ESTRO 2021 Abstract Book

S1094

ESTRO 2021

the pattern of progression and local control after aRT. Results

Between 2014 and 2018, 63 patients had aRT of 89 MET (68 lymph node (ln-) MET and 21 bone (OSS-) MET). The mean volumes of GTV and PTV were 2.2 ml and 15 ml. The 50 Gy scheme was used in 34 MET and 55 MET were treated with SABR. The median follow-up time was 36.6 months. Local progression occurred in 7 MET, resulting in a local control of >90 % after 3 years. Patients with OSS MET and with a larger (than mean) PTV were at higher risk of local progression (log-rank test: p < 0,001 and p = 0,01, respectively, see figure). Regional progression adjacent to the irradiated area was observed in 16 of 46 patients with at least one Ln-MET (51% free of regional progression @3y). In 34 patients (54%), a distant progression was reported. Median time to detection of other progressive lesions was 24 months. 13 patients (21%) had another aRT.

Conclusion Local ablative radiotherapy in patients with PSMA-PET staged oligometastatic prostate cancer can achieve high rates of local control, but regional or distant progression is common. Further studies are warranted, e.g. to define optimal target volume coverage. PO-1333 Efficacy of stereotactic radiation therapy for the treatment of nodal oligorecurrent prostate cancer S. Cozzi 1 , L. Bardoscia 1 , D.S. Solla 1 , G. Timon 1 , A. Botti 2 , B. Gladys 1 , F. Vigo 1 , P. Ciammella 1 , C. Iotti 1 1 Radiation therapy Unit, Azienda USL - IRCCS di Reggio Emilia, Reggio Emilia, Italy; 2 Medical Physics Unit, Azienda USL - IRCCS di Reggio Emilia, Reggio Emilia, Italy Purpose or Objective The purpose of the present study is to evaluate the efficacy and safety of involved-nodal stereotactic radiotherapy (SBRT) for the treatment of nodal oligorecurrence of prostate cancer (oligo-rPC). Materials and Methods Patients (pts) with pelvic nodal oligo-rPC (1 to 3 lesions) following primary surgery, radical radiotherapy or salvage radiotherapy undergoing involved nodal SBRT with biological effective dose (BED3) > 100 Gy, with or