Researchers report outcomes of low-dose RT brachytherapy after EBRT for prostate most cancers

Researchers involved in the Phase II NRG Oncology RTOG 0526 study to investigate low dose rate (LDR) prostate brachytherapy (BT) after local recurrence (LR) after external radiation therapy (EBRT) in low to medium risk prostate cancer patients reported late grade 3 gastrointestinal and urogenital adverse events (AEs) that occurred in 14% of study participants. The results of a follow-up examination of at least 5-year-old patients who participated in the study suggest that the 5-year freedom from biochemical failure (BF) is 68% and remains constant at a 10-year rate of 54%. This report was presented at the virtual edition of the American Society for Radiation Oncology (ASTRO) annual meeting in October 2020.

Low and medium risk prostate cancer typically occurs locally in 10 to 30% of men after EBRT. Prior to this study, most of the available data on salvage brachytherapy for prostate cancer were retrospective and came from single-center studies with multiple variables related to dose and technique. In view of the high recurrence rate of this patient population, it was crucial to expand the data on this modality in a multicenter study with defined methods. "

Juanita M. Crook, MD, FRCPC, of ​​the Cancer Center for the Southern Interior of the University of British Columbia and the lead author of the NRG-RTOG 0526 abstract

To be eligible for NRG-RTOG 0526, prostate cancer patients must have had low or medium risk prostate cancer prior to EBRT and have a proven LR 30 or more months after their EBRT. 92 patients were analyzed for the study and followed for at least 5 years after their salvage brachytherapy. Participants in NRG-RTOG 0526 received a minimum dose of 140 Gy with I-125 or 120 G with Pd-103. Researchers tracked clinical outcomes at 5 years or longer, including goals such as disease-specific survival, overall survival, time to biochemical failure, and patterns of relapse.

As originally reported, 14% of the participants developed grade 3 gastrointestinal and urogenital AEs with a mean follow-up time of 6.9 years. The mean prior EBRT dose was 74 Gy and the mean interval since receiving EBRT was 85 months. Androgen deprivation therapy was combined with Salvage BT in only 16% of the cases.

The 5-year rate of biochemical failure was 68%, which is comparable to other salvage modalities. After 10 years the biochemical failure rate was 54% (95% CI: 43-66). Disease-free survival at 5 years was 61% but dropped to 33% at 10 years. Nineteen patients died. Four patients had local relapse (5% at 10 years) and 14 had remote failure with a 10-year rate of 19% (95% CI: 10-29). None of the clinical or treatment factors were significantly related to participants' overall survival, disease-free survival, or local, distant, or biochemical failure.

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