High dose rate afterloading brachytherapy for prostate cancer: catheter and gland movement between fractions.

Fractionated high dose rate afterloading brachytherapy for prostate cancer requires a robust means of catheter fixation with good quality assurance. Catheter position and dosimetry has been formally evaluated in 20 consecutive patients representing a total of 332 catheters undergoing two HDR afterloading brachytherapy fractions over 36 h. The mean interfraction movement of catheters as measured by external length was less than 1 mm, but within the prostate on consecutive CT scans there was a mean interfraction movement of 11.5 mm away from the prostate base. This has a significant impact on implant dosimetry as measured by D90 and the COIN index, unless corrected by repositioning the catheters.