Introduction: The End of Tattoos in Radiation Therapy?
For decades, skin tattoos have been the standard method for positioning patients before each radiation therapy session. These small permanent marks, while functional, represent a physical and psychological burden that many cancer survivors would rather avoid. With the evolution of surface-guided radiation therapy technology — known as SGRT (Surface-Guided Radiation Therapy) — this reality is changing rapidly.
Systems such as AlignRT by VisionRT now enable completely tattoo-free treatments with sub-millimetre accuracy and real-time monitoring. In this article, we explore how SGRT works, the limitations of traditional tattoos, and why radiation therapy centres worldwide are adopting this technology.
What Is SGRT — Surface-Guided Radiation Therapy
SGRT is an external beam radiation therapy technique that uses 3D camera technology to capture the patient’s body surface topography in real time. Instead of relying on isolated skin marks, the system compares thousands of points on the patient’s surface with a reference surface generated from the planning computed tomography (CT) scan.
This approach provides positional information in six degrees of freedom (6DoF) — three translations (vertical, longitudinal, lateral) and three rotations (pitch, roll, yaw) — enabling a more complete and precise alignment than conventional methods based on three tattoo points.
SGRT uses non-ionising structured light, meaning it adds no radiation dose to the patient during the positioning and monitoring process.
How AlignRT by VisionRT Works
AlignRT is the market-leading SGRT system, developed by VisionRT — the pioneer of this technology with over 3,000 systems in clinical use worldwide. It is installed in 24 of the top 25 cancer hospitals in the United States, according to the U.S. News & World Report ranking.
System Architecture
AlignRT uses three ceiling-mounted stereoscopic camera pods in the treatment room — two lateral and one frontal. Each pod contains a structured light projector and two camera sensors that together reconstruct a 3D surface of the patient with a wide field of view (approximately 1 metre).
How It Works
- Reference: During the simulation CT, a reference surface is created from the external body contour. This surface represents the ideal treatment position.
- Positioning: In the treatment room, AlignRT projects light onto the patient’s skin and the cameras capture the surface in real time. The software continuously compares this surface to the reference, providing deviations in 6DoF.
- Correction: Radiation therapists adjust the patient’s position based on quantitative data from the system, including postural corrections that are impossible with tattoos alone.
- Intrafraction monitoring: Throughout the entire treatment, AlignRT continuously monitors the patient’s position. If the patient moves beyond a pre-defined tolerance, the system automatically signals the linear accelerator to pause the radiation beam.
Accuracy and Capabilities
AlignRT delivers tracking accuracy of ≤0.5 mm / ≤0.2° across all couch positions and gantry angles, working with all skin tones. It includes built-in tools such as Postural Video (multi-angle real-time visualisation), surface deformation mapping, and automatic SSD verification.
Traditional Tattoos in Radiation Therapy: Limitations
The conventional positioning method typically uses 3 to 5 small permanent tattoos (ink dots) placed on the patient’s skin during the simulation session. In the treatment room, therapists align reference lasers with these points to position the patient.
Technical Limitations
- Limited positional information: Three isolated points are insufficient to accurately determine position in 6 degrees of freedom. Rotational errors can go undetected.
- Skin elasticity: Tattoo positions can shift with skin mobility, introducing positioning uncertainties. Therapists frequently need to manipulate the skin to align tattoos with lasers.
- No monitoring during treatment: Tattoos are used only for initial positioning. They provide no information about patient movement during beam delivery.
- Confusion with previous treatments: Patients with multiple treatment courses may have several tattoos, making it difficult to identify the correct marks.
- Variable visibility: On darker skin tones, tattoos can be difficult to identify.
Psychological Impact
The scientific literature extensively documents the negative impact of radiation therapy tattoos on patient quality of life. A study published in The Breast Journal, which surveyed breast cancer survivors, found that 70% of patients reported negative feelings about radiation therapy tattoos, viewing them as permanent, unwanted reminders of their diagnosis and treatment. Approximately 80% of respondents stated they would choose a tattoo-free alternative, even if it required additional effort.
Advantages of SGRT with AlignRT Over Tattoos
1. Greater Positioning Accuracy
A systematic review published in 2022, analysing 13 studies on breast radiotherapy, concluded that SGRT consistently improves positioning accuracy and reproducibility compared to tattoos. Mean systematic errors with tattoos ranged from 2.2 to 4.4 mm, while SGRT reduced these to below 2 mm in most cases. 3D displacement vectors were reduced by up to 57% with SGRT.
A Cleveland Clinic study demonstrated a significant reduction in residual positioning errors: 4.0 ± 2.3 mm with SGRT versus 8.3 ± 3.8 mm with tattoos (p = 0.02).
