Using Fiducial Markers to Aid in Prostate Cancer Radiation Treatment

Effective image-guided prostate therapies require excellent visualization of the prostate and surrounding anatomy, such that cancerous tissue can be treated while avoiding nearby neural and vascular structures. As such, Magnetic Resonance Imaging is well suited for image-guidance because of its excellent soft tissue contrast, multiplanar capabilities, and the potential to yield spectral/biological tumor mapping. Despite the potential for MRI-guided prostate therapies, there are currently no techniques that allow for precise trans-rectal intraprostatic needle placement in patients. In this pilot study we seek to validate the accuracy and tolerability of a new system and technique that allows for accurate placement of needles within the prostate based upon MR images. The method is very similar to transrectal ultrasound guided biopsy of the prostate, except that it is applicable within a closed high-field MRI scanner. Four gold fiducial markers will be placed within the prostate under needle guidance in a series of patients with localized prostate cancer before external beam radiotherapy. Fifteen patients will be enrolled onto this study with sample size determined to obtain reasonably precise estimates of mean placement accuracy. The accrual period is expected to be less than a year. While placement of the fiducial markers has no direct therapeutic benefit for the patient, intraprostatic radiopaque fiducial markers (placed under ultrasound) have shown value in assessing daily setup errors and off-line organ motion during external beam radiation therapy for prostate cancer. Therefore, a secondary objective is to gain experience using these intraprostatic fiducial markers for daily assessment and adjustment of external radiation beam targeting. These markers can also be utilized to aid in CT-MRI fusion and results in better target delineation for treatment planning. In this way, prostate cancer patients who are receiving external-beam radiation therapy may benefit from participation.