ESTRO 2022 - Abstract Book

S504

Abstract book

ESTRO 2022

Purpose: In the present series we report preliminary acute and late toxicity of the first 100 patients who received 1.5T MR-guided daily-adaptive stereotactic body radiotherapy for prostate cancer.

Materials and Methods Methods: We report the outcomes of the first 100 patients treated from October 2019 to December 2020. All the patients were enrolled in a prospective study (MR Linac n°XXXX). Before the treatment, the insertion of the rectal spacer was proposed as optional and applied in 37 patients. Hormone therapy was prescribed according to international guidelines in 32 patients. Toxicity was prospectively collected and assessed using Common Terminology Criteria for Adverse Events (CTCAE v5.0). Quality of life was assessed using IPSS, ICIQ-SF, IIEF-5, EORTC QLQ-C30, QLQ-PR25 and EPIC-26 questionnaires. Results Results: A total of 100 patients were treated: 34 were low risk, 29 were favorable intermediate-risk, 31 were unfavorable intermediate-risk, 2 high risk, 4 were low-volume M1 patients. The median age was 71 years (range, 52-84 years), median IPSS was 3 (range, 0-7); SBRT was delivered using 1.5T MR-guided daily adaptive radiotherapy in 5 sessions for a median total dose of 35 Gy (35-36.25 Gy) on consecutive (n=75) or alternate days (n=25). The adapt-to-shape workflow was mainly adopted (480/500 sessions). The median treatment time was 40 minutes (range, 33-83 minutes). The median PTV volume was 105.8 cc (range, 13.98-196.4cc). Acute toxicity rates were as follows: 5 acute G2 genitourinary tract pain events, and two cases of urethral stenosis requiring catheterization fully resolved within the first follow-up. For gastrointestinal toxicity, only 4 cases of G2 events (rectal tenesmus or proctitis) were observed. All the G ≥ 2 events occurred after an average time of 30 days from the end of RT. With a median follow-up of 12 months (range, 3-20 months), for late events, we have recorded 3 late G2 GU events (urinary tract pain) and one G3 GU event for a patient who received a TURP 8 months after radiotherapy. For late GI events, we have recorded 3 G ≥ 2 GI proctitis, including one patient treated with argon laser for radiation-induced proctitis. All patients are alive and in disease control except for one M1-low volume patient who developed distant progression two months after RT. Preliminary QoL assessment revealed a transient decline in fatigue, fully recovered after first follow-up. Conclusion Conclusions : Our preliminary report on the first 100 patients of patients who received 1.5T MR-guided daily-adaptive SBRT for prostate cancer reports excellent results in terms of acute toxicity, and minimal impact on QoL. More mature data are warranted. A. Montero 1 , O. Hernando 1 , X. Chen-Zhao 1 , J. Valero 1 , A. Prado 2 , E. Sanchez 1 , M. Lopez 1 , R. Ciervide 1 , M. Garcia-Aranda 3 , B. Alvarez 1 , M. de la Casa 2 , R. Alonso 1 , P. Fernandez-Leton 2 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Medical Physics, Madrid, Spain; 3 HM hospitales, Radiation Oncology, Madrid, Spain Purpose or Objective To evaluate tolerance and feasibility of an ultra-hypofractionated urethra-sparing SBRT schedule after radical prostatectomy Materials and Methods From April-2019/September-2021, 51p with median age of 68-yo (55-80) were prospectively included. Patients’ characteristics are detailed in table 1. Adjuvant radiotherapy (ART) in 16p (31%) and salvage radiotherapy (SRT) in 35p (69%); median time from surgery to ART 4.5 months (1-9) vs. 17 months (7-213) to SRT. All patients underwent VMAT 36.25Gy in 5 fractions of 7.25Gy on every-other-day to surgical bed (RTOG guidelines). Urethra-sparing protocol reduced prescribed dose/fraction to urethra and surrounding zone from 7.25Gy to 6.5Gy; 13p (25.5%) underwent elective nodal pelvic irradiation with 26Gy in 5 fractions of 5.2Gy and 5p with macroscopical pelvic nodal disease received simultaneous integrated boost at a dose of 40Gy in 5 fractions of 8 Gy. Thirty-two (63%) were treated in a Novalis-Linac with daily ExacTrac-IGRT based upon prostate-bed gold-fiducial markers, whereas 19p (37%) were treated in a Versa-HD-Linac with Clarity-4D-Monitoring-IGRT-system. Daily immobilizationwith endorectal balloon filled-up with 80cc air to minimize rectal movements was used. All patients received alpha-1-receptor antagonists before, during and up to one month after completing SBRT; 13p (25.5%) received androgenic deprivation therapy (ADT) for a median time of 24 months (range 6-24). We reported results of biochemical progression-free survival (bPFS) defined according to ARTISTC criteria (PSA ≥ 0.4 ng/mL and rising after completion postoperative SBRT); clinical progression-free survival (cPFS) defined as no evidence of local or metastatic progression excluding evidence of biochemical recurrence and distant metastases free-survival (DMFS PD-0576 Ultra-hypofractionated SBRT following radical prostatectomy: first results of a phase II trial