Inclusion Criteria:  Age older than 17 but less than 81. Non-metastatic prostate cancer patients undergoing definitive radiation treatment. Patients that self-identify as "smartphone owners". Patients with either iPhone (iOS 13.0 or higher) or Android (version 5.0.1 or higher) based smartphone access. English or Spanish speaking patients.  Exclusion Criteria:  Patients with any history of pre-existing urinary retention. Patients with any history of kidney, urothelial tract or bladder cancer. Post-operative prostate patients. Patients that plan to be treated with pelvic lymph node radiation coverage. Patients without a functional bladder. Patients with a history of prior pelvic surgery or penile augmentation (circumcision is okay). Patients who have previously received any form of pelvic radiation. Patients unable to give informed consent. Patients who refuse to drink room-temperature water used for bladder filling. Patients without functional vision. Patients who are colorblind. Patient who refuse to use the smartphone app or who refuse consent.