a higher activity source.

The thesis aims to improve treatment dose accuracy in brachytherapy using a high dose rate (HDR) Ir-192 stepping source and in external beam therapy using intensity modulated radiation therapy (IMRT). For HDR brachytherapy, this has been achieved by investigating dose errors in the near field and the transit dose of the HDR brachytherapy stepping source. For IMRT, this study investigates the volume effect of detectors in the dosimetry of small fields, and the clinical implementation and dosimetric verification of a 6MV photon beam for IMRT. For the study of dose errors in the near field of an HDR brachytherapy stepping source, the dose rate at point P at 0.25 cm in water from the transverse bisector of a straight catheter was calculated with Monte Carlo code MCNP 4.A. The Monte Carlo (MC) results were used to compare with the results calculated with the Nucletron Brachytherapy Planning System (BPS) formalism. Using the MC calculated radial dose function and anisotropy function with the BPS formalism, 1% dose calculation accuracy can be achieved even in the near field with negligible extra demand on computation time. A video method was used to analyse the entrance, exit and the inter-dwell transit speed of the HDR stepping source for different path lengths and step sizes ranging from 2.5 mm to 995 mm. The transit speeds were found to be ranging from 54 to 467 mm/s. The results also show that the manufacturer has attempted to compensate for the effects of inter-dwell transit dose by reducing the actual dwell time of the source. A well-type chamber was used to determine the transit doses. Most of the measured dose differences between stationary and stationary plus inter-dwell source movement were within 2%. The small-field dosimetry study investigates the effect of detector size in the dosimetry of small fields and steep dose gradients with a particular emphasis on IMRT measurements. Due to the finite size of the detector, local discrepancies of more than 10 % are found between calculated cross profiles of intensity modulated beams and intensity modulated profiles measured with film. A method to correct for the spatial response of finite sized detectors and to obtain the

Submitted in fulfillment of the requirements of the degree of the Master of Technology : Radiography, Durban University of Technology, 2014. / Research Aims The purpose of this study is to compare 2D HDR Brachytherapy planning and 3D HDR Brachytherapy planning in terms of dose distribution in order to accurately determine bladder and rectal doses. Further research questions were explored to determine whether relationships existed between Computer Tomography volumes and bladder and rectum dose. Methodology The 30 female patients that volunteered for the study were conveniently selected. Their age and ethnic group did not contribute to their selection. All participants were prepared for cervical HDR Brachytherapy. The Brachytherapy templates were computer generated and treatments were given based on the templates. They then had a Computer Tomography (CT) scan (3D data set) of the pelvis. The computer generated templates for 2D Brachytherapy planning were applied to the CT data set i.e. 2DBP. The plans were optimised to take into consideration the dose to the bladder and the rectum i.e. 3DBP. The 2DBP and the 3DBP were then evaluated in order to determine which method of planning yielded more acceptable dose distributions to the bladder and rectum. Results Significant differences in dose distribution were noted on comparison of 2DBP and 3DBP. A significant relationship was noted in respect of bladder mean dose and rectum mean dose. 3DBP proved to be more efficient in yielding lower mean dose to the bladder and the rectum. Whilst a significant relationship was noted in respect of bladder maximum dose, an insignificant relationship was noted for rectum maximum dose. Therefore, the efficiency of 3DBP to yield lower bladder maximum dose was established but its efficiency to yield lower rectum maximum dose is questionable. This has implications for the management of patients’ with cervical cancer who require cervical Brachytherapy. Recommendations It is imperative that imaging modalities be used for the accurate planning of cervical Brachytherapy. This study recommends that CT be used for HDR Brachytherapy planning by proving its greater efficiency compared to template planning.