2. Real-Time Monitoring
Unlike tattoos, which only assist with initial positioning, AlignRT continuously monitors the patient’s position throughout the entire session. If movement occurs — a cough, an involuntary shift — the system detects it immediately and can automatically pause the radiation beam. This capability is critical for techniques such as SBRT/SABR and stereotactic radiosurgery (SRS), where high doses are delivered in few fractions.
3. Faster Treatments
Studies show that AlignRT can reduce treatment time by an average of 22% per fraction compared to traditional methods. One study directly comparing both methods reported a reduction in setup time from 11 to 6 minutes. Another, focused on free-breathing breast radiotherapy, demonstrated that SGRT setup was 23 seconds faster per fraction.
4. Tattoo Elimination — Mark-Free Treatments
Over 340 clinical centres worldwide now offer completely tattoo-free treatments thanks to AlignRT. This approach eliminates not only the permanent marks but also the pain of the tattooing procedure and the associated emotional distress. Studies demonstrate that SGRT positioning is equivalent or superior to tattoo-based positioning, validating the safety of this transition.
5. Reduced Verification Imaging
The strong correlation between the surface captured by SGRT and internal anatomy, as verified by image guidance (IGRT), allows in many cases a reduction in the frequency of verification radiographic examinations during the treatment course. This translates to less additional radiation dose for the patient and greater clinical workflow efficiency.
6. Advanced Respiratory Management
AlignRT integrates with Deep Inspiration Breath Hold (DIBH) techniques, particularly important in left breast cancer treatment to protect the heart. The system monitors breathing and ensures radiation is delivered only when the patient is in the correct inspiration position with sub-millimetre accuracy. The Real Time Coach module provides visual feedback to the patient to facilitate cooperation during treatment.
Clinical Applications of SGRT
Although SGRT was initially most widely used in breast radiotherapy, the technology is now applied across virtually all anatomical sites:
- Breast and chest wall: Tattoo-free setup, DIBH for cardiac protection, APBI (accelerated partial breast irradiation)
- Brain: Frameless stereotactic radiosurgery (SRS), enabling open masks and greater comfort
- Lung: SBRT/SABR with respiratory motion management
- Head and neck: Improved positioning with rotational error detection
- Pelvis and prostate: IGRT complement with surface monitoring
- Paediatrics: Potential to reduce the need for anaesthesia in children through non-invasive monitoring
VisionRT also offers complementary solutions such as DoseRT (real-time dose visualisation via Cherenkov imaging) and AlignRT InBore for in-bore monitoring with modern treatment systems.
FAQ — Frequently Asked Questions About SGRT
What is SGRT and how does it differ from traditional tattoos?
SGRT (Surface-Guided Radiation Therapy) is a technology that uses 3D cameras to position and monitor patients during radiation therapy, comparing thousands of points on the body surface with a digital reference. Unlike tattoos, which provide only 3 to 5 fixed reference points, SGRT delivers continuous information in six degrees of freedom with monitoring throughout the entire treatment.
Is SGRT as accurate as tattoos for positioning?
Clinical studies consistently demonstrate that SGRT is equal to or better than tattoos in terms of positioning accuracy. Systematic reviews show reductions in setup errors of up to 50% with SGRT, with systematic errors typically below 2 mm. AlignRT tracking accuracy is ≤0.5 mm.
What are the advantages of SGRT for patients?
Key advantages include the elimination of permanent tattoos (reducing psychological impact), faster treatments, greater comfort during sessions, and continuous monitoring that ensures safety even if the patient moves involuntarily during treatment.
Can AlignRT be used for all cancer types?
Yes. Although initial use was predominantly in breast cancer, AlignRT is now used across virtually all sites — including brain (SRS), lung (SBRT), head and neck, pelvis, prostate, and paediatrics. Over 3,000 systems are in clinical use worldwide.
Does Interphysix provide SGRT solutions?
Yes. Interphysix is the official VisionRT distributor in Portugal, offering the full portfolio of SGRT solutions including AlignRT, SimRT, DoseRT and complementary modules, with local technical support and specialised training.
Conclusion
Surface-guided radiation therapy represents a significant evolution in patient positioning and monitoring for radiation therapy. The scientific evidence — with over 300 peer-reviewed articles published — consistently supports that SGRT with AlignRT offers accuracy equal to or better than traditional tattoos, with additional benefits in speed, safety, respiratory management, and patient experience.
For radiation therapy centres looking to improve treatment quality and patient well-being, the transition to tattoo-free treatments with SGRT is not only feasible — it is increasingly the global standard of care.
To learn more about implementing SGRT at your centre, contact Interphysix — the official VisionRT distributor in Portugal.
Última actualização: 20/03/2026