We have developed a method that leverages the image‐guidedradiotherapy capabilities of a tomotherapy unit to adapt daily treatments to changes in bladder shape and volume. Each patient receives three treatment‐planningCT scans: empty bladder; partially full bladder; and full bladder. For each scan, the radiation oncologist contours the initial and boost target volumes (PTV1 and PTV2) and organs at risk, and an initial treatment plan is generated to deliver 40 Gy in 20 fractions to PTV1. A second treatment plan is designed to deliver 20 Gy in 10 fractions to PTV2 (a total of six treatment plans per patient). Patients are asked to void immediately before each treatment. An MVCT of the pelvis is performed before each fraction to verify patient position and to assess the bladder volume. If the treating therapist concludes that the patient's bladder extends to within 10 mm of the PTV contour, then the corresponding treatment plan for a larger bladder volume is downloaded and the MVCT is repeated. Approximately 20% of fractions required a treatment change based on perceived bladder volume. Three of four patients treated to‐date have required the use of a larger volume treatment plan at least once, even though they are always instructed to empty their bladders just prior to treatment. Our early experience is that relying on patient compliance for treating “empty bladder” is insufficient to ensure proper target coverage, and that generous internal margins are required to ensure target coverage in the absence of adaptive IGRT capability.