An analysis of 4 SBRT of low and intermediate risk prostate cancer was conducted for the evaluation of the incidence of prostate specific antigen bounce and its correlation with the time dose fraction schedule. The correlation between bounce with PSA response at four years and biochemical failure-free survival (BFFS) was also explored in this study.
The study included four treatment groups:
- 35 Gy/five fractions once in a week (TG-1),
- 40 Gy/five fractions once a week (TG-2),
- 40 Gy/five fractions every other day (TG-3),
- and 26 Gy/two fractions once a week (TG-4).
In total, 287 patients were involved in this study with a follow-up of five years. The five year cumulative incidence of bounce by nadir + 2.0 was 8%. The two year incidences of PSA bounce by nadir + 0.2 were 28.9%, 21%, 19.6% and 16.7% and were 7.2%, 8%, 2.7% and 6.7% by nadir +2.0 for TG-1,2,3 and 4, respectively. PSA bounce by nadir + 0.2 and nadir + 2.0 was associated with a lower probability of PSA response at four years; there was no association between bounce by nadir + 0.2 or nadir + 2 with BFFS.
The incidence of PSA bounce was not dependent upon the time dose fraction schedule for prostate SBRT. One out of 13 patients experienced a bounce high enough to be misinterpreted as a biochemical failure, and clinicians should avoid early salvage interventions in these patients. In conclusion, no association between PSA bounce and BFFS was found.