A newly published report from an Australian research group compares the outcomes of two sets of patients treated for intermediate- and high-risk prostate cancer with a single schedule of either external beam radiation therapy (EBRT) alone or EBRT + a high-dose-rate brachytherapy (HDRB) boost.
Khor et al. report on data from a series of 334 patients with definitive internmediate- or high-risk prostate cancer, all of whom were treated (between 2001 and 2006) with EBRT + an HDRB boost. The prescribed dose of EBRT was 46 Gy in 23 fractions, with an HDRB boost of 19.5 Gy in 3 fractions. The data from this cohort of patients was then compared to a matched pair set of contemporaneously treated men (also all diagnosed with intermediate- or high-risk prostate cancer) who were treated with EBRT alone (to 74 Gy in 37 fractions).
It should be noted immediately that the form of EBRT used to treat these men (in both cohorts of men) was three-dimensional conformal EBRTradiation therapy or 3D-CRT (as opposed to the clearly superior IMRT or IGRT forms of EBRT). No one was getting the type of fiducial gold markers now used to improve the accuracy of delivery of radiation therapy either. It should also be noted that this was not a prospective, randomized or controlled clinical trial. we should be careful about over-interpreting the outcomes data.
Here are the basic study findings:
- The study encompassed 688 men with intermediate- and high-risk prostate cancer.
- 344 prospectively enrolled men were treated with 3D-CRT + HDRB.
- 344 matched patients were treated with 3D-CRT alone.
- 41 percent of the patients in each cohort had high-risk disease.
- Average (median) follow-up for signs of biochemical or other forms of failure was 60.5 months.
- The 5-year freedom from biochemical failure was
- 79.8 percent for men treated with 3D-CRT + HDRB
- 70.9 percent for men treated with 3D-CRT alone
- The hazard ratio (HR) was 0.59 and was statistically significant.
- There was no alteration in efficacy of 3D-CRT + HDRB when planned androgen deprivation therapy was also administered.
- There was a strong trend toward reduced efficacy of 3D-HRT + HDRB compared to 3D-CRTR alone in high-risk cases.
- Rates of grade 3 urethral stricture were
- 11.8 percent among men treated with 3D-CRT + HDRB
- 0.3 percent among men treated with 3D-CRT alone
- There were no observable differences in clinical outcomes.
The authors conclude that men treated with 3D-CRT + HDRB showed higher freedom from biochemical progression than those treated with 3D-CRT alone (particularly in the intermediate-risk patients). However, they also point out that this improvement in biochemical progression had to be balanced against the increased risk of urethral toxicity.
In the “modern” world of highly targetable IMRT and IGRT, it appears increasingly questionable whether HDRB is really a necessary or useful method of treatment when combined with EBRT. This study suggests that at best the value of HDRB may be limited to intermediate-risk patients … and even then it comes with a considerable risk for urethral toxicity.