There is a wide range of predictive dosimetric factors for I-125 and pd-103 prostate brachytherapy

We have analyzed biochemical control versus multiple dosimetric parameters for a relatively homogeneous group of low-risk patients treated with I-125 or Pd-103.

As of January 2006, 602 patients with clinical stage T1c-T2a prostate carcinoma have been randomized to treatment with either I-125 or Pd-103 brachytherapy. This report focuses on 265 patients who had CT-based dosimetry available, and have a minimum of 2 years of follow-up. Standard postimplant dosimetric parameters were calculated including the V100 and D90, as well as the V50, V75, V150, V200, V300, D50, D75, and D200. Treatment margins were calculated using the premarket Dose Calc Test Application provided by Varian BrachyTherapy.

Almost every DVH-based dosimetric parameter was higher for patients with PSA evidence of disease control compared with those with PSA failure, regardless of isotope. Kaplan-Meier univariate analysis indicates that nearly all dosimetric parameters among patients implanted with Pd-103 were strongly predictive of biochemical control, while parameters in the I-125 group all trended to lower values for patients with biochemical failure.

Our demonstration of some predictive value of nearly all dosimetric parameters is in contrast to the impression one is left with from prior reports, which explicitly or implicitly portray a unique role for D90 or V100. We think that it is important for clinical investigators to look at other dosimetric parameters as part of ongoing clinical investigations because it is likely that dosimetric guidelines can be refined to improve our ability to rate implant quality.