ESTRO 2021 Abstract Book

S639

ESTRO 2021

to anatomical changes.

Conclusion Mean diffusivity may detect RT induced microstructural damage of WM and GM in LGG patients. Further validation on a larger patient population and assessment of the clinical relevance is ongoing.

Poster discussions: Poster discussion 14: Prostate 2

PD-0806 HDR-BT + SBRT for prostate cancer. QoL and toxicity analysis in a prospective phase II trial. D. Büchser 1 , A. Bilbal 2 , E. Mayrata 1 , F. Perez 1 , J.M. Espinosa 1 , I. Valverde 1 , B. Santos 3 , F. Casquero 1 , A. Gomez- Iturriaga 1 1 Hospital Universitario Cruces-Biocruces Health Research Institute, Radiation Oncology, Barakaldo, Spain; 2 Hospital Universitario Cruces, Radiation Oncology, Barakaldo, Spain; 3 Biocruces Health Research Institute, Epidemiology and statistics, Barakaldo, Spain Purpose or Objective To report toxicity and impact on QoL in patients treated with a combination of HDR prostate brachytherapy and prostate SBRT for intermediate and high-risk prostate cancer in a phase II prospective trial. Materials and Methods A total of 52 patients were recruited in an institutional review board-approved prospective phase II trial of the combination of HDR-BT real-time 15 Gy followed by SBRT to the prostate: 5 fractions of 5 Gy each delivered in consecutive days. Image-guided RT through intrafraction fiducial marker monitoring was used for SBRT. Eligible patients had histologically confirmed intermediate (IR), high (HR) or very-high (VHR) risk prostate adenocarcinoma according to NCCN stratification. All patients underwent a diagnostic mpMRI of the prostate unless clinically contraindicated. Androgen deprivation therapy was administered according to risk stratification: 12 months for HR and VHR. Genito-urinary (GU) and gastro-intestinal (GI) toxicity was assessed according to CTCAE v5. Patient QoL was evaluated through ICHOM (international consortium for health outcomes measurement) methodology with EPIC and EORTC QLQ-PR25 questionnaires. A decreased of > 0.5 standard deviation of baseline values was considered clinically relevant. Results Fifty-one patients had completed treatment at the time of the current analysis with a median follow-up of 10 months, 34.6% favorable IR, 17.3 unfavorable IR, 34.6% HR and 13.5% VHR. Median age was 75 years and median baseline IPSS was 4 (0-19). Median PSA before treatment was 7.1 ng/mL (3,8-110 ng/mL) and median volume of the prostate was 33 cc (16-70 cc). Short-term androgen deprivation therapy (ADT) was administered to 21.2% of patients whereas 42% received long-term ADT, the rest of the patients did not receive hormonal therapy. No severe (i.e. G3-4) acute or late events were recorded. The cumulative incidence of acute G2 GU and GI events were 17.3% and 3.8% respectively. The most common acute GU symptom was dysuria whereas the most common acute GI event was proctitis. Thirty-seven patients reached a follow-up > 6 months and were eligible for chronic toxicity analysis. Among these, the cumulative incidence of late G2 GU events was 10.8%, no G2