2nd ESTRO Forum 2013 S405 Perineural invasion pre-RP: Yes, 11 (6.92%); No, 108 (67.92%) and unknown, 40 (25.16%). Post-RP PSA: < 0.20 ng/ml: 88 (55.34%), ≥ 0.20 ng/ml (Permanently Detectable-PSA or PD-PSA): 55 (34.59%) and unknown: 16 (10.06%). Initial EBRT intention: Adjuvant: 46 (28.93%), Salvage: 113 (71.07%). Corrected EBRT intention: Adjuvant: 23 (14.46%), Salvage: 136 (85.53%), with 23 patients with a PD-PSA (Post-RP PSA > 0.20 ng/ml). Androgenic deprivation: Yes 47 (29.56%), No: 112

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... 4%). Time from BF diagnosis to EBRT referral: Mean: 16.95 months (m), median: 5.50 m, range [0-147 m]. Pre-EBRT PSA: <1 ng/ml: 84 (52.83%), ≥1 ng/ml: 56 (35.22%), unknown: 19 (11.95%). EBRT Dose: 66 Gy: 24 (19.74%), 70 Gy: 79 (59,21%), 72-74 Gy: 45 (21,05%), interrupted: 1 (0,63%). After a median-FU of 23 m, 101 patients (63.52%) remains free of biochemical progression, 16 patients (10.06%) have BP and 42 (26.42%) are lost. Perineural invasion pre-RP is a predictor of poor prognosis after post-RP EBRT (p = 0.012). There is a statistically significant benefit in BFFS when RT dose is >72 Gy (p = 0.048), moreover when patients with PD-PSA are analyzed (p = 0.010). The beneficial effect of increased dose is maintained when pre-EBRT PSA is <1 ng/ml (p = 0.008), but not when pre-EBRT PSA is > 1 ng/ml (p = 0.139). Conclusions: The majority of patients remitted to our Service for EBRT treatment, followed the criteria established for salvagetreatment. Perineural invasion before RT appeared as a bad prognosis factor. Doses over 72 Gy were associated to longer times to BFFS, especially in those patients with PD-PSA. This effect was observed even when PSE pre.EBRT is < 1 ng/ml, but was not observed when that value was > 1 ng/ml. EP-1073 Initial experience with extreme hypofractionation (5.65 Gy x 8 in 3 weeks) in localised prostate cancer Purpose/Objective: Single-institution single-arm prospective study. Endpoint: To assess acute toxicity (to exclude >5% of men have grade 3 GU or any grade 3 GI). Materials and Methods: Since 9-2012 seven NCCN intermediate-high prostate cancer patients were treated with helical tomotherapy. Exclusion criteria: Gleason score ≥8, PSA >20, cT3b-4, IPSS≥20, history of acute urinary retention, difficulty following directions.CTsimulation using Combifix™ with empty rectum and 200 ml bladder filled through urine catheter. CTV included prostate and seminal vesicles. PTV margins were 3-10 mm. Total dose to 95% PTV was 45.2 Gy in 8 fx of 5.65 Gy on alternate days. EQD2= 78.2 Gy (a/b3) or 92.3 Gy (a/b1.5). Rectal constraints: V43 <10%, V40 <15%, V37 <20%, V34 <30%, V28 <40%. MVCT for on-line correction in every fraction. Cleansing enema prior each fraction. Bladder volume during irradiation was controlled through: 1) bladder filling using urine catheter (1 st patient), or 2) measuring urine volume right after every fraction to provide feedback about the delay between water intake and treatment. All men received neoadjuvant-concomitant ADT. Results: Patients characteristics are cT1c-3a, Gleason score 6-7, PSA 8-14 ng/ml.,IPSS 5-8. CTCAE acute GI toxicity: 0/7 grade 2, 2/7 grade 1 (rectal discomfort) and 5/7 grade 0. GU figures: 1/7 grade 2 (dysuria), 4/7 grade 1 (frequency,urgency, nocturia) and 2/7 grade 0. GU grade 2 toxicity was related to catheterisation manoeuvres in the first patient, so that dysuria resolved when bladder volume was controlled measuring urine. For the remaining patients the latter procedure was used. In total, after 56 MVCT, the mean and SD corrections in vertical direction were 0.58±2.4 mm (maximum corrections 4±1 mm). Conclusions: Tomotherapy-delivered extreme hypofractionated radiotherapy in selected prostate cancer patients shows promising early results. Our findings suggest that bladder catheterization should be avoided.