Stereotactic body-radiotherapy boost dose of 18 Gy vs 21 Gy in combination with androgen-deprivation therapy and whole-pelvic radiotherapy for intermediate- or high-risk prostate cancer: a study protocol for a randomized controlled, pilot trial

BACKGROUND Combination therapy using external-beam radiotherapy (EBRT) with a brachytherapy boost has demonstrated superior biochemical control than dose-escalated EBRT alone. Whereas brachytherapy is disadvantageous because it is an invasive procedure, stereotactic body-radiotherapy (SBRT) using CyberKnife could emulate the dose distribution of brachytherapy and is a non-invasive and safe modality to control intra-fractional movement. We therefore adopted SBRT using CyberKnife as a boost therapy after whole-pelvic radiotherapy (WPRT). METHODS/DESIGN In this prospective, randomized, single-center, pilot study for intermediate- and high-risk prostate cancer without nodal or distant metastasis, after androgen-deprivation therapy and WPRT, patients will be randomized to one of two SBRT boost regimens, i.e., 18 or 21 Gy administered in three fractions every other day. DISCUSSION The aim of this trial is to evaluate acute toxicities using both physician- and patient-reported outcomes and short-term biochemical control with SBRT boost following WPRT. Additionally, chronic toxicities and long-term biochemical control will be evaluated as secondary endpoints in this trial. Based on the generated results, we will plan the full-scale phase II study for selecting the SBRT boost dose. TRIAL REGISTRATION ClinicalTrials.gov, ID; NCT03322020 . Retrospectively registered on 26 October 2017.