Evaluating the Phoenix definition of biochemical failure after (125)I prostate brachytherapy: Can PSA kinetics distinguish PSA failures from PSA bounces?
OBJECTIVE
To evaluate the prostate-specific antigen (PSA) kinetics of PSA failure (PSAf) and PSA bounce (PSAb) after permanent (125)I prostate brachytherapy (PB).


METHODS
The study included 1,006 consecutive low and "low tier" intermediate-risk patients treated with (125)I PB, with a potential minimum follow-up of 4 years. Patients who met the Phoenix definition of biochemical failure (nadir + 2 ng/mL(-1)) were identified. If the PSA subsequently fell to ≤0.5 ng/mL(-1)without intervention, this was considered a PSAb. All others were scored as true PSAf. Patient, tumor and dosimetric characteristics were compared between groups using the chi-square test and analysis of variance to evaluate factors associated with PSAf or PSAb.


RESULTS
Median follow-up was 54 months. Of the 1,006 men, 57 patients triggered the Phoenix definition of PSA failure, 32 (56%) were true PSAf, and 25 PSAb (44%). The median time to trigger nadir + 2 was 20.6 months (range, 6-36) vs. 49 mo (range, 12-83) for PSAb vs. PSAf groups (p < 0.001). The PSAb patients were significantly younger (p < 0.0001), had shorter time to reach the nadir (median 6 vs. 11.5 months, p = 0.001) and had a shorter PSA doubling time (p = 0.05). Men younger than age 70 who trigger nadir +2 PSA failure within 38 months of implant have an 80% likelihood of having PSAb and 20% chance of PSAf.


CONCLUSIONS
With adequate follow-up, 44% of PSA failures by the Phoenix definition in our cohort were found to be benign PSA bounces. Our study reinforces the need for adequate follow-up when reporting PB PSA outcomes, to ensure accurate estimates of treatment efficacy and to avoid unnecessary secondary interventions.
British Columbia Cancer Agency, Vancouver, BC, Canada.
Anna
A
Thompson
Mira
M
Keyes
Tom
T
Pickles
David
D
Palma
Veronika
V
Moravan
Ingrid
I
Spadinger
Vincent
V
Lapointe
W James
WJ
Morris
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001918:Brachytherapy / Q000379:methods*; D016009:Chi-Square Distribution; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000378:metabolism*; D011446:Prospective Studies; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D012016:Reference Values; D013739:Testosterone / Q000378:metabolism; D013997:Time Factors; D017211:Treatment Failure; D047368:Tumor Burden
D007457:Iodine Radioisotopes; D013739:Testosterone; D017430:Prostate-Specific Antigen