At last week’s Genitourinary Cancers Symposium, Amini et al. presented the results of a data analysis that addresses the question of which kind of high-dose radiation therapy has the best cancer control rates (abstract no. 7; “Survival outcomes of dose-escalated external beam radiotherapy (DE-EBRT) versus combined brachytherapy for intermediate- and high-risk prostate cancer using the National Cancer Data Base”).
The authors probed the National Cancer Data Base (NCDB), found 20,279 high- and intermediate-risk patients who were treated between 2004 and 2006, and classified them into three treatment groups:
- Brachy boost: 40.0 to 50.4 Gy of EBRT + brachytherapy
- High-dose EBRT: 75.6 to 81.0 Gy of EBRT at 1.8 or 2 Gy per fraction (which included the very high-dose EBRT subset of patients immediately following)
- Very high-dose EBRT: 79.2 to 81.0 Gy of EBRT at 1.8 or 2 Gy per fraction
The use of ADT was not mentioned in this early poster.
Based on a median follow-up of 82 months, the survival analysis showed that:
- The brachy boost patients had better survival than the high-dose EBRT patients (hazard ratio [HR] = 0.75).
- Improvement was about the same for intermediate- and high-risk groups of patients.
- Brachy boost was not significantly better than very high-dose EBRT (HR = 0.91).
- The lack of incremental benefit held true for intermediate- and high-risk patients.
There was no analysis of toxicity. So, in this analysis, brachy boost had equivalent cancer control to the very high-dose EBRT that has become the standard of care.
A randomized clinical trial we looked at last year, ASCENDE-RT, came to the conclusion that brachy boost had better biochemical progression-free survival compared to 78 Gy of EBRT in both of these risk groups. Survival was so high, even with 9 years of follow-up, that it was too soon to detect significant survival differences. Urinary toxicity was, however, worse for the boost therapy.
We don’t know if a slightly higher EBRT dose would have rendered the two treatment options equivalent, as it did in the Amini study. We also can’t comment on the extent to which adjuvant ADT may have affected the difference in findings of the two studies. Patients in the NCDB analysis may be very different from patients in the ASCENDE-RT trial.
It’s tempting to choose the very high-dose EBRT based on this and the presumed lower toxicity compared to brachy boost therapy, but only a randomized clinical trial can provide the unbiased data we need to be definitive. Clearly, higher radiation doses, provided through any of several possible modalities, afford a higher potential for cancer control in intermediate- and high-risk men.
Editorial note: This commentary was written for The “New” Prostate Cancer InfoLink by Allen Edel.