New imaging techniques for brachytherapy

Abstract

Brachytherapy is a form of radiation treatment for cancer that involves the placement of sealed radioactive sources inside or in close proximity to the tumour in order to deliver radiation dose to the cancerous cells. Although the growing use of imaging has improved the quality of treatment the patients receive, there are still challenges to overcome. In cervical brachytherapy the radiation dose is delivered using an applicator. The applicator position is used for treatment planning therefore misplacement of the applicator could result in inaccurate treatment, increased levels of toxicity in healthy tissues and even punctures in the uterus during the insertion process. During the insertion the applicator is not visible therefore the treatment may be compromised. It was shown in previous studies that the applicator displacement between each brachytherapy was greater than 1cm. The main question to achieve applicator tracking was to examine if the electromagnetic tracking system that is used to track the ultrasound probe during image registration could be used to solve this issue. Through this thesis a tracking system methodology was developed and its accuracy was measured in a trial and in clinic. For the phantom trial the magnitude of error was measured to be ≈ 3mm and for the clinical evaluation of the tracking system at Royal Surrey County hospital (RSCH) the magnitude of error was measured to be ≈ 5mm. In prostate brachytherapy a computer tomography (CT) scan is performed to the patient in order to aid the verification process but unfortunately the seeds produce multiple artefacts that make the verification process difficult and sometimes impossible because the contour of the prostate is not clear therefore the dosimetry results are inaccurate. A filter methodology was developed to address that issue by performing exemplar image inpainting for the corrupted portion of post prostate CT images. The filtered images were qualitatively compared with a state of the art filter for reducing metal artefact. Additionally the filter is currently being evaluated in a study where the aim is to measure the inter-observer reliability of contouring the prostate in unfiltered and filtered in post prostate brachytherapy CT scans. Two observers from the RSCH agreed on contouring 11 patient dataset for this study. There are only preliminary results for this study but they do not show any improvements in contouring the prostate. The trial is still on-going therefore more data will show the actual effect of the filter.