Acute Side Effects After Definitive Stereotactic Body Radiation Therapy (SBRT) for Patients with Clinically Localized Or Locally Advanced Prostate Cancer: a Single Institution Prospective Study

BACKGROUND: The aim of the study was to evaluate acute side effects after extremely hypofractionated intensity-modulated radiotherapy (IMRT) with stereotactic body radiation therapy (SBRT) for definitive treatment of prostate cancer patients. PATIENTS AND METHODS: Between February 2018 and August 2019, 205 low-, intermediate- and high-risk prostate cancer patients were treated with SBRT using “CyberKnife M6” linear accelerator. In low-risk patients 7.5–8 Gy was delivered to the prostate gland by each fraction. For intermediate- and high-risk disease a dose of 7.5–8 Gy was delivered to the prostate and 6–6.5 Gy to the seminal vesicles by each fraction with a simultaneous integrated boost (SIB) technique. A total of 5 fractions (total dose 37.5–40 Gy) were given on every second working day. Acute radiotherapy-related genitourinary (GU) and gastrointestinal (GI) side effects were assessed using Radiation Therapy Oncology Group (RTOG) scoring system. RESULTS: Of the 205 patients (28 low-, 115 intermediate-, 62 high-risk) treated with SBRT, 203 (99%) completed the radiotherapy as planned. The duration of radiation therapy was 1 week and 3 days. The frequencies of acute radiotherapy-related side effects were as follows: GU grade 0 – 17.1%, grade I – 30.7%, grade II – 50.7%, grade III – 1.5%; and GI grade 0 – 62.4%, grade I–31.7%, grade II–5.9%, grade III–0%. None of the patients developed grade ≥ 4 acute toxicity. CONCLUSIONS: SBRT with a total dose of 37.5–40 Gy in 5 fractions appears to be a safe and well tolerated treatment option in patients with prostate cancer, associated with slight or moderate early side effects. Longer follow-up is needed to evaluate long-term toxicity and biochemical control.