Prostate gland: MR imaging appearance after vascular targeted photodynamic therapy with palladium-bacteriopheophorbide.

PURPOSE

To prospectively evaluate the magnetic resonance (MR) imaging appearance of the prostate and periprostatic tissues after vascular targeted photodynamic therapy (VTP) with palladium-bacteriopheophorbide for locally recurrent carcinoma after external beam radiation therapy.

MATERIALS AND METHODS

Informed consent was obtained from all patients, and approval was obtained from the ethics review boards of all participating institutions. Nonenhanced T2-weighted and dynamic gadolinium-enhanced T1-weighted MR imaging examinations were performed at baseline and 1 week, 4 weeks, and 6 months after VTP in 25 men (age range, 58-83 years; mean age, 73 years) as part of a prospective phase I/II trial. Percentage of MR-depicted necrosis was defined as the volume of nonenhancing prostatic tissue 1 week after VTP divided by the volume of the prostate. Patterns of intra- and extraprostatic necrosis were recorded. Pearson correlation coefficients were used to test correlations between necrosis and prostate-specific antigen level.

RESULTS

Contrast material-enhanced T1-weighted MR images obtained 1 week after therapy showed necrosis in all patients. Treatment margins were irregular in 21 of 25 patients. T2-weighted images showed no clear treatment boundaries in any patient. Extraprostatic necrosis involved the puborectalis or levator ani muscles in 22, obturator internus muscle in 12, periprostatic veins in three, pubic bone marrow in four, and anterior rectal wall in nine of the 25 patients. The neurovascular bundle appeared to be spared in all patients. Percentage of MR-depicted intraprostatic necrosis was correlated with percentage decrease in prostate-specific antigen level (from baseline) at 4 weeks (r=0.41, P=.04) and 12 weeks (r=0.45, P=.02).

CONCLUSION

Contrast-enhanced MR imaging depicts irregular margins of intraprostatic treatment effect. This finding suggests varied tissue sensitivities to VTP with palladium-bacteriopheophorbide.