Room: Exhibit Hall | Forum 1
Purpose: Intra-operative planning under live ultrasound guidance for prostate seed implants provides flexibility for radiation oncologists to tailor plans to current patient anatomy. The purpose of this study was to assess differences in intra-operative to post-operative dosimetry for a large sample of patients.
Methods: Intraoperative and post-operative treatment plans for 623 prostate cancer patients who received Â¹â?°Â³Pd seeds implanted via the dynamic intraoperative implantation approach were collected. Dosimetric changes between intraoperative and postoperative plans were analyzed via paired students t-test for statistical significant (Î±=0.05). Dosimetric quantities assessed were prostate V100, V150, D90; rectum D2cc, D0.1 cc, urethra D10, D30.
Results: Statistically significant differences were found in all comparisons except prostate V150% (p=0.09). The maximum number of lost seeds was 8 and average was less than 1. Mean intraoperative and postoperative prostate volumes were similar (30.8 and 31.5 cc respectively), but still statistically significant (p<0.01). Mean intraoperative and postoperative prostate D90s were 106.7Â±11.6% and 105.0Â±9.2% respectively, which yielded p<0.01. Though this difference may be considered clinically insignificant, 70/623 (11.2%) postoperative D90s deviated from intraoperative D90s by more than 20%. Sixty (9.6%) patients had intraoperative D90s that deviated by more than 20% from the prescription but postoperative D90s that fell within the Â±20% range. Thirteen patients (2.1%) had the opposite occur.
Conclusion: Though average differences between dosimetric parameters were small and may be considered clinically insignificant, the differences were statistically significant and changes in prostate D90 from intraoperative to postoperative settings may warrant continued utilization of postoperative planning.