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Daily Image Guided Radiation Therapy for Prostate Cancer: An assessment of treatment plan reproducibility.

Doctor of Health Science / It is well documented that for prostate cancer patients undergoing radiation therapy there is a correlation between target volume displacement and changes in bladder and rectal volumes. However, these studies have used a methodology that has captured only a subset of all treatment positions. This research used daily Computer Tomography (CT) imaging to comprehensively assess organ volumes, organ motion and their effect on dose, something that has never been performed previously, thus adding considerably to the understanding of the topic. Daily CT images were obtained using a Siemens Primus Linear Accelerator equipped with an in-room Somatom CT unit in the accelerator suite, marketed as ‘Primatom’, to accurately position the patient prior to treatment delivery. The internal structures of interest were contoured on the planning workstation by the investigator. The daily volume and location of the organs were derived from the computer to assess and analyse internal organ motion. The planned dose distribution was then imported onto the treatment CT datasets and used to compare the planned dose to i) the actual isocentre, where the isocentre was actually placed for that fraction, ii) the uncorrected isocentre, by un-doing any on-line corrections performed by the treatment staff prior to treatment delivery, and iii) the future isocentre, by placing the isocentre relative to internal organ motion on a daily basis. The results of this study did not confirm a statistically significant decrease in rectum volumes over time (hypothesis 1), however large fluctuations in bladder volume were confirmed (hypothesis 2). Internal organ motion for the rectum and bladder was demonstrated to be related to organ filling. Ideal planning volumes for these organs have been reported to minimise systematic and random uncertainty in the treatment volumes. An observed decrease in prostate volume over time, a systematic uncertainty in the location of the prostate at the time of the planning CT scan and a significant relationship between prostate centre of volume and rectum and bladder volumes has resulted in a recommendation that patients should be re-scanned during treatment to ensure appropriate clinical target volume coverage. A significant relationship between rectal and bladder volumes and the dose delivered to these organs was found (hypothesis 3). The dose delivered to the planning target volume was not related to the rectal or bladder volumes, although it was related to the motion of these organs. Despite these results only minimal effects on the dose delivered to any of the three isocentres occurred, indicating that the planned dose was accurately delivered using the methodology presented here (hypothesis 4). However the results do indicate that the patient preparation instructions need to be improved if margins are to be reduced in the future. It is unrealistic to assume that Image Guided Radiation Therapy will ever become routine practice due to infrastructure costs and time limitations. This research will inform radiation therapy centres of the variables associated with prostate cancer treatment on a daily basis, something that has never before been realistically achievable. As a result centres will be able to devise protocols to improve treatment outcomes.
Date January 2006
CreatorsKnight, Kellie Ann
PublisherUniversity of Sydney., Faculty of Health Sciences
Source SetsAustraliasian Digital Theses Program
Detected LanguageEnglish
RightsThe author retains copyright of this thesis.,

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