Stereotactic body radiotherapy (SBRT) is delivered in much fewer fractions and higher doses than conventional EBRT, thus it is imperative that the treatment is both accurate and precise to ensure treatment of the prostate as well as minimization of radiation to surrounding organs at risk (OAR). Studies have shown that continuous monitoring of prostate position and intervention during treatment is important due to shifts outside of planned prostate position that necessitate corrective interventions. A potentially more cost-effective option than continuous monitoring would be to do an additional mid-treatment image to ensure prostate alignment and correct positioning. The objectives of this study were to 1) assess how time between pre-treatment and mid-treatment CT relates to application of shifts and magnitude of shifts and 2) assess how SpaceOar rectal gel (allows separation of rectal wall from prostate) could affect application and magnitude of shifts.