ESTRO 2023 - Abstract Book

S1243

Digital Posters

ESTRO 2023

PO-1530 Prostate SBRT on 1.5T MR-linac or linac-based VMAT: a comparison study from a prospective trial

L. Nicosia 1 , M. Rigo 1 , R. Mazzola 1 , N. Giaj-Levra 1 , E. Pastorello 1 , F. Ricchetti 1 , F. Cuccia 1 , V. Figlia 1 , R. Ruggieri 1 , F. Alongi 1

1 IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Advanced Radiation Oncology Department, Negrar, Italy

Purpose or Objective to compare acute toxicity of prostate cancer (PCa) stereotactic body radiotherapy (SBRT) delivered by MR-guided radiotherapy (MRgRT) with 1.5T MR-linac (MRgRT) or by volumetric modulated arc (VMAT) with linac. Materials and Methods patients with histologically diagnosed low-to-intermediate risk class PCa were treated with exclusive SBRT. The schedule in 5 fractions was 35 Gy for low and intermediate risk class, respectively. Patients treated with MRgRT were enrolled in an ongoing Ethical Committee (EC) approved trial (Prot. n° 23748), while patients treated with CBCT-IGRT linac-based SBRT were enrolled in an EC approved PCa SBRT phase II trial (n° SBRT PROG112CESC). The primary end-point was acute toxicity. Patients were included in the analysis if they had at least 6 months of follow-up for the acute toxicity end-point evaluation. Toxicity assessment was performed according to CTCAE v5.0 scale. International Prostatic Symptoms Score (IPSS) was also performed. Results 137 patients were included in the analysis. 57 (41.6%) were treated with MRgRT, and 80 with conventional linac. The median initial PSA before RT was 6.5 ng/ml (range 1-19). Globally, acute G1, G2, and G3 toxicity occurred in 32 (23.3%) 20 (14.5%), and 4 (2.8%) patients. At the univariate analysis acute G1 did not differs significantly between MRgRT and CBCT-IGRT linac (23.75% versus 21%; p=n.s.), while G2 toxicity was significantly lower in the MRgRT group (4.5% versus 10%; p=0.032). Acute G2 gastrointestinal (GI) toxicity occurred in 7% and 7.5% of MRgRT and CBCT-IGRT linac group (p=0.61), while acute G2 genitourinary (GU) toxicity occurred in 10.5% and 15% of MRgRT and CBCT-IGRT linac group (p=0.004). The median IPSS before and after SBRT was 3 (1-16) and 5 (1-18). Acute G3 toxicity occurred in 2 in the MRgRT and 2 in the linac group (p=n.s.). Conclusion prostate SBRT with 1.5TMR-linac is feasible and safe. Compared to linac-based SBRT, MRgRT seems characterized by a reduced incidence of grade 2 toxicity. A longer follow-up and a larger population is needed to confirm these preliminary data. Purpose or Objective The aim of our study was to evaluate clinical outcomes, toxicity and prognostic factors in patients with prostate cancer underwent surgery and adjuvant or salvage radiotherapy (RT). Materials and Methods From January 2015 to June 2022, 128 patients (pts) underwent salvage or adiuvante RT after radical prostatectomy according to international guidelines. The mean age at the moment of RT treatment was 68 years old (range 38-83) The majority of pts 76,6 % (98 pts) received salvage radiotherapy and remaining 23,4 % (30 pts) were treated with adjuvant intent. All pts were treated in our centre using Versa HD™ or Synergy linear accelerator of Elekta company (Stockholm- Sweden). The volume of RT treatment consisted on prostate bed (70-76 Gy/35-38 fraction based on risk factors; R1, clinical recurrences, PSA) and pelvic irradiation in case of N+ (46 Gy/23 fractions in association of OT with LHRH agonists). Results The mean PSA before RT treatment was 0.8 ng/ml. In 12,5 % of pts RT was prescribed to prostate bed and pelvis and in remaining 87.5 % only to prostate bed. The majority of patients had R1 (70 %) and surgery sequelae before RT treatment (82 %: 72.7 % erectile dysfunction plus urinary disorders and 9.3 % urinary disorders). After a median follow-up of 4 years (range 4 – 92 months) overall survival (OS) and cancer specific survival (CSS) rates were 93 % and 99 % (only 1 pt died due to PD). Moreover, the biochemical progression free survival (bPFS), and clinical progression free survival (cPFS) resulted 66 % and 78 %, respectively. Finally, we did not observe any recurrence at prostate tumor bed irradiated. At univariate analyses clinical disease before RT treatment, iPSA > 10 ng/ml, pT3a-pT4stage N1, GS ≥ 8, PSA pre-RT treatment > 0,7 ng/ml, PSA nadir > 0,04 ng/ml after RT treatment resulted prognostic factors influencing negatively bPFS and cPFS. At the multivariate analyses GS ≥ 8 and PSA nadir > 0,04 ng/ml after RT treatment were confirmed the main prognostic factors regarding bPFS and GS ≥ 8 cPFS. Due to excellent OS, CSS with lower number of events there was not possible to estimate prognostic factors regarding OS PO-1531 EBRT after radical prostatectomy: outcomes, prognostic factors and toxicity of 128 patients C.P. Soatti 1 , I.C. Fumagalli 2 , D. Delishaj 1 1 asst Lecco, U.O.C. Radioterapia, Lecco, Italy; 2 asst Lecco, U.O.C Radioterapia, Lecco, Italy