Radiotherapy (RT) is a very effective treatment for cancer, and more than 50% of cancer patients will receive RT as part of their treatment. It is not always possible to deliver tumoricidal doses of RT to pelvic cancers without causing side effects because of the proximity of normal organs. Bladder side effects are common after RT for prostate, gynaecologic and rectal cancer and this can have a serious detrimental effect on survivor quality of life. New techniques that manipulate the spatial distribution of RT dose hold the potential to personalize the design of cancer treatment and provide important opportunities to minimize bladder side effects. But, despite years of investigation, the relationship between bladder dose and the development of side effects remains ill-defined. This is because routine dose calculations do not incorporate the effect of daily bladder filling variations during a 1-2 month RT course and bladder side effects are typically reported using highly subjective symptom scales. This project will capitalize on recent advances in imaging and RT dose modelling to quantify the actual dose delivered to the bladder. This will involve calculating the dose delivered to the bladder each day from images acquired at the time of daily RT, then summing the daily doses using a special technique (deformable registration) which accounts for changes in bladder shape, size and position. Side effects will be assessed through the novel application of various objective methods to measure bladder function (e.g. uroflowmetry, functional MRI). The results of this research will enable the generation of highly personalized RT plans that will provide patients with the highest probability of an uncomplicated cure and will facilitate more uniform reporting of side effects in future clinical trials. Overall, this project has the potential to influence clinical RT practice internationally and reduce the toxicity burden on pelvic cancer survivors worldwide.