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.