ESTRO 2021 Abstract Book

S1145

ESTRO 2021

Conclusion SBRT for LN oligorecurrence from PC provides optimal LC and high tolerability. However, its effect on disease progression is still unclear as well as which pts are more suitable for this approach.

PO-1395 Post-prostatectomy ultra-hypofractionated SBRT: preliminary results of a phase II trial A. Montero 1 , O. Hernando 1 , J. Valero 1 , X. Chen-Zhao 1 , J. Marti 2 , A. Prado 2 , E. Sanchez 1 , M. Lopez 1 , R. Ciervide 1 , M. Garcia-Aranda 1 , B. Alvarez 1 , R. Alonso 1 , P. Garcia 2 , M. Nuñez 1 , J. Palma 1 , M. Izquierdo 1 , K. Rossi 1 , C. Cañadillas 1 , P. Fernandez-Leton 2 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Medical Physics, Madrid, Spain Purpose or Objective To evaluate feasibility and tolerance of ultra-hypofractionated urethra-sparing SBRT in a cohort of prostate cancer patients after radical prostatectomy Materials and Methods From April 2019 to February 2021, 40p with a median age of 68-yo (55-80) were include in this prospective phase II trial. Patients’ characteristics before enrollment are detailed in Table 1. Adjuvant radiotherapy (ART) was considered in 10p (25%) andsalvage radiotherapy (SRT) in 30p (75%); median time from surgery to SBRT: 20 months (2-211) (4.5 months (2-8) to ART vs. 31.5 months (7-211) to SRT). All patients underwent VMAT up to a total dose of 36.25Gy in 5 fractions of 7.25Gy on every-other-day to the surgical bed (RTOG consensus guidelines, Fig.1). Our urethra-sparing protocol reduced prescribed dose per fraction to the urethra and the surrounding transitional zone from 7.25 Gy to 6.5 Gy; 10p (25%) underwent elective nodal pelvic irradiation up to a total dose of 25 Gy in 5 fractions and 3p (7.5%) with macroscopical pelvic nodal disease received simultaneous integrated boost up to 40 Gy in 5 fractions. Twenty-eight patients (70%) were treated in a Novalis Linac with daily ExacTrac systemIGRT based upon prostate bed gold-fiducial markers whereas 12p (30%) were treated in a Versa-HD Linac with Clarity-4D Monitoring IGRT system. In every fraction, daily immobilization with an endorectal balloon filled-up with 80cc air to minimize rectal movements was used. Dose constraints used are detailed in table 1. Patients were pre-medicated with alpha-1 receptor antagonist before, during and up to one month after completing SBRT. Eight patients (20%) received androgenic deprivation therapy (ADT).