Conformal prostate brachytherapy guided by realtime dynamic dose calculations using permanent 125iodine implants: technical description and preliminary experience.

OBJECTIVE Low dose rate (LDR) prostate brachytherapy (permanent 125I or 103Pd seeds) is an accepted treatment option for low risk prostate cancer patients. However, differences in prostate spatial location, volume and gland deformation between the images obtained during pre-planning and later on during the implant procedure prevent the pre-planned intended dose to be accurately delivered. We are reporting on a new technique based on interactive real-time dynamic intra-operative dose calculation with avoidance of postimplant CT for final dosimetry. The reasons leading us to implementing this new technique are discussed and preliminary results reported. 47-78 years). For the real time intra-operative dosimetric analysis the following values were obtained: a median of 98% (90%-100%) for V90, of 60% (22%-76%) for V150 and 24% (9%-34%) for V200. The median intro-operative D90 obtained was 16,817 cGy with a range of 13,743 to 19,553 cGy. The median dose point calculation to the rectum maximum was 12,936 cGy and for the maximum in urethra was 21,880 cGy. For the real-time dynamic planning, the acute GU grade 1&2 toxicity was reduced from 28% and 2 1% to 16% and 6% respectively. Acute urinary retention was seen in 2/63 or 3% requiring a temporary post-implant bladder catheter. In addition, a decrease in chronic GU grade 1-2 toxicity was also seen from 16% and 17% to 1 1% and 2% respectively. No change in GI toxicity pattern was noted. No severe grade 3-4 intra-operative complications were noted. CONCLUSION Real-time intra-operative planning was successfully implemented in our center. It avoids the possible implant quality and dose delivery disadvantages of the standard post-implant CT-based dosimetry by improving the accuracy of seed placement on real time, which was translated in lower rates of acute and chronic GU morbidity. In addition, avoids the unnecessary time, effort and cost of post-implant CT-based dosimetry.