Changes in prostate orientation due to removal of a Foley catheter

PURPOSE: Investigate the impact on prostate orientation caused by use and removal of a Foley catheter, and the dosimetric impact on men prospectively treated with prostate stereotactic body radiotherapy (SBRT). METHODS: Twenty-two men underwent a CT simulation with a Foley in place (FCT), followed immediately by a second treatment planning simulation without the Foley (TPCT). The change in prostate orientation was determined by rigid registration of three implanted transponders between FCT and TPCT and compared to measured orientation changes during treatment. The impact on treatment planning and delivery was investigated by analyzing the measured rotations during treatment relative to both CT scans, and introducing rotations of ±15° in the treatment plan to determine the maximum impact of allowed rotations. RESULTS: > 37 Gy in all but one instance. CONCLUSIONS: Removing a Foley catheter can cause large prostate rotations. There does not appear to be a clear dosimetric benefit to obtaining the CT scan with a Foley catheter to define the urethra given the changes in urethral position from removing the Foley catheter. If urethral sparing is desired without the use of a Foley, utilization of an MRI to define the urethra may be necessary, or a pseudo-urethral planning organ at risk volume (PRV) may be used to limit dosimetric hot spots.