Radiation therapy uses high-energy beams to precisely target and destroy cancer cells while sparing surrounding healthy tissue. This treatment requires extremely accurate daily positioning. To guarantee this accuracy, radiation oncologists use small, permanent skin markings, often called radiation tattoos or alignment marks. These tiny tattoos serve as fixed external reference points, allowing therapists to consistently reproduce the patient’s exact position throughout the entire course of treatment.
The Purpose and Placement of Alignment Marks
The primary function of alignment marks is to provide a fixed coordinate system on the patient’s body for daily setup. Before the first treatment, a planning session called a CT simulation maps the tumor’s location relative to the patient’s external anatomy. The radiation therapist uses room-mounted lasers to project coordinates onto the skin, marking the precise location where the radiation beam’s center, or isocenter, will enter the body.
A set of these marks is placed in strategic locations to define the treatment field in three dimensions. Patients typically receive between one and five marks, depending on the area being treated and the complexity of the plan. A common setup involves a central reference point and two or more lateral marks to create a geometric framework. Aligning these tattooed points with the linear accelerator’s laser system ensures the patient is in the identical position for each daily fraction.
Physical Appearance and Dimensions
Radiation tattoos are designed for function, not aesthetics. These marks are exceptionally small, often described as the size of a pinprick or a small freckle. Their diameter is typically just 1 to 2 millimeters, making them discreet yet perfectly visible to the trained eye.
The color is most frequently a dark hue, such as black or dark blue, created using a small drop of India ink deposited beneath the skin’s surface. Some specialized centers use faint pink or colorless ultraviolet-responsive ink, which is nearly invisible under normal light but clear when illuminated by a special UV light. They present as a small, clean, perfect dot, lacking the variation associated with larger tattoos. The precise shape is intentional, as any visual distortion would compromise the geometric accuracy required for treatment.
The Marking Procedure
The application of alignment marks occurs during the CT simulation appointment, the initial planning session for the treatment course. After the radiation oncologist and physicist finalize the treatment plan and identify the isocenter coordinates, the therapist marks the skin. The area is first sterilized with an alcohol wipe before a tiny drop of ink is placed on the precise location.
A specialized, sterile, fine-gauge needle or an electric marking pen is then used to puncture only the top layers of the skin, depositing the ink. The process is extremely quick, often feeling like a momentary pinch or a mosquito bite, and is completed in seconds with minimal discomfort. Along with these permanent dots, the treatment team may also use temporary marker lines to outline the larger treatment field for initial setup, which patients wash off after the first day.
Longevity and Management
The marks placed for radiation therapy are permanent tattoos, designed to remain on the skin indefinitely. This permanence acts as a safeguard and a historical reference point should the patient require future imaging or follow-up treatment years later. Because of their tiny size, most patients find the marks are not highly noticeable in daily life.
However, for some cancer survivors, the mark can serve as an unwanted reminder of their cancer journey, potentially leading to psychological distress. Patients concerned about the long-term appearance have options for management after treatment is completed. Like other tattoos, these marks can be faded using laser removal treatments, which are highly effective due to the small amount of ink used. Some institutions also offer alternatives, such as semi-permanent inks or biodegradable markers, which naturally fade over several months.