ESTRO 2020 Abstract Book

S608 ESTRO 2020

Results When using the mDSS, 736 (49%) patients were expected to obtain more QALYs with RT, and 764 (51%) with RP. In the base case, the mDSS is estimated to result in lower costs (-€708, CI: -€892- -€524) and more QALYs (0.075 years, CI: -1.353-1.504 years) than randomized treatment selection (Figure 2). The probability that the mDSS is cost- effective is estimated to be 95.2%, when using a willingness to pay threshold of €80,000 per QALY, in accordance with Dutch guidelines. The mDSS was dominant (increase in QALYs and decrease in costs) in 93.8% of the simulations.

(most to a total dose of 45Gy). Outcome analysis was performed in 264 patients, with a median follow-up of 35.6 months. Median pre-sRT PSA was 0.59ng/mL (IQR-0.763; 54.4% had >0.5ng/mL). Undetectable values were subsequently measured in 75 patients (28.4%), a median of 11.2 months after sRT (IQR-14.0). The group of patients who achieved undetectable PSA had a significantly shorter time from biochemical recurrence to sRT (6.6 versus 10.5 months in the detectable PSA group, p=0.025) and a lower rate of pre-sRT PSA >0.5ng/mL (37.3% versus 61.4% patients, p<0.001). There was also a higher rate of HT during sRT (9.3% versus 2.6%, p=0.042). All other relevant variables were balanced between the groups. Five patients in the undetectable PSA group later suffered a biochemical recurrence (6.7%), and two had a clinical recurrence (2.7%, distant). After undetectable PSA, a statistical significant improval was noted in BC-RFS, C-RFS, HT-FS and OS on univariate analysis (UVA). After multivariate analysis (MVA), the same effect was still observed in BC-RFS (92.8 versus 48.4% at 3 years; HR 0.135, CI95% 0.053-0.343, p<0.001 on MVA), C-RFS (98.0 versus 74.4% at 3 years; HR 0.106, CI95% 0.026-0.441, p=0.002 on MVA) and HT-FS (100 versus 71.5% at 3 years; HR 0.055, CI95% 0.007-0.406, p=0.004 on MVA). There was no significant effect on OS (possibly due to a low number of events - 100 versus 95.2% at 3 years, p=0.043 on UVA). Conclusion The achieval of undetectable PSA after sRT seems to be a predictor of less frequent biochemical and clinical recurrence. Hormone therapy-free survival and overall survival are also higher. An early sRT strategy (as soon as biochemical recurrence is diagnosed after radical prostatectomy, if possible before PSA reaches 0.5ng/mL), as currently recommended, could maximize the probability of undetectable PSA after sRT, and as such improve prognosis. PO-1156 The role of magnetic resonance imaging in prostate cancer E. González Del Portillo 1 , C. Gil Restrepo 1 , P. Soria Carreras 1 , M. Martín Izquierdo 2 , Á. Virseda Rodríguez 3 , J. García García 3 , F. Gómez Veiga 3 , L.A. Pérez Romasanta 1 1 Complejo Asistencial Universitario de Salamanca, Radiation Oncology, Salamanca, Spain ; 2 Complejo Asistencial Universitario de Salamanca, Radiology, Salamanca, Spain ; 3 Complejo Asistencial Universitario de Salamanca, Urology, Salamanca, Spain Purpose or Objective The local staging of prostate cancer (PC) is based on digital rectal examination (DRE) and conventional imaging strategies such as transrectal ultrasound (TUS) or computed tomography (CT). Today, multiparametric magnetic resonance imaging (mMRI) is increasingly used in order to improve tumor detection, local staging, prostate biopsy guidance and radiotherapy planning. Our goal is to assess the local staging (TNM 8th) with mMRI (SMRI) in comparison with the local staging achieved by conventional tests (SCT) in a group of patients with local disease. Material and Methods This is a retrospective study from 2017 to 2019. We collected data from 103 patients with localized PC. The SCT was based on DRE completed by a radiation oncologist or an urologist, plus TUS and CT. The SMRI employed MRI. Age, initial PSA (iPSA) and Gleason Score (GS) were registered. Results The median age was 69 years. The most frequent SCT was cT1cN0M0 (63%). In 67 patients we observed a change between SCT and SMRI (65%). The stages by both methods are included in Table 1. Out of the 66 patients with pT1c by SCT, 29% maintained the same stage and 32% changed into T2c by SRMI. Six patients were T2a with SCT and 66.6% did not change this

Figure 2: Cost-effectiveness plane

Conclusion This modelling study shows mDSS based treatment decisions will result in a clinically relevant increase in the patients’ quality of life. Future work should include training predictive models on a single patient dataset for all outcomes, rather than using models from literature, and increasing parameter accuracy to reduce statistical uncertainties. PO-1155 The Impact of Undetectable PSA After Salvage Radiotherapy for Prostate Cancer I. Rodrigues 1 , C. Ferreira 1 , J. Gonçalves 1 , L. Carvalho 1 , J. Oliveira 2 , C. Castro 1 , Â. Oliveira 1 1 Instituto Português de Oncologia do Porto Francisco Gentil, External Radiotherapy Department, Porto, Portugal ; 2 Instituto Português de Oncologia do Porto Francisco Gentil, Urology Department, Porto, Portugal Purpose or Objective To assess the influence of undetectable PSA (<0.01ng/mL) after salvage radiotherapy (sRT) on clinical outcomes, namely biochemical and clinical recurrence-free survival (BC-RFS, C-RFS), hormone therapy-free survival for recurrence after sRT (HT-FS) and overall survival (OS). Material and Methods We performed a retrospective analysis of patients treated with sRT for biochemical/clinical recurrence after radical prostatectomy in our Institution between 2012 and 2017. Statistical analysis was carried using IBM SPSS Statistics 25. Biochemical response was evaluated with PSA, and clinical response was assessed with physical examination, CT, PET- PSMA, PET-choline and/or bone scintigraphy after biochemical recurrence. Results We identified 277 patients who underwent sRT. Median age was 68 years (from 48 to 81). Median time from biochemical recurrence to sRT was 9.6 months (IQR-13.8). Most received 66-70Gy to the prostate bed (78.7%), of which 33.2% underwent a boost to the area of local recurrence and 9.7% also treated the pelvic lymph nodes