a catheter assembly for delivering a radiation source into a body cavity includes a catheter shaft having a distal end and a proximal end . an inflatable balloon is coupled to the catheter shaft between the distal end and the proximal end . a dose delivery lumen extends along the catheter shaft between the proximal end and the distal end . the dose delivery lumen is configured to receive the radiation source . a radioabsorptive portion is surrounded by the inflatable balloon .