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.