Background: Docetaxel improves survival in patients (pts) with metastatic hormonosensitive prostate cancer (PC) and castration-resistant prostate cancer. The objective of this phase IIb trial was to assess the activity of low dose docetaxel concurrent with radiotherapy plus standard hormonal treatment in pts with high risk localized CaP. Methods: High-risk localized CaP was defined by ≥ 1 of the following criteria: T3-T4, Gleason score (GS) ≥ 8, PSA > 20 ng/mL, pN+. Pts were randomly assigned to either arm A (LH-RH analogs every 3 months for 3 years and radiotherapy 73.8 Gy [1.8 Gy x 41 fractions] or 74 Gy [2Gy x 37 fractions]) or arm B (LH-RH analogs every 3 months for 3 years, radiotherapy and concurrent weekly docetaxel at 20 mg/m² for 9 weeks). Chemotherapy was started one week before of radiotherapy. Primary endpoint was PSA relapse according to the Phoenix definition. The planned number of pts was 130 to detect a 15% difference with a power of 80% and an alpha of 0.05 (two-sided). Results: From 12/2008 to 9/2012, 130 pts were accrued (Arm A: 64, Arm B: 66). Median age was 68 years (61-73). Patients had T3-T4 (82.6%), GS ≥ 8 (76.3%), PSA > 20 ng/mL (26.9%) and pN+ (18.9%). All characteristics were well-balanced between arms. Median dose of radiotherapy was 74 Gy (72–74.8) in arm A, and 73.8 Gy ( 72-75.6) in arm B. 75.7% of pts received the planned 9 treatments of docetaxel and median number of cycles delivered per patient was 9. After a median follow-up of 29.6 months (9.6-40.2), most common grade 1/2 toxicities (arm A and arm B) were: cystitis ( 12.5% vs 8.3%), diarrhea (35.9% vs 70%), proctitis (12.5% vs 13.3%), rectal tenesmus (3.1% vs 23.3%), asthenia (23.4% vs 61.6%) and dysuria ( 28.1% vs 30.0%). Toxicity G3/G4 diarrhea was reported in 8.3% of pts in arm B and 0% in arm A. G3/G4 lymphopenia occurred less often in arm A than in arm B (3.1% vs 23.3%). %). There was no toxicity-related death. Conclusions: The QRT SOGUG phase IIb trial met its accrual target and shows that concurrent weekly docetaxel can be administered with standard doses of radiotherapy and without increasing toxicity profile. Clinical trial information: 2008-003554-14.