3D MR-spectroscopic imaging assessment of metabolic activity in the prostate during the PSA "bounce" following 125iodine brachytherapy.
OBJECTIVE
A temporary increase in prostate-specific antigen (PSA) values is observed in 30%-40% of men following (125)I brachytherapy (BT) for prostate cancer. We present the results of a study to characterize prostate metabolic activity during the PSA "bounce" and to correlate metabolic changes with PSA levels using three-dimensional magnetic resonance spectroscopic imaging (3D-MRSI).


METHODS
3D-MRSI was performed in 24 patients during the PSA bounce. Eight of these had also had a baseline 3D-MRSI scan before BT for the purpose of tumor mapping. The 3D-MRSI was repeated at 6- and 12-month intervals, and PSA levels were monitored every 3 months. Twenty-one of the patients had favorable-risk prostate cancer, and 3 had intermediate risk.


RESULTS
The choline+creatine signal intensity, although markedly reduced, was observable following BT. Diffuse activity not corresponding to original biopsy-positive sites was observed in 22 cases, and 2 cases were documented to have local recurrence. No statistically significant correlation between metabolic activity and PSA levels at each interval was found.


CONCLUSIONS
Post-BT prostate 3D-MRSI shows evidence of diffuse metabolic activity unrelated to residual malignancy. This supports the benign nature of the PSA bounce and suggests an inflammatory etiology. In the situation of a rising PSA, observation of focal activity on MRI/3D-MRSI could be a useful adjunct to suggest local recurrence at an earlier interval after brachytherapy when prostate biopsies would still be unhelpful. Longer follow-up is necessary to confirm the complex relationship between metabolic activity and PSA levels.
Kirilova
Anna
A
Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, Canada.
Damyanovich
Andrei
A
Crook
Juanita
J
Jezioranski
John
J
Wallace
Kris
K
Pintilie
Melania
M
D001918:Brachytherapy / Q000379:methods*; D002794:Choline / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis / Q000378:metabolism; D011467:Prostate / Q000378:metabolism*; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000378:metabolism* / Q000532:radiotherapy*; D018709:Statistics, Nonparametric; D013997:Time Factors
D007457:Iodine Radioisotopes; D019343:Citric Acid; D017430:Prostate-Specific Antigen; D003401:Creatine; D002794:Choline