HDR brachytherapy: improved methods of implementation and quality assurance

Toye, W 2007, HDR brachytherapy: improved methods of implementation and quality assurance, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title HDR brachytherapy: improved methods of implementation and quality assurance
Author(s) Toye, W
Year 2007
Abstract 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 Question s.

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.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Cancer -- Radiotherapy -- Quality control
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