Abstract : Abstract - The dose distribution among prostate cancer cases is changed according to the conditions of the bladder and rectum filling, which are associated with the radiation's toxicity. This study aims to evaluate the changes in bladder and rectum filling volumes and their effects on dose distribution in external beam radiation therapy for prostate cancer patients. The treatment plans of 28 patients were retrospectively reviewed to compare the difference in planned and received dose for planning target volume (PTV), bladder, rectum, and other organs at risk. Data were then analyzed using the SPSS 24 program. Comparison between planned and achieved doses; D98%, D50%, and D2% for planning target volumes; V60, V56, and V52 for bladder and rectum; maximum dose for bowels and femoral heads; and mean dose used for penial bulbs in both full and empty bladders—showed a significant difference in bladder dose, a minimal difference in planning target volume, and no difference in rectum, bowel, femoral head, and penile bulb dose. Changes in bladder filling volume affect dose distribution. The full bladder and empty rectum protocol was safe and effective. recommended the continuous use of the full bladder and empty rectum protocol and identified a new method to keep the volume of the bladder fixed at all radiotherapy treatment sessions.