ESTRO 2021 Abstract Book

S1114

ESTRO 2021

Conclusion We have validated our new critical organ constraints regarding acute toxicity in terms of isotoxicity. Acute GU toxicity appears earlier in HF group but recovers faster, without differences in grade but with a higher G2 tendency in the CF group. GI acute toxicity has been mild with no differences between arms. PO-1357 LDR-Brachytherapy vs SBRT: PSA kinetics and toxicity outcomes in localized prostate carcinoma M. Cerrolaza 1 , A. Mendez 2 , M.D.M. Puertas 2 , C. García 2 , S. Flamarique 2 , C. Escuin 1 , V. Navarro 1 , A. Lanuza 2 , D. Villa 3 , B. Garcia 2 , M. Tejedor 2 1 University Hospital Miguel Servet, Radiation Oncology, Zaragoza, Spain; 2 University Hospital Miguel Servet , Radiation Oncology, Zaragoza, Spain; 3 University Hospital Miguel Servet , Medical Physics, Zaragoza, Spain Purpose or Objective Localized Prostate cancer has multiple therapeutic options including radical prostatectomy, brachytherapy and external beam radiation therapy. In our center the radiotherapy techniques used for this type of cancer are LDR-brachytherapy (BQT) and stereotactic body radiation therapy (SBRT). Our objective is to identify and compare the oncologic results, toxicities, and PSA response in the treatment of localized prostate cancer by LDR brachytherapy and SBRT. Materials and Methods Data were retrospectively collected for all patients diagnosed with low or intermediate-risk prostate cancer treated with LDR brachytherapy or SBRT from 2015 to 2016. BQT was performed by transperineal insertion of permanent seeds of Iodine 125. The prescribed dose of SBRT was 35 Gy in 5 fractions of 7 Gy once a week. Oncologic characteristics and follow-up were evaluated every 6 months including PSA, toxicities (CTCAE V5) and recurrences. A comparative analysis was performed using chi-square and T student. A p-value less than 0.05 was statistically significant. Results 146 patients were analyzed, 66 treated with BQT (45%) and 80 SBRT (55%). The mean age was 67.8 in the BQT group and 70.26 in the SBRT group (p=0.036) with a PSA at diagnosis of 7.31 in the BQT group and 9.055 in the SBRT group (p=0.004). The most common Gleason grade in both groups was 6, 85% in BQT and 60% SBRT (p=0.001). The most frequent stage was T1c, 97% treated with BQT and 75% with SBRT (p=0.002). Prior to radiotherapy treatment, 17% of patients who underwent BQT and 44% SBRT, received hormone blockade (CAB) (p= 0.001). Differences were observed in acute intestinal toxicity with greater toxicity in those treated with SBRT. When evaluating chronic toxicity, differences were observed in greater urinary toxicity in patients treated with BQT and greater intestinal toxicity in patients treated with SBRT. Throughout follow-up 17 patients (25.75%) presented grade 3 toxicity with BQT and 5 patients treated with SBRT (6.25%). PSA follow-up was studied in subjects who had not previously received CAB. They presented differences in the