Relationship between Day 0 dosimetric parameters and biochemical relapse-free survival in patients treated with transperineal permanent prostate interstitial brachytherapy with (125)I seeds

OBJECTIVES
To determine the relationship between dosimetric parameters obtained on postimplantation Day 0 and biochemical relapse-free survival (bRFS) in patients treated with 125I transperineal interstitial permanent prostate brachytherapy (TIPPB).

METHODS
Two-hundred twenty men with low-risk (n5155, 70.4%), low-volume intermediaterisk (n563, 28.7%), or high-risk (n52, 0.9%) prostate cancer were treated with TIPPB between December 2000 and June 2006. Seventy-four (33.6%) patients received short-term (3e6 months) androgen suppression therapy before TIPPB. The median followup for patients free of biochemical failure was of 37.9 months (range, 24.0e84.5 months).

RESULTS
The receiver operating characteristic (ROC) analysis established a best-fit cutoff value for the quantifiers D90 and V100 of 147 Gy and 92%, respectively. The KaplaneMeier analysis of bRFS at the cutoff value of D905147 Gy using the ASTRO, nadir þ 2, and combined (ASTRO and nadir þ 2) definitions showed a trend toward statistical significance for the ASTRO (p50.076) and nadir þ2 (p50.064) definitions and a statistically significant correlation for the combined definition (p50.033).

The corresponding 7-year bRFS for the D90 O147 Gy and D90 <147 Gy subsets using the ASTRO, nadir þ 2, and combined definitions were 96.5% vs. 89.7% (ASTRO, p50.076); 93.7% vs. 70.5% (nadir þ 2, p50.064); and 94.4 vs. 75.5% (combined, p50.033). The V100 (%) cutoff value of 92% predicted by the ROC analysis was not significant. Among other cutoff values, only D905140 Gy (p50.050) and D905160 Gy (p50.098) showed a trend toward statistical significance when the nadir þ 2 and the ASTRO definitions were used. The rest of dosimetric, tumor, and patient parameters did not show statistical correlation with bRFS in the KaplaneMeier analysis.

CONCLUSIONS
The cutoff value of D905147 Gy obtained on postimplantation Day 0 showed a trend toward significant correlation with bRFS when the standard ASTRO and nadir þ 2 definitions were used and a weak but statistically significant correlation with bRFS as per the nonstandard combined definition in a series of patients with predominantly low-risk disease (70.4%) treated at high radiation doses (median D905152.9 Gy, median V100592.5%).

CITATION  Brachytherapy. 2010 Jan-Mar;9(1):8-14