Departmental Oral Examination (Thesis Title: "Localized Bladder Dose Accumulation in Relation to Urinary Toxicity in Multi-Fraction Cervical Cancer Brachytherapy")

Event Date and Time: 
Tue, 2016-06-21 10:00 - 12:00
Henn 318
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 

Radiation therapy in the definitive treatment of locally advanced carcinoma of the cervix consists of external beam radiotherapy (EBRT) combined with image-guided high-dose-rate (IG HDR) intracavitary brachytherapy (ICBT). IG HDR-ICBT is a relatively new, advanced form of brachytherapy treatment planning and delivery that still relies largely on dose criteria based either on clinical experience using older techniques, or on limited data. Calculation of cumulative dose received over multiple treatment fractions currently utilizes dose-volume-histograms (DVH), which do not provide information about the spatial distribution of dose within the structures of interest. Since most of the organs at risk (OAR) for this site, like the bladder and rectum, are highly deformable, DVH data summed over multiple treatment fractions do not provide accurate estimates of the cumulative dose to specific regions of the organ, and therefore may not be the most appropriate metric to use in treatment planning and dose assessment.

The primary goal of this thesis was, therefore, to develop methods to more accurately quantify “locally accumulated” dose to the bladder-wall in multi-fraction IG HDR-ICBT for cervical cancer using deformable registration, and to apply these to a study of locally-accumulated dosimetric parameters as predictors of late urinary toxicity. To this end, different deformable image and point-set registration methods were evaluated, using phantom data, for their ability to register bladder-wall contours of various sizes. The best of these was retrospectively applied to point-sets representing the bladder-wall in multiple HDR treatment fractions for 60 cervical cancer patients treated at the BC Cancer Agency. The transformation maps obtained from the registrations were used to calculate cumulative dose parameters for the bladder-wall and the urethral opening to the bladder (bladder neck). Patients were divided into Case and Control groups based on urinary toxicity scores for different symptoms, and the ability of the cumulative parameters to predict toxicity was evaluated.

It was concluded that some locally-cumulative parameters estimated using our method have improved potential for predicting urinary toxicity, as compared to traditional DVH-based parameters, in our data set. In addition, dose to small volumes around the bladder neck was found to be a predictor of incontinence.


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