ESTRO 2022 - Abstract Book

S1617

Abstract book

ESTRO 2022

Median follow-up period was 79 months (39 – 105 months). One hundred and seventy - seven low risk and sixty - five favorable intermediate risk patients were eligible to BT according NCNN, and fifteen low risk and twenty-five intermediate risk were identified as disapproving as per to EAU . Eight patients were disapproving as per NCCN (unfavorable intermediate risk), but were eligible according to EAU guidelines. Five-year OS, RFS, and DSS were 98.8%, 94.4%, and 100%, respectively. In univariate analysis, the percentage of positive cores on prostate biopsies did not add clinically significant information regarding time to PSA failure after I-125 BT (p=0.793). There was also no relation between disapproving as per EAU guidelines and RFS or DSS (p=0.387; p=0.668 respectively). In Cox multivariate analysis, disapproving as per EAU guidelines was associated with decreased RFS (p=0.014). Conclusion This study demonstrated excellent survival rates, RFS, and DSS of monotherapy iodine-125 brachytherapy and that is an effective treatment for selected cases. Patients who were not eligible according to EAU guidelines demonstrated a lower RFS in Cox multivariate analysis. However, due to the retrospective design of this study, no definite conclusions can be drawn, and future studies are needed to safely assess a possible relationship between these factors. Investigations of such relationships may result in a common criterion that includes all affected men in our societies and more rational treatment of Prostate Cancer.

PO-1816 Dosimetric comparison of intra-operative hyaluronic acid spacer insertion in prostate brachytherapy

S. Brown 1 , S. Worster 1 , V. Currie 1 , J. Nobes 1

1 Norfolk and Norwich University Hospital, Oncology, Norwich, United Kingdom

Purpose or Objective Spacer insertion prior to prostate radiotherapy can improve patient toxicity outcomes through improved sparing of organs at risk without PTV compromise. At our centre, hyaluronic acid spacers are inserted under transrectal ultrasound (TRUS) intra-operatively prior to the insertion of interstitial needles and HDR treatment planning and delivery whilst the patient is under a general anaesthetic. Prior to spacer use at our HDR brachytherapy centre, the CTV would be expanded by 3mm in all but the posterior direction due to the proximity of the rectum to create the PTV (posterior having a 0mm margin). Due to the additional space created by the spacer, we have extended the posterior PTV margin to 3mm to create a 3mm isometric expansion in hope to achieve fewer local recurrences. We present the results of a direct dosimetric comparison of the differences between a no-spacer plan with 0mm posterior PTV margin versus a spacer plan with 3mm isometric PTV margin. Materials and Methods This is a single-centre retrospective review of 10 patients with prostate cancer undergoing an intra-operative hyaluronic acid spacer insertion followed by interstitial needle insertion and TRUS guided HDR brachytherapy boost treatment planning and delivery. For each patient two plans were created to allow dosimetric comparison. The spacer plan (with a 3mm isotropic PTV margin) versus a no-spacer plan (with 0mm posterior PTV margin). The spacer plan was the used plan in each patient’s treatment. Results 10 cases from June 2021 to November 2021 were analysed. Patients had intermediate to high risk prostate cancer and age range 60-77. The average prostate gland size was 47cc. Through spacer insertion, the average prostate-rectal space was 9.1mm when measured at mid-gland in the axial plane on TRUS. TRUS images of pre- and post-spacer insertions were comparable and the presence of a hyaluronic acid spacer did not impede anatomical visualization in any of our 10 cases. We compared dosimetry from the actual plan used (spacer plan with 3mm posterior PTV margin) and non-spacer plan (0mm posterior PTV margin) and found the dosimetry to be as expected. The mean PTV D90% in the spacer plan was 15.83Gy versus 15.47Gy in the no-spacer plan. Likewise, the rectal D2cc was 9.87Gy versus 10.45Gy, the urethral D10% was 16.94Gy versus 16.92Gy and the urethral D30% was 16.4Gy versus 16.4Gy in the spacer versus no-spacer plans. Conclusion In this small review, we have shown that increasing the prostate posterior PTV margin by 3mm in the presence of a spacer is safe and provides similar dosimetry to traditional treatment techniques. We hope this will lead to fewer local relapses in time. We also demonstrate safe and effective intra-operative insertion of hyaluronic acid spacers immediately prior to HDR prostate brachytherapy boost treatment planning and delivery. This enables our patients to have only one invasive procedure allows our department to use its resources more efficiently.

PO-1817 HDR brachytherapy effectiveness in local relapse prostate cancer: 10-year experience

L.O. Rosas Gutierrez 1 , A. Barco Gomez 1 , E. Burillo Nuin 1 , I. Visus Fernandez de Manzanos 1 , M. Barrado Los Arcos 1 , A. Sola Galarza 1 , M. Martinez Fernandez 1 , A.E. Villafranca Iturre 1

1 Hospital Universitario de Navarra, Radiation Oncology, Pamplona, Spain

Purpose or Objective To assess effectiveness of HDR brachytherapy in a series of local relapse prostate cancer patients, through 5-years free- relapse survival and 5-years specific-cause overall survival rates.