ESTRO 2024 - Abstract Book

S2648

Clinical - Urology

ESTRO 2024

1 KU Leuven, Department of Oncology, Leuven, Belgium. 2 University Hospitals Leuven, Department of Radiation Oncology, Leuven, Belgium. 3 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, Netherlands. 4 University Medical Center Utrecht, Department of Radiation Oncology, Utrecht, Netherlands. 5 Radboud University Medical Center, Department of Radiation Oncology, Nijmegen, Netherlands. 6 University Medical Center Utrecht, Julius Center for Health Sciences and Primary Care, Utrecht, Netherlands

Purpose/Objective:

The phase III FLAME trial (NCT01168479) demonstrated that focal boosting of the macroscopic visible tumor with external beam radiotherapy increases the biochemical disease-free survival (bDFS) in patients with intermediate- and high-risk prostate cancer (PCa). In parallel, the phase III PACE-B trial (NCT01584258) showed that whole gland stereotactic body radiotherapy (SBRT) is noninferior to conventional external beam radiotherapy for low- and favorable-intermediate-risk PCa. In the hypo-FLAME trial (NCT02853110), both, the focal boosting strategy and SBRT for PCa, were brought together and this was associated with acceptable acute genitourinary (GU) and gastrointestinal (GI) toxicity. The 5-year analysis of the hypo-FLAME trial investigated the long-term safety and efficacy of prostate SBRT with iso-toxic focal boosting in patients with intermediate- and high-risk PCa.

Material/Methods:

Patients with intermediate- or high-risk PCa were enrolled in a multicenter, prospective phase II trial. All patients were treated with ultrahypofractionated doses of 35 Gy in 5 weekly fractions to the whole prostate gland with an integrated boost up to 50 Gy to the multiparametric MRI-defined tumor(s). If the dose constraints to the normal tissues were at risk, these were prioritised over the aimed boost dose, striving for iso-toxic focal boosting. The current analysis reports on the secondary endpoints, which include the 5-year bDFS and late toxicity measured by the CTCAE v4.0.

Results:

Between April 2016 and December 2018, 100 men were treated in 4 academic centres. In December 2023, all patients had a minimum follow-up of 5 years. At baseline, median age of the included patients was 73 years. According to the EAU risk classification, 75% of the patients were classified as having high-risk PCa. Hormone therapy was prescribed to the majority of patients (62%). Due to normal tissue constraints, the aimed dose of 50 Gy was in most cases not achieved. The median mean dose delivered to the visible tumor nodule(s) on multiparametric MRI was 44.7 Gy. At 5-year follow-up, 6 patients relapsed according to the Phoenix definition, resulting in an estimated 5-year bDFS (95% CI) of 93% (86% - 97%). Furthermore, for 2 patients, the PSA value reached the criteria for biochemical failure with a subsequent spontaneous decrease below these criteria. Both were classified as a benign PSA bounce. At 5 years, the prevalence of grade 2+ GU and GI toxicity was 12% (10/85 patients) and 4% (3/85 patients), respectively (Figure 1). The reported cumulative incidence of late grade 3 toxicity was 2% for GU and 1% for GI toxicity.