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

Abstract: 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 (n =155, 70.4%), low-volume intermediate-risk (n =63, 28.7%), or high-risk (n =2, 0.9%) prostate cancer were treated with TIPPB between December 2000 and June 2006. Seventy-four (33.6%) patients received short-term (3–6 months) androgen suppression therapy before TIPPB. The median followup for patients free of biochemical failure was of 37.9 months (range, 24.0–84.5 months). Results: The receiver operating characteristic (ROC) analysis established a best-fit cutoff value for the quantifiers D 90 and V 100 of 147Gy and 92%, respectively. The Kaplan–Meier analysis of bRFS at the cutoff value of D 90 =147Gy using the ASTRO, nadir+2, and combined (ASTRO and nadir+2) definitions showed a trend toward statistical significance for the ASTRO (p =0.076) and nadir+2 (p =0.064) definitions and a statistically significant correlation for the combined definition (p =0.033). The corresponding 7-year bRFS for the D 90 >147Gy and D 90 ≤147Gy subsets using the ASTRO, nadir+2, and combined definitions were 96.5% vs. 89.7% (ASTRO, p =0.076); 93.7% vs. 70.5% (nadir+2, p =0.064); and 94.4 vs. 75.5% (combined, p =0.033). The V 100 (%) cutoff value of 92% predicted by the ROC analysis was not significant. Among other cutoff values, only D 90 =140Gy (p =0.050) and D 90 =160Gy (p =0.098) showed a trend toward statistical significance when the nadir+2 and the ASTRO definitions were used. The rest of dosimetric, tumor, and patient parameters did not show statistical correlation with bRFS in the Kaplan–Meier analysis. Conclusions: The cutoff value of D 90 =147Gy obtained on postimplantation Day 0 showed a trend toward significant correlation with bRFS when the standard ASTRO and nadir+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 D 90 =152.9Gy, median V 100 =92.5%). [Copyright &y& Elsevier]