Hypofractionated boost to the dominant tumor region with intensity modulated stereotactic radiotherapy for prostate cancer: a sequential dose escalation pilot study.

Purpose To evaluate the feasibility, tolerability, and preliminary outcomes in patients with prostate cancer treated according to a hypofractionated dose escalation protocol to boost the dominant tumor-bearing region of the prostate. Methods and Materials After conventional fractionated external radiotherapy to 64 to 64.4Gy, 50 patients with nonmetastatic prostate cancer were treated with an intensity-modulated radiotherapy hypofractionated boost under stereotactic conditions to a reduced prostate volume to the dominant tumor region. A rectal balloon inflated with 60cc of air was used for internal organ immobilization. Five, 8, and 8 patients were sequentially treated with two fractions of 5, 6, or 7Gy, respectively (normalized total dose in 2Gy/fraction [NTD 2Gy ] 2Gy > 100Gy, high-dose group). Androgen deprivation was given to 33 patients. Acute and late toxicities were assessed according to the Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer (RTOG/EORTC) scoring system. Results Two patients presented with Grade 3 acute urinary toxicity. The 5-year probabilities of ≥Grade 2 late urinary and late low gastrointestinal (GI) toxicity–free survival were 82.2% ± 7.4% and 72.2% ± 7.6%, respectively. The incidence and severity of acute or late toxicities were not correlated with low- vs. high-dose groups, pelvic irradiation, age, or treatment with or without androgen deprivation. The 5-year biochemical disease–free survival (b-DFS) and disease-specific survival were 98% ± 1.9% and 100%, respectively. Conclusion Intensity-modulated radiotherapy hypofractionated boost dose escalation under stereotactic conditions was feasible, and showed excellent outcomes with acceptable long-term toxicity. This approach may well be considered an alternative to high-dose-rate brachytherapy.