Health-related quality of life after permanent interstitial brachytherapy for prostate cancer: correlation with postimplant CT scan parameters.

PURPOSE: To determine dosimetric risk factors for increased toxicity after permanent interstitial brachytherapy for prostate cancer. PATIENTS AND METHODS: Quality of life questionnaires (Expanded Prostate Cancer Index Composite) of 60 and 56 patients were analyzed after a median posttreatment time of 6 weeks (A-acute) and 16 months (L-late). The corresponding CT scans were performed 30 days after the implant. The prostate, rectal wall, and base of seminal vesicles were contoured. Prostate volume, number of seeds and needles as well as dosimetric parameters were correlated with the morbidity scores.
RESULTS: For a prostate volume of 38 +/- 12 cm(3) (mean +/- standard deviation), 54 +/- 7 (125)I sources (Rapid Strands), activity of 22.6 +/- 3.0 MBq [0.61 +/- 0.08 mCi]) were implanted using 20 +/- 6 needles. Improved late urinary function scores resulted from a higher number of sources per cm(3) (> or = 1.35). A prostate D(90) < 170 Gy (A)/< 185 Gy (L) and base of seminal vesicle D(10) < 190 Gy (A and L) were associated with higher urinary function scores. Late rectal function scores were significantly higher for patients with a prostate V(200) < 50% and V(150) < 75%. Patients with a prostate volume < 40 cm(3) reached better sexual function scores (A and L). A higher number of needles per cm(3) (> or = 0.5) resulted in improved late urinary, bowel and sexual function scores.
CONCLUSION: Quality of life after a permanent implant can be improved by using an adequate amount of sources and needles. With an increasing number of seeds per cm(3), dose homogeneity is improving. A prostate D(90) < 170 Gy and a base of seminal vesicle D(10) < 190 Gy (as an indicator of the dose to the bladder neck and urethral sphincter) can be recommended to maintain a satisfactory urinary function.