BladdEr Full OR Empty for Pelvic Radiation Therapy

Inclusion Criteria: * Provision of signed and dated informed consent form * Stated willingness to comply with all study procedures and availability for the duration of the study * Persons, aged at least 18 years * Deemed eligible to undergo curative intent radiation therapy for primary GU, GI, or Gyn malignancy of the pelvis. * For participants able to become pregnant: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation * For participants able to cause a pregnancy: use of condoms or other methods to ensure effective contraception with partner Exclusion Criteria: * Pregnancy * Tumor invading the bladder, as judged by the enrolling physician based on available clinical information * Contraindications to radiotherapy, including Crohn's disease and active connective tissue disorders such as scleroderma or uncontrolled lupus * Prior radiation therapy to an area requiring treatment in the present study