Kate Johnson

May 19, 2011

May 19, 2011 (Montreal, Canada) — Multiparametric magnetic resonance imaging (MRI) can noninvasively detect local recurrence of prostate cancer with reasonable sensitivity and specificity compared with biopsy, according to a study presented here at the International Society for Magnetic Resonance in Medicine (ISMRM) 19th Annual Meeting and Exhibition.

Although transrectal ultrasound guided biopsy is normally used to identify local recurrence of prostate cancer after external beam radiotherapy, it may not sample the area of disease, explained Veronica A. Morgan, MSc, from Cancer Research UK and the Engineering and Physical Sciences Research Council Cancer Imaging Centre, Institute of Cancer Research and Royal Marsden National Health Service Foundation Trust, Sutton, Surrey, United Kingdom.

Similarly, traditional T2-weighted MRI sequences "often have insufficient contrast in previously irradiated prostate to enable differentiation between tumor and nontumor," she explained.

Multiparametric MRI integrates traditional T2-weighted imaging with 1 or more functional techniques — in this case, diffusion-weighted MRI — to differentiate the apparent diffusion coefficients (ADCs) of recurrent tumor and irradiated nontumor tissue, Ms. Morgan reported.

The study included 58 patients referred for endorectal MRI for suspected prostate cancer recurrence because of evidence of biochemical failure. Among these, 24 patients (aged 57 - 78 years) also had transrectal ultrasound guided biopsy within 14 months of MRI.

Postradiation prostate-specific antigen levels were between .05 and 23.8 ng/mL above nadir, and mean time from radiation therapy to MRI was 64 months.

The study compared the ADCs of MRI-defined tumor, biopsy-defined tumor, and nontumor irradiated tissue.

"The ADCs were almost identical regardless of whether they were identified by MRI or histology," said Ms. Morgan, "and the differences between tumor and nontumor in irradiated tissue were significant for both MRI and histology-defined tumor."

Using biopsy-defined tumor as the gold standard, the study found that multiparametric MRI combining T2-weighted and diffusion-weighted imaging had a sensitivity of 93.8% and a specificity of 75% for tumor detected, with a positive predictive value of 88.2% and a negative predictive value of 85.7%.

High sensitivity and specificity of detecting disease recurrence could be achieved with a cut-off ADC of 1201 (×10−6 mm2/second), which could predict tumor recurrence with a sensitivity of 92.3% and a specificity of 93.7%, Ms. Morgan said.

There were 2 cases in which ADC values appeared to be positive for recurrence, yet there was negative histology. "Biopsy used as the gold standard may have been subject to sampling error," she suggested, adding that correlation with MR-guided biopsy would be ideal.

"[Diffusion-weighted] MRI would be a useful adjunct to T2-weighted MRI in the investigation of prostate recurrence following external beam radiotherapy, as irradiated prostate has a significantly higher ADC than recurrent tumor, with ADC values equivalent to those published for nonirradiated prostate," Ms. Morgan concluded.

"All of agree that we need to do multiparametric MRI — we need to be able to fuse techniques in 1 workspace. The question is, which technique is best for a particular clinical scenario?" said Anwar Padhani, MB, BS, FRCP, FRCR, moderator of the session; honorary senior lecturer at University College, London; and consultant radiologist at the Paul Strickland Scanner Centre, Mount Vernon Cancer Centre, Northwood, Middlesex, England.

With regard to selection of patients for active surveillance, "the use of diffusion imaging for localization of recurrent tumor in the treated gland...is a really, really hot topic," he said.

Ms. Morgan and Dr. Padhani have disclosed no relevant financial relationships.

International Society for Magnetic Resonance in Medicine (ISMRM) 19th Annual Meeting and Exhibition: Abstract 48. Presented May 9, 2011.

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