Evaluation of Intraprostatic Fiducial Markers For External Beam Radiation Therapy

The prostate may change position on a day-to-day basis due to differences in positioning, muscle tone, rectal filling, and bladder filling. Soft tissue like the prostate is not usually visible with normal x-rays, but certain metals like gold are visible. Many institutions are using an FDA-approved system (fiducial system), the one being used in this study, which involves implanting small gold markers to locate the prostate on a daily basis. This system allows the prostate to be located before treatment, which may improve radiation delivery to the prostate and decrease radiation exposure to normal tissue such as the rectum and bladder. The ability of this system to provide information on the location of the prostate before treatment should allow for more precise and accurate radiation treatment of prostate cancer. The small implanted gold markers are 3 mm long and 1 mm wide (about the size of a grain of rice). If you agree to take part in this study, 3 markers will be permanently implanted into your prostate using a needle similar to the biopsy needle used to diagnose your cancer. Treatment for prostate cancer during this research study will not be different from the MD Anderson standard of care. You will have intensity-modulated radiation therapy (IMRT) treatment for the prostate cancer performed using the CT-Linac treatment machine (ExaCT, Varian Medical Systems, Palo Alto, CA). This machine will have the same IMRT capabilities as other treatment machines in the Radiation Oncology Department. During the study, the position of the gold markers seen on x-ray will be used to make adjustments to the position of your prostate for your radiation therapy treatment. The positions reported by the fiducial system will be recorded and used for daily treatment. Three (3) times per week, you will have a CT scan of your prostate. The CT scans will be performed just before the delivery of radiation. Radiotherapists will assist you onto the treatment table and position it for your treatment. The treatment table will then be rotated 180 degrees from the treatment machine and the CT scan of your prostate will be performed. After the CT scan, which will take about 5-8 minutes, the couch will be rotated back to the original position. A trans-abdominal ultrasound of your prostate will also be performed twice per week for the first two weeks and then once a week from then on while you are on study. The MD Anderson staff and researchers will analyze the changes in prostate movement during radiation therapy using the scanned CT images and ultrasound images and compare them with positional changes displayed by the fiducial-based system. Targeting of your prostate on a daily basis will be performed using the fiducial-based system. This will involve performing a pair of x-rays before your treatment. A shift will be made if needed using the implanted prostate markers. The position of the seeds after the shift will be routinely verified with another pair of x-rays. After alignment has occurred, a radiation treatment will then be delivered. This is an investigational study. The fiducial-based system is FDA-approved. A total of 20 patients will take part in this study. All will be enrolled at MD Anderson.