Stereotactic body radiotherapy for prostate cancer: treatment approaches and clinical outcomes.

Extreme hypofractionation may be a radiobiologically sound strategy against prostate cancer cells with presumed low radiosensitivity (α) and high repair capacity (β) to small treatment fractions. In this case, large doses per fraction may be more effective in the tumor cell killing. Hence, the fractionation sensitivity differential (tumor/normal tissue) favors the use of hypofractionated radiotherapy (RT) as tumor α/β values are lower than the values considered for late normal-tissue morbidity. High-dose rate brachytherapy (HDR-BT) and stereotactic body RT (SBRT) are competing extreme hypofractionated treatment methods aiming to efficiently escalate the dose against prostate cancer. Focal treatment strategies to the dominant and non-dominant tumor nodules inside the prostate have been considered with both treatment approaches.The present status of SBRT for prostate cancer is presented as well as a comparative summary of the existing studies on partial prostate boost irradiation either with HDR-BT or SBRT. Extreme hypofractionation (i.e., >6 Gy/fraction) still deserves investigation in prospective trials provided that the precaution is taken to assure an homogeneous tumor dose distribution, a short overall treament time (<5 weeks), and an optimally short fraction duration.