PO-1986 Early toxicity with stereotactic body radiation therapy for prostate cancer

Purpose or Objective: Stereotactic body radiotherapy (SBRT) has proven to be a new option for localized prostate cancer. SBRT specific indications has been transformed due to SARS-2-COVID19 scenario. This communication shows our data about acute toxicity in patients treated with SBRT during the last sixteen months. Materials and Methods: This retrospective and observational study was performed on prostate cancer patients admitted into our radiotherapy department for SBRT between October 2019 until January 2021. SBRT treatment at our institution has been standardized as an IGRT technique using VMAT radiation therapy due to deliver total doses of 36.25 or 40 Gy in 5 fractions. The following variables were recorded: age, past medical history, previous treatment with anticoagulant or antiplatelet drugs, Performance Status (PS), ACE-27 score, IPSS score, Gleason score, Prostate Volume, Tumor Stage, PSA levels, Risk group following NCCN, Hormonotherapy, Radiation Area, RT Doses as well as different toxicity types depending on Genitourinary (GU) or Gastrointestinal (GI) location. Toxicity review was recorded (after RT, six month and 12 months) according to Common Terminology Criteria for Adverse Events (CTCAE). For the descriptive analysis, analytical variables were represented using absolute and relative frequencies. All statistical analysis were conducted using software from SPSS (version 25.0, Chicago, IL). The hypothesis of our study is SBRT technique will reduce radiotherapy sessions with a low rate of toxicity. Results: A total of 47 patients were included, with a median age of 71 years, performance status 0-1, including high risk prostate cancer (25 patients with Gleason score 6, 17 with score 7, 4 with score 8 and 1 with score 9), all of them without seminal vesicles affected. Related to NCCN risk group, 57.4 % of the patient had very low risk, low risk and favorable intermediate risk and 42.6% were unfavorable intermediate, high and very high risk. Androgen deprivation was associated in 40.4% of the cases with a median of treatment in six months (RI:6-24). Image Guided Radiotherapy was performed by matching of fiducial markers on kvCBCT images that were acquired prior to treatment, for positioning, and during treatment, for intrafraction movement control in 74.5% of the patients. The remaining 25.5% were treated by means of a gating system guided by continuous transperineal ultrasound scanning (Clarity ®system). Acute toxicity grade 1 and 2 after RT was greater at GU (51.1%/21,3%) than GI (12.8%/4.3%) location. During subsequent follow-up no patient developed acute GU or GI toxicity greater than or equal to grade 2. At 6 and 12 months evaluation GU toxicity was greater than GI, 31.7% Vs. 17.1% and 12%Vs.4%, respectively. Conclusion: Evaluation of toxicity during the early phase SBRT has proven to be a well tolerated treatment for prostate cancer in our series.