Fiducial markers are small, radiopaque implants, typically tiny gold seeds, coils, or cylinders about the size of a grain of rice. They are necessary before certain types of prostate radiation therapy. These markers serve as internal reference points, allowing the radiation team to precisely locate the prostate gland during treatment. This ensures that radiation beams are accurately directed to the target area, minimizing the dose to surrounding healthy tissues.
Necessity of Precision Targeting in Prostate Radiation
The prostate gland is a soft organ located within the pelvis. Its position shifts daily due to the natural filling and emptying of the rectum and bladder. This movement challenges radiation therapy, which requires millimeter-level accuracy to be effective.
Fiducial markers enable Image-Guided Radiation Therapy (IGRT). IGRT allows the radiation machine to image the target area just before or during each treatment session. Because the gold markers are highly visible on imaging scans, they act as a proxy for the prostate’s location. This tracking ensures the radiation dose is concentrated on the target, sparing nearby healthy organs like the rectum and bladder. Without these fixed reference points, larger treatment margins would be necessary, increasing the risk of damaging normal tissue.
Patient Preparation Before the Procedure
Before marker placement, patients follow specific instructions to reduce infection risk and optimize prostate visualization. Since the procedure often uses a transrectal approach, a prophylactic, broad-spectrum oral antibiotic is prescribed. This medication is taken before and sometimes after the procedure to safeguard against potential bacterial introduction from the rectal area.
Patients are also instructed to perform a bowel preparation, such as a saline enema, the night before or morning of the procedure to clear the rectum. This minimizes contents that could interfere with imaging guidance or insertion. If mild sedation or general anesthesia is used, fasting instructions are given, requiring the patient to refrain from eating or drinking after midnight. Before the procedure, the patient is positioned comfortably, often lying on their side, and informed consent is confirmed.
The Marker Placement Procedure
Marker placement is typically an outpatient procedure performed by a urologist or radiation oncologist. The first step involves Transrectal Ultrasound (TRUS) imaging. A small ultrasound probe is gently inserted into the rectum, emitting sound waves that create a real-time image of the prostate gland. This allows the clinician to precisely map the organ’s structure.
Before insertion, a local anesthetic, such as lidocaine, is injected to numb the tissue around the prostate and rectal wall, minimizing discomfort. The most common technique is the transrectal approach, similar to a prostate biopsy. A specialized, thin needle is guided through the rectal wall and into the prostate under continuous TRUS visualization.
The clinician strategically places three to five markers into the prostate gland. These markers are distributed in a pattern—often at the base, apex, and middle—to define the gland’s three-dimensional position and rotation. Once the markers are deployed and secured within the prostate tissue, the needle is withdrawn. The procedure is usually complete within 15 to 20 minutes.
Post-Procedure Steps and Treatment Planning
Following placement, patients are monitored briefly before being released to a care partner, allowing any sedation effects to wear off. Patients may experience minor, temporary side effects, including a small amount of blood in their urine, stool, or semen for several days to a few weeks.
Mild discomfort or soreness in the perineal area can be managed with over-the-counter pain relievers. Patients are advised to avoid strenuous activity for three to five days. The implanted markers serve as the foundation for radiation treatment planning.
A few days to a week after placement, the patient undergoes a dedicated imaging session, often a CT scan or MRI, known as a simulation. The gold markers appear brightly on these images, allowing the medical physicist and radiation oncologist to define the boundaries of the target area. They then calculate the necessary radiation doses (dosimetry) and create a personalized treatment plan.