High-dose regions versus likelihood of cure after prostate brachytherapy.

Purpose: To analyze the effect of high-dose regions on biochemical cancer control rates after prostate brachytherapy.

Methods And Materials: Patients with 1997 American Joint Committee on Cancer clinical Stage T1c-T2a prostate carcinoma (Gleason grade 5-6, prostate-specific antigen level 4-10 ng/mL) were randomized to implantation with 125I (144 Gy) vs. 103Pd (125 Gy, National Institute of Standards and Technology 1999). Isotope implantation was performed by standard techniques, using a modified peripheral loading pattern. Of the 313 patients entered in the protocol, 270 were included in this analysis. The 125I source strength ranged from 0.4 to 0.89 mCi (median, 0.55 mCi), and the 103Pd source strength ranged from 1.3 to 1.6 mCi (median, 1.5 mCi). CT was performed within 4 h after implantation. The dosimetric parameters analyzed included the percentage of the postimplant prostate volume covered by the 100%, 150%, 200%, and 300% prescription dose (V100, V150, V200, and V300, respectively). The median time to the last follow-up for patients without failure was 2.7 years. Freedom from biochemical failure was defined as a serum prostate-specific antigen level of < or =0.5 ng/mL at last follow-up. Patients were censored at last follow-up if their serum prostate-specific antigen level was still decreasing.

Results: The mean V100, V150, V200, and V300 value was 90% (+/-8%), 63% (+/-14), 35% (+/-13%), and 14% (+/-7%), respectively. Patients with a V100 of > or =90% had a 3-year freedom from biochemical failure rate of 96% vs. 87% for those with a V100 of <90% (p=0.0029). Overall, patients with more high-dose regions had a greater chance of biochemical control. However, when only patients with a V100 of > or =90% were analyzed, no relationship was found between higher dose regions and the likelihood of cancer control. This lack of effect on biochemical control was apparent for both isotopes.

Conclusion: High-dose regions do not appear to affect cancer control rates, as long as >90% of the prostate volume is covered by the prescription dose.