Radiotherapy Method Impacts Survival, Risk of Metastases in Prostate Cancer

Brachytherapy boost (BTB) was associated with improved survival and a lower risk of distant metastases compared with external beam radiotherapy (EBRT) for intermediate- and high-risk prostate cancer in a study published in the journal Radiotherapy and Oncology.

Combination treatment with BTB and EBRT has been shown to improve disease control in patients with intermediate- and high-risk prostate cancer, either in tandem with androgen deprivation therapy (ADT) or without ADT, the study authors noted. However, the randomized prospective trials demonstrating this trend were small and were not powered to show significant differences in terms of overall survival (OS) or freedom from distant metastases (FFDM).

The authors of the current study aimed to determine whether there was an association between BTB and OS or FFDM outcomes in a larger, multi-institutional data set and with longer follow-up time.

“To our best knowledge, this study was based on the largest propensity-score matching analysis of intermediate- and high-risk [prostate cancer] patients undergoing radical EBRT or BTB combined with ADT,” the authors wrote. The main end points were OS, FFDM, and metastasis-free survival (MFS).

A total of 1641 patients who were treated with EBRT or high-dose-rate BTB for intermediate- or high-risk prostate cancer at 2 tertiary institutions were included in the study. Of those patients, 1548 (94.3%) were treated with ADT, 1148 (70%) were treated with EBRT, and 493 (30%) were treated with high-dose-rate BTB. In 127 cases (74.2%), this included whole pelvic radiotherapy (WPRT).

The median (IQR) survival was 117.8 (78-143.3) months, and median follow-up was 60.7 months. Patients treated between January 2003 and December 2014 were included in the study.

The method of radiotherapy was an independent prognostic factor for OS, FFDM, and MFS in the cohort. BTB was associated with improved OS (HR, 0.75; 95% CI, 0.63-0.88; P < .001), FFDM (HR, 0.54; 95% CI, 0.4-0.73; P < .001), and MFS (HR, 0.72; 95%, CI, 0.61-0.85; P < 0.001).

Although the initial EBRT and BTB groups differed in age, maximum prostate-specific antigen levels, International Society of Urologic Pathologists grade group, and TNM T stage, the groups were well balanced after propensity score matching and there were no statistically significant differences in the remaining 986 patients. Consistent results were found in a separate analysis conducted with risk-group stratification.

“Using the multi-center propensity-score matching analysis, with a large study group and long follow-up, we were able to show that the BTB was associated with improved survival and a decreased rate of distant metastases,” the study authors wrote. “We believe that this is an important finding that could help increase the use of BTB as a cost-effective and efficient method for improving clinical outcomes in patients with intermediate- and high-risk prostate cancer.”

The study was limited by its retrospective nature, as well as changing ADT and radiotherapy regimens as radiotherapy delivery and planning techniques improved over the study’s time frame. There was also insufficient data for comorbidity adjustments despite the use of propensity score matching.

While future randomized trials are need to confirm the potential OS benefits of BTB, the current study showed a strong correlation between BTB and OS, FFDM, and MFS in patients with intermediate- and high-risk prostate cancer.

Reference

Miszcyk M, Magrowski Ł, Krzysztofiak T. Brachytherapy boost improves survival and decreases risk of developing distant metastases compared to external beam radiotherapy alone in intermediate and high risk group prostate cancer patients. Radiother Oncol. Published online March 22, 2023. doi:10.1016/j.radonc.2023.109632