ESTRO 2021 Abstract Book

S642

ESTRO 2021

study sought to externally validate a recent study (Crook et al. Radiother Oncol. 149 (2020) 64-69), that proposed 4-year PSA ≤0.2ng/ml as a biochemical threshold of cure in a UK population, by interrogation of the Edinburgh Cancer Centre (ECC) database of the North & Eastern Scottish National Brachytherapy Service. Materials and Methods Patients treated with LDR-BT for PCa at the ECC between 2001 and November 2020 (n = 1142) had baseline demographic, disease, biochemical and serial PSAs prospectively entered into a centrally administered database. Exclusion criteria for this study were: insufficient follow-up (362), lack of baseline 4-year PSA (4YrPSA) (84), NCCN high-risk disease (32), relapse within first 4 years (32). Thus 632 patients were available for analysis. Primary endpoint was disease-free survival (DFS), defined as freedom from clinical, radiological, or PSA progression requiring androgen deprivation therapy. As per Crook et al, per-patient 4YrPSA was categorised as ≤0.2, 0.2 to ≤0.5, 0.5 to ≤1.0, and >1.0ng/ml, and Kaplan-Meier (KM) analysis to 15 years was undertaken for each group. Log-rank test was used to assess failure rate equality between groups (assuming proportional hazards). Starting date for KM analysis was brachytherapy implant date, final date was last follow-up, or failure. Sensitivity and specificity of 4YrPSA as a surrogate for long-term cure was calculated. Results Clinical, disease and follow-up characteristics are summarised in Table 1.

Proportions of patients in each 4YrPSA category were: 63.6% (≤0.2) , 19.3% (0.2 to ≤0.5), 8.7% (0.5 to ≤1.0), and 8.4% (>1.0ng/ml). 10 and 15-year DFS for each category is shown in Figure 1. FIGURE 1: