Improving high dose rate and pulsed dose rate prostate brachytherapy : alternative prostate definition and treatment delivery verification methods

Howie, A 2009, Improving high dose rate and pulsed dose rate prostate brachytherapy : alternative prostate definition and treatment delivery verification methods, Masters by Research, Applied Sciences, RMIT University.


Document type: Thesis
Collection: Theses

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Title Improving high dose rate and pulsed dose rate prostate brachytherapy : alternative prostate definition and treatment delivery verification methods
Author(s) Howie, A
Year 2009
Abstract Brachytherapy is a form of radiotherapy in which radioactive sources are placed at short distances from, or even inside the target volume. The use of high dose rate brachytherapy is a widely accepted and clinically proven treatment for some stages of prostate cancer.

The aim of this project was to investigate potential improvements on two of the most important aspects of high dose rate (HDR) and pulsed dose rate (PDR) prostate brachytherapy - prostate definition and treatment delivery verification.

The use of magnetic resonance (MR) imaging in addition to the conventional computed tomography (CT) imaging methods currently used routinely for brachytherapy planning may provide some benefit in accurately defining the prostate and surrounding critical structures. The methods used in this project involved analysis of data sets provided by two Radiation Oncologists.

The results presented showed inter-observer and intra-observer variations in the size and shape of the prostate, as well as analysis of the dosimetric differences that may be reported due to the differences in prostate size and shape. The results also included analysis of critical structure dosimetry - dose to the surrounding radio-sensitive rectum and urethra.

In summary, the results showed that the prostate was defined to be smaller using MR imaging than CT, however the consistency between Oncologists was not significantly improved using MR imaging. MR imaging may be useful in reducing the dose to normal tissue surrounding the prostate and in obtaining better coverage of the smaller target volume, without compromising the critical structures.

The use of LiF:Mg,Ti thermoluminescent dosimeters (TLDs) is a potential avenue for in vivo dose verification of an HDR or PDR prostate brachytherapy treatment plan. This project included a phantom study of these TLDs with the aim to determine their feasibility for clinical use. Cylindrical TLD rods (6 mm length x 1 mm diameter) were used, as these fit inside the brachytherapy needles implanted into the prostate, and therefore had potential to be used clinically to verify the dose delivered in the prostate.

This study was extended to include determination of a correction factor to allow an independent radiation source (6 MV photon beam from a linear accelerator) to be used to obtain control readings for this relative dosimetric method.

The results showed these TLDs to be a promising in vivo dosimeter for prostate brachytherapy with potential errors in the order of 4%. Their potential lies in the fact that they could detect and flag significant calculation errors in treatment plans, and they utilise equipment used routinely for external beam radiotherapy dosimetry in many treatment facilities, reducing the cost of implementing such a procedure.
Degree Masters by Research
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Brachytherapy
HDR
High Dose Rate
PDR
Pulsed Dose Rate
prostate
CT
MRI
TLD
thermoluminescent
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