ESTRO 2025 - Abstract Book

S2137

Clinical - Urology

ESTRO 2025

4476

Digital Poster Early Complications, Quality Distribution and Dosimetric Impact of Hyaluronic Rectal Spacer for Prostate Cancer Stereotactic Body Radiation Therapy Marco Galaverni 1 , Federico Colombo 1 , Claudia Grondelli 1 , Francesco Salaroli 1 , Cristina Dell'Anna 1 , Ilaria Renna 1 , Maria Luisa Bergamini 1 , Giovanni Ceccon 1 , Elisabetta Lattanzi 1 , Stella Gianni 1 , Umberto Maestroni 2 , Francesco Ziglioli 2 , Davide Campobasso 3 , Carmelinda Manna 4 , Ruffini Livia 5 , Caterina Ghetti 6 , Giovanna Benecchi 6 , Michele Maddalo 6 , Nunziata D'Abbiero 1 , Nicola Simoni 1 1 Radiation Oncology Unit, University Hospital of Parma, Parma, Italy. 2 Department of Surgery, University Hospital of Parma, Parma, Italy. 3 Urology Unit, University Hospital of Parma, Parma, Italy. 4 Unit of Diagnostic and Interventional Radiology, University Hospital of Parma, Parma, Italy. 5 Nuclear Medicine Division, University Hospital of Parma, Parma, Italy. 6 Medical Physics Unit, University Hospital of Parma, Parma, Italy Purpose/Objective: To assess post-injection complications, implant quality distribution, and impact on rectal dose of hydrogel rectal spacer (RS) for patient with prostate cancer (PCa) treated with Stereotactic Body Radiation Therapy (SBRT). Material/Methods: Patients with localized PCa who had undergone hydrogel spacer placement at our Institution were included in this retrospective study. Early procedure complications were recorded. Hydrogel quality distribution using Spacer Quality Score (SQS), Symmetry Score (SYM), and rectal wall infiltration (RWI) were assessed on post-implant T2 weighted magnetic resonance (MR). Associations with rectal dosimetry and toxicity were evaluated. Results: From January 2022 to June 2024, 70 patients (median age 76 years) with localized PCa received RS implant prior to SBRT. Overall, the procedure was well tolerated, with 22 (31.4%) G1 and 6 (8.6%) G2 cases of post-injection adverse events according to Manufacturer and User Facility Device Experience (MAUDE) classification. A RWI was identified on MR in 23 (32.9%) patients, as score 1 (“rectal wall edema/signal changes, without infiltration”), 2 (“partial infiltration”), and 3 (“full - thickness infiltration”) in 2.9%, 27.1%, and 2.9%, respectively (figure 1).

Intraprostatic injection of RS was observed in 4 (5.7%) patients, without significant sequelae reported. Five (7.1%) patients, due to RWI score 3 or intraprostatic RS, received radiotherapy upon spacer reabsorption, and were excluded from subsequent analysis. For the 65 patients analyzed, Planning Target Volume (PTV) dose prescription was 36.25 Gy/5 fraction in 17 (26.2%) patients, with a concomitant boost to the prostate ≥ 40 Gy in the remaining 48 (73.8%). SQS score was defined as 0 (“inadequate”), 1 (“good”), and 2 (“excellent”) in 3 (4.6%), 42 (64.6%), and 20 (30.8%) patients, respectively. SQS score was associated with rectal D max (p = 0.000), maximum dose to 1 cc (p = 0.000), V36 (p = 0.003), V30 (p = 0.000), and V18 (p = 0.008). SYM score was 1 (“best”), 2, 3, 4, and 5 (“worst”) in 45