ESTRO 2023 - Abstract Book

S1214

Digital Posters

ESTRO 2023

1 Hospital de Braga, Radiation Oncology, Braga, Portugal; 2 Hospital de Braga , Radiation Oncology, Braga, Portugal; 3 Júlio Teixeira SA - Instituto CUF , Radiation Oncology, Porto, Portugal Purpose or Objective To characterize the effect of a prostate-rectum spacer on dose to neurovascular bundle (NVB) during external beam radiation therapy (EBRT). Dose to rectum was also evaluated. Materials and Methods In February 2022, ten consecutive patients with histologically confirmed prostate adenocarcinoma, were enrolled into a prospective study at our institution, with the following inclusion criteria: age >= 18 years, clinical stage of T1c-2, Karnofsky Performance Status > 70, with any NCCN risk group. Initially, the patients underwent a baseline CT scan. Then, they were injected with perirectal hyaluronic acid (HA) spacer and rescanned with CT and MRI. 3D-CRT plans were created on both scans (pre-spacer and post-spacer) for dosimetric comparison of NVB. The dose prescribed to prostate was 76Gy in 38 fractions. The comparison of dosimetric parameters was performed using the Paired-sample T Test and Wilcoxon Test, using the IBM SPSS Statistics version 26 software. Results The population included males with a mean age of 72 (±2.56) years, presenting with a mean PSA 8.51 (±7.56) ng/mL. All patients underwent androgen deprivation therapy (ADT). The mean prostate volume (PV) was 34.3 cc (21-66, ±13.36). Neurovascular bundle dosimetry Non - hyaluronic acid spacer plans Hyaluronic acid spacer plans P value Mean dose (Gy, DP) 71.59 ±2.44 68.37 ±4.17 0.004 Maximum dose (Gy, DP) 79.45 ±0.51 78.75 ±0.73 0.002 V60Gy (%) 88.21 ±9.30 82.73 ±15.14 0.06 V70Gy (%) 71.06 ±11.13 57.38 ±14.33 0.002 Rectum dosimetry Non - hyaluronic acid spacer plans Hyaluronic acid spacer plans P value V60Gy (%) 25.73 ± 6.60 13.62 ± 4.51 0.005 V70Gy (%) 11.10 ± 5.43 2.67 ± 1.82 0.005 V75Gy (%) 5.09 ±3.82 0.20 ±0.23 0.008 The PV does not correlate significantly with the mean dose (p=0.361), maximum (p=0.071), V60 (p=0.669) and V70 (p=0.064) to NVB after placing the HA. In all, 40% of patients (4/10) developed acute Grade 1 GI toxicities. No patients had acute Grade ≥ 2 GI toxicities. None of the patients reported any rectal bleeding. There were no reports of any adverse events including rectal perforation, or infection after HA injection. 8 patients (80%) had erectile disfunction (ED) at baseline. During the follow-up (3 months after treatment) all patients had ED (EPIC). Conclusion Injection of HA was able to achieve a reduction of irradiated NVB dose volumes irrespective of PV. It reduced the V70 Gy, mean and maximum doses in the NVB, which potentially might decrease sexual impairment. However, it was not possible to associate the use of the spacer with sexual toxicity, since all patients were under ADT. Injection of HA also significantly reduced rectum V60, V70 and V75. In a future analysis we will evaluate ED using EPIC after resuming ADT and correlate it with dose to NVB. The presenting study proves that injection of HA reduces significantly the dose to NVB with 3DRT, however we believe differences will be greater when using IMRT or SBRT, and we look forward to present it in a future work. G.C. Iorio 1 , D. Bongiovanni 1 , I. Bonavero 1 , G. Petruzzellis 1 , S. Bartoncini 1 , E. Gallio 2 , V. Chiofalo 1 , E.M. Cuffini 1 , C. Grossi 1 , M. Levis 1 , U. Ricardi 1 1 University of Turin, Department of Oncology, Turin, Italy; 2 University of Turin, Department of Medical Physics, Turin, Italy Purpose or Objective extreme hypofractionation is gradually becoming a mainstay of treatment for prostate cancer (PCa). Patients’ (pts) tolerance to such RT regimes is undoubtedly under the spotlight. Herein, we report acute toxicity data and predictors in a single-center observational analysis. Materials and Methods this toxicity analysis pertains to a consecutive series of low-to-high-risk PCa pts treated with (LINAC-based VMAT) extreme hypofractionation (42.7Gy/7 non-consecutive fractions-frs, 15-19 days) +/- ADT. Genitourinary (GU) and gastrointestinal (GI) acute toxicities were scored according to RTOG during the following timepoints: each RT fr, 1- and 3-months (mos) from RT end. Patient (risk-group, previous TURP, prostate cc ≤ or > 80cc, IPSS score ≤ or > 12), treatment (neoadjuvant concomitant-adjuvant ADT use, overall treatment time-OTT ≤ 17 or >17 days) and dosimetric (V37Gy bladder ≤ 10cc, ≤ 15cc, ≤ 20cc, >20cc) variables were analyzed (logistic regression analysis) to investigate potential acute RTOG GU G2+ toxicity predictive/protective factors. Results 187 pts (mean age 74.5 years) were treated between May 2020 and October 2021. Most pts were classified as intermediated risk (77.5%), followed by high-risk (18.2%) and low-risk (4.3%). ADT was administered to 56.1%. Baseline IPSS >12 was observed in 23.9%. Most pts had a prostate volume<80cc (83.9%). Previous TURP was reported for 38 pts, mainly more than 2 years before RT (31 pts). The most commonly recorded V37Gy bladder metric was 16-20cc(57.2%), followed by 11- PO-1496 Acute toxicity rates and predictors in extreme hypofractionation for localized prostate cancer