Regardless of the type of treatment administered, serial measurements of PSA and DRE are the standard tools used to monitor for tumor recurrence. When recurrence is suspected due to a rising PSA or because a nodule or induration has been felt on DRE, imaging may be useful to confirm the presence of recurrence and to determine whether it is local or systemic.

Detection of local recurrence after radiation therapy
In patients who have undergone radiation therapy, MRI and MRSI may provide a target for biopsy and may help to determine the location, extent, and size of recurrence to improve treatment selection and planning. In one study [42] two radiologists used MRI to evaluate prostate cancer recurrence after radiation treatment in 45 patients scheduled for salvage prostatectomy.  They achieved sensitivity/specificity values of 76%/73% and 55%/65% for tumor detection by quadrant, 86%/84% and 64%/76% for extracapsular extension, and 58%/96% and 42%/96% for seminal vesicle invasion - values similar to those found in studies of untreated patients [42]. Furthermore, in a small preliminary study that also used step-section pathology as the standard of reference, MRI and MRSI had higher sensitivities (68% and 77%, respectively) than DRE (16%) and TRUS-guided biopsy (48%) for the detection of recurrence after radiation therapy, although MRSI had lower specificity (78%) than the three other modalities, each of which had a specificity greater than 90% [43].

In a study of nine patients who underwent salvage prostatectomy,  investigators compared the locations and volumes of prostate cancer lesions on preradiation-therapy MRI, post-radiation therapy MRI, and step-section pathology maps.

They found that in every patient, clinically significant local recurrence occurred at the site of the original primary tumor [44]. These results provide support for the concept of boosting the radiation dose to the primary tumor using imaging guidance; they also suggest that the use of MRI before and after radiation treatment to identify and monitor the site of the primary tumor might facilitate detection of cancer recurrence at an earlier stage, when it is more likely to be treatable by salvage prostatectomy [44].

Detection of local recurrence after radical prostatectomy
Magnetic resonance imaging has demonstrated the capacity to detect local recurrence in many patients with a rising PSA but no palpable tumor in the prostatic fossa [45, 46]. Magnetic resonance imaging may show local recurrences in the perianastomotic and retrovesical regions [47]. In addition, MRI has demonstrated that 30% of local recurrences may occur at other sites in the pelvis, for example in retained seminal vesicles or at the lateral or anterior surgical margins [45].

While MRI can detect recurrent cancer that is not palpable, confirmation of MRI abnormalities by needle biopsy is recommended before therapeutic intervention (e.g., boost dose of salvage irradiation to nodules or addition of androgen-deprivation therapy to salvage radiation therapy). One limiting feature of MRI-detected local recurrence, especially if impalpable, is the difficulty of ultrasound-guided biopsy of abnormalities identified on MRI, as many suspected lesions will not be visible sonographically.

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Hedvig Hricak and Peter T. Scardino
Prostate Cancer, eds. Hedvig Hricak and Peter T. Scardino. Published by Cambridge University Press.
© Cambridge University Press 2009.

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