ESTRO 2022 - Abstract Book

S503

Abstract book

ESTRO 2022

To assess the impact of metformin on biochemical failure (BF) in localized prostate cancers (PC) treated with radical prostatectomy (RP) or radiation therapy (RT).

Materials and Methods 1,449 patients undergoing RP (n=1338, 92.3%) or RT (n=108, 7.5%) for localized PC at two institutions between July 2007 and January 2020 were evaluated for metformin use, demographic/oncologic characteristics, and biochemical outcomes. Androgen deprivation therapy was utilized per NCCN guidelines. BF rates were assessed overall and at 1, 3, and 5 years. Time to BF was estimated via Kaplan-Meier; logistic regression and Cox proportionate hazards models were generated to adjust for significant differences. Results Of 1,449 patients, 148 (10.2%) utilized metformin at time of diagnosis, while 1,301 (89.8%) did not. Patients on metformin were significantly older, had higher body mass indexes (BMI), and more aggressive disease (Gleason score (GS)>7). Kaplan- Meier analysis at a mean ± SD follow-up of 3.6±2.6 years suggested that patients on metformin were less likely to experience BF at later timepoints (Tarone-Ware X2 =0.088); however, univariate analysis showed no differences in BF at 1, 3, and 5 years following treatment. After adjusting for age, BMI, preoperative PSA, and GS in multivariate analysis, patients on metformin were significantly less likely to experience BF at 5 years and overall timepoints in both treatment groups. Similarly, in Cox regression, metformin use was independently associated with a 40% relative risk reduction in BF compared to those not on metformin. Conclusion Metformin use was associated with increased age, higher BMI, and more aggressive PC. In multivariate analysis, metformin use was associated with a significant risk reduction in BF overall and at 5 years following primary treatment; this trend was not witnessed in univariate analysis. These results suggest the need for future investigations of metformin’s role in disease- free survival in men with localized PC. 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 were 35 Gy and 36.25 Gy for low and intermediate risk class, respectively. Patients treated with MRgRT were enrolled in an ongoing Ethical Committee (EC) approved trial (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. PD-0574 1.5T MR-guided RT versus linac-based VMAT SBRT in localized prostate cancer: a toxicity comparison L. Nicosia 1 , C. Vitale 1 , F. Cuccia 1 , M. Rigo 1 , V. Figlia 1 , R. Mazzola 1 , N. Giaj-Levra 1 , F. Ricchetti 1 , R. Ruggeri 1 , F. Alongi 1 1 IRCCS Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar, Italy

PD-0575 Toxicity and QoL report of 1.5T MR-guided SBRT for prostate cancer in the first 100 patients

F. Cuccia 1 , V. Figlia 1 , M. Rigo 1 , L. Nicosia 1 , R. Mazzola 1 , N. Giaj-Levra 1 , F. Ricchetti 1 , G. Attinà 1 , E. Pastorello 1 , C. Vitale 1 , A. De Simone 1 , D. Gurrera 1 , S. Naccarato 1 , G. Sicignano 1 , R. Ruggieri 1 , F. Alongi 1

1 IRCCS Sacro Cuore Don Calabria, Advanced Radiation Oncology Department, Negrar di Valpolicella, Italy

Purpose or Objective