Brachytherapy outperforms EBRT in Asians with prostate cancer

Low-dose-rate brachytherapy (LDR-BT) provides a better biochemical failure-free survival (bFFS) rate than external beam radiation therapy (EBRT) in Asian men with intermediate-risk prostate cancer, according to a recent Singapore study.

“Brachytherapy delivers an ablative dose to the entire glands but also exposes a higher dose to normal tissue,” the researchers said. “Our results demonstrated a higher rate of genitorurinary (GU) toxicities in LDR-BT, especially urethra stricture [requiring] surgical intervention.”

The present retrospective study included 642 men (median age 69 years) with biopsy-proven low- and intermediate-risk prostate cancer. Treatment modalities were EBRT in 521 patients and LDR-BT in 121. Study outcomes were bFFS, defined as time from diagnosis to biochemical recurrence or all-cause death, and overall survival (OS).

In the low-risk EBRT cohort, the median follow-up was 7.6 years, during which the 5- and 10-year bFFS estimates were 87 percent and 70 percent, respectively. Corresponding rates were higher for the LDR-BT group (92 percent and 85 percent; median follow-up, 8.6 years), though not significantly so (hazard ratio [HR], 1.9, 95 percent confidence interval [CI], 0.9–4.0; p=0.08). [Acta Oncol 2021;doi:10.1080/0284186X.2021.1950921]

OS was likewise comparable between modalities in low-risk patients (HR, 2.1, 95 percent CI, 0.7–6.2; p=0.2).

On the other hand, intermediate-risk patients saw significantly greater benefit with LDR-TB which yielded 5- and 10-year bFFS estimates of 96 percent and 86 percent, respectively, as opposed to EBRT which delivered corresponding rates of 89 percent and 61 percent (HR, 2.8, 95 percent CI, 1.1–6.9; p=0.02). Median follow-ups for the respective treatment arms were 8.4 and 6.9 years.

OS remained unaffected by treatment modality in intermediate-risk participants (HR, 1.7, 95 percent CI, 0.7–4.2; p=0.3).

Multivariable analysis confirmed that compared to LDR-BT, EBRT was associated with significantly inferior bFFS rates (HR, 3.1, 95 percent CI, 1.2–8.0; p=0.017).

In terms of safety, GU toxicities grade 2 and above were documented in 9 percent of patients in the LDR-TB arm, as opposed to only 3 percent in the EBRT group. Gastrointestinal toxicities grade 2 and above were present only in the EBRT group (3 percent).

All-cause and prostate cancer-related deaths occurred in 11 percent and 2 percent of the EBRT arm, and in 8 percent and 2 percent of the LDR-TB arm, respectively.

“Overall, prostate cancer-specific death was low in both cohorts, and all cause of death are similar between two treatment groups,” the researchers said.

Limitations of the current study include its retrospective design, relatively short follow-up, and insufficient between-arm matching regarding known prognostic clinical and pathological factors.

“Despite these limitations, our study added long-term data of the Asian population to the existing literature of EBRT and LDR-BT in low- and intermediate-risk prostate cancer,” the researchers said. “Direct comparison of LDR and contemporary EBRT regimens, especially moderate- and ultra-hypofractionation, are needed for future studies.”