Phase II High Dose Brachytherapy and Low Dose Rate Brachytherapy as Monotherapy in Localized Prostate Cancer

The purpose of this study is to evaluate the dose of High Dose Rate (HDR) brachytherapy chosen for this study as well as a commonly used alternate form of brachytherapy called low dose rate (or seed) brachytherapy. Investigators would like to understand how these treatments control the prostate cancer and look at their short and long term treatment related side effects. The dose of radiation for HDR brachytherapy for this study has been changed since the study started. Other studies using the dose of radiation for HDR brachytherapy that was originally chosen for this study (Arm 2) found that this dose of radiation may be linked to a greater chance of the cancer coming back in the prostate. Therefore since March 2020, for new participants entering the study, a new HDR brachytherapy arm with a higher amount of radiation given over two doses will be tested in this study

Radiation therapy is an accepted treatment to help manage low and intermediate risk prostate cancer. Radiation therapy can be given using machines that are outside the body (called "image guided external beam radiation therapy") or by brachytherapy, which is a form of radiation therapy where the radiation source is placed directly into the prostate gland near the tumour. The standard or usual treatments for low or intermediate risk prostate cancer are low dose-rate (LDR) brachytherapy which involves placing radioactive seeds in the prostate which deliver radiation over several months, image guided external beam radiation therapy (IGRT), or IGRT plus high dose-rate (HDR) brachytherapy boost. High Dose-Rate (HDR) brachytherapy is another type of brachytherapy which delivers a high dose of radiation to the tumour over a period of minutes. The radiation is delivered under computer control through flexible needles, which are temporarily inserted into the prostate. This form of radiotherapy targets cancer cells within the prostate gland. HDR brachytherapy is another type of radiotherapy for prostate cancer that has the potential to help target your cancer more accurately while causing fewer side effects compared with standard radiation therapy. HDR brachytherapy is an option for treatment in some hospitals now but the best dose of radiation is still unknown. This study is testing a new dose of radiation for HDR brachytherapy.