ESTRO 37 Abstract book

S869

ESTRO 37

EP-1612 Pre-treatment and prognostic value in intermediate risk localized prostate cancer D. Büchser 1 , A. Gómez-Iturriaga 1 , F. Casquero 1 , A. Urresola 2 , A. Ezquerro 2 , J. Cacicedo 1 , I. San Miguel 1 , F. Suarez 1 , P. Bilbao 1 1 Hospital Universitario Cruces, Radiation Oncology, Barakaldo, Spain 2 Hospital Universitario Cruces, Radiology, Barakaldo, Spain Purpose or Objective Intermediate-risk prostate cancer represents the largest of the risk groups and is comprised of a heterogeneous population of patients with variable prognoses. This heterogeneity presents a challenge to both physicians developing treatment recommendations and patients who ultimately choose a specific treatment approach. The purpose of this study was o prospectively evaluate multiparametric MRI (mpMRI) staging accuracy as an independent predictor of outcome as compare to traditional clinical variable in patients treated with high- dose-rate (HDR) brachytherapy (BT) and external beam radiotherapy (EBRT) for intermediate-risk localized prostate cancer. Material and Methods In September 2010 we launched a prospective study of mpMRI guided HDR-BT (15Gy) and supplemental EBRT (37.5Gy) for intermediate and high-risk prostate cancer. The primary endpoints were biochemical (nadir +2ng/mL) and metastatic failure. Clinical variables included baseline PSA value, clinical T- stage, Gleason score, percentage of positive cores on prostate biopsy, use of hormonal therapy, MRI T-stage, risk-group based on clinical T-stage and risk-group based on MRI T-stage. We specifically analyzed the intermediate-risk subgroup (NCCN classification) according to classical clinical variables (PSA, clinical T stage prior to mpMRI and Gleason score) so as to assess the impact of extracapsular extension or seminal vesicle invasion (i.e T3) on outcomes. Cumulative hazard rate function was estimated through the Nelson-Aalen method in order to describe the cumulative risk of the events of interest. Univariate and multivariate hazard ratios were obtained from proportional hazards Cox regression models. Log rank tests were used to compare hazards across categories of MRI-based T stages. Results Eighty-one patients were prospectively treated, median age was 71 years (range 56-82); Thirty-nine percent were Gleason 6, 36 % Gleason 7 (3+4) and 25% Gleason 7 (4+3); median baseline PSA was 8 ng/mL (1.9-19 ng/mL). Median follow-up was 45 months (range 20-81). At the time of the current analysis, 6 (7.4%) patients had a biochemical failure and 2 (3.7%) had developed distant metastases. The 5-year cumulative risk of biochemical failure for patients with MRI-T1/T2 stage and MRI-T3 stage were 0% and 18% respectively (p=0.002). The 5-year cumulative risk of metastatic failure was 0% and 8% respectively (p=0.018). None of the traditional variables (Primary pattern of Gleason score, PSA or clinical T-stage) predicted for clinical outcomes. The only independent predictors of biochemical and metastatic failure ware the presence of extraprostatic extension on mpMRI and the percentage of positive cores on biopsy. mpMRI accuracy

patients without an IRS was 77.2% [39.2-91.4], and the placement of an IRS resulted in an increased median TCP of 96.3% [80.8-99.2]. The median TCP of the V-IRS was 96.3% [80.8-99.7], showing that the V-IRS has the potential to accurately predict the TCP resulting from a real IRS (Figure 2). If the same patients were heterogeneous for the SNP’s for rectal toxicity, the median TCP without IRS would be 48.9% [15.9-72.3], but with IRS this increases to 92.9% [61.6-99.1] without exceeding the 5% NTCP threshold.

Figure 1 - TCP: Tumor control probability; NTCP: Normal Tissue Complication Probability; IRS: implantable rectum spacer; nf: number of fractions

Figure 2 - IRS: implantable rectum spacer; TCP: tumor control probability; NTCP: normal tissue complication

probability Conclusion

In this study we showed that placing an IRS can potentially improve the outcome for prostate cancer patients when combined with dose escalation. Additionally, results suggested that the placement of an IRS could improve radiotherapy outcome in patients heterogeneous for SNP’s correlated with rectum toxicity. We concluded that the developed model together with a V-IRS has potential to serve as a multifactorial decision support system for the placement of an IRS.