Highly hypofractionated biaxially rotational dynamic radiation therapy (BROAD-RT) for high-risk prostate cancer.

To report clinical outcomes following highly hypofractionated biaxially rotational dynamic radiation therapy (BROAD-RT), a unique radiation therapy method that facilitates non-coplanar volumetric-modulated arc therapy (VMAT) without the need to rotate the couch or reposition the patient, for high-risk prostate cancer (PCa) with simultaneous integrated boost (SIB) for intra-prostatic dominant lesions (IPDLs), we performed a single-center prospective pilot study. In this study, patients with high-risk PCa according to the D'Amico classification or those with cT3aN0M0 PCa were eligible. VMAT was performed using BROAD-RT, and a dose of 54 Gy in 15 fractions was prescribed for the prostate in combination with SIB for IPDLs at a dose of 57 Gy in 15 fractions. Short-term neoadjuvant androgen-deprivation therapy (median: 6.9 months) was conducted. Neither adjuvant androgen-deprivation therapy nor fiducial marker implantation to the prostate was applied for any patient. In total, 26 patients were registered in this study between August 2018 and November 2020. Their median age was 73 years at the initiation of RT. The median follow-up period was 49.7 months. The 4-year cumulative incidence rates of grade 2 late GU and GI toxicities were 15.4 and 3.8%, respectively. No grade 3 or higher acute or late toxicities were observed. The 4-year biochemical failure-free survival rates were 87.7%. In conclusion, highly hypofractionated RT using BROAD-RT for high-risk PCa with SIB for IPDLs was feasible and facilitated favorable oncological outcomes. Therefore, this approach is considered a promising method to achieve safe dose escalation and shorten the treatment duration.