Image-Guided Radiation Therapy (IGRT): How It Works

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer: What Is Image-Guided Radiation Therapy?

Image-guided radiation therapy (IGRT) is a precise cancer treatment that uses imaging scans, such as X-rays or CT scans, to track a tumor's exact location immediately before and during radiation. Radiation oncologists can adjust the beam in real time for breathing or organ movement. Keeping radiation focused on the tumor protects surrounding healthy tissue and improves treatment outcomes. [1]

What the research says

• Daily image guidance cut late urinary side effects in prostate cancer. In a comparison of 186 men treated with high-dose IGRT (86.4 Gy, with daily correction using implanted markers) and 190 men treated with high-dose IMRT without IGRT, the 3-year likelihood of grade 2 or higher late urinary toxicity was 10.4% versus 20.0% (p = 0.02); high-risk patients also had better biochemical tumor control at 3 years. This was a retrospective comparison (Zelefsky et al., Int J Radiat Oncol Biol Phys, 2012 [2]).

• Image-guided IMRT reduced late bowel toxicity in a randomized trial. In the PARCER trial of 300 women receiving radiation after surgery for cervical cancer, the 3-year rate of grade 2 or higher late gastrointestinal toxicity was 21.1% with image-guided IMRT versus 42.4% with 3D conformal radiation (HR 0.46; 95% CI 0.29–0.73), with no difference in 3-year disease-free survival (76.9% vs 81.2%) (Chopra et al., J Clin Oncol, 2021 [3]).

Overview of IGRT Technology

Image-guided radiation therapy (IGRT) represents a significant advancement in external beam radiation therapy (EBRT). Traditional radiation methods rely on static images taken weeks before treatment, which may not account for subtle daily changes in tumor position. IGRT solves this by integrating imaging equipment directly into the treatment process, allowing for "daily targeting" that ensures the radiation hits its mark every time.

The procedure utilizes a machine known as a linear accelerator (LINAC), which generates high-energy X-ray or photon beams. During a session, the LINAC or a connected imaging device takes scans to confirm the tumor's coordinates. If the tumor has shifted due to internal movements — such as the filling of the bladder or the expansion of the lungs — the care team can immediately redirect the beams.

Common Applications for IGRT

IGRT is particularly effective for treating tumors located in areas of the body prone to movement or those situated near vital organs.

Cancer Type	Why IGRT is Used
Lung Cancer	Tracks tumors that shift with every breath taken by the patient.
Prostate Cancer	Accounts for movement caused by changes in the bladder or rectum.
Brain Cancer	Ensures sub-millimeter precision near critical neurological structures.
Abdominal Cancer	Manages shifts in the liver or pancreas during digestion and respiration.
Head and Neck	Maintains accuracy as patients may experience slight weight or position changes.

The IGRT Procedure: What to Expect

The process begins with a treatment simulation, where the oncology team takes initial scans and uses laser-light measurements to create a personalized map of the patient's anatomy. This data is used to program the LINAC for the actual sessions.

During the treatment itself, the patient lies on a table while the machine rotates around them. The team stops the procedure periodically to take new scans — which may include X-rays, CT, MRI, or ultrasound — and compares them to the simulation images. This "stop-and-check" method ensures that the radiation dose is delivered exactly where it is needed.

Figure 1: IGRT utilizes real-time imaging to adjust radiation beams, ensuring the tumor is targeted even as it moves within the body.

Comparison of Advanced Radiation Techniques

IGRT is often used in conjunction with other precision technologies to provide a comprehensive treatment plan.

Technology	Primary Function	Relationship to IGRT
IMRT	Modulates beam intensity to match tumor shape.	Often combined with IGRT for both shape and position accuracy.
SBRT	Delivers high doses in fewer sessions.	Uses IGRT to ensure the high dose is safely contained within the tumor.
LINAC	The machine that generates radiation beams.	The hardware platform that typically houses IGRT imaging tools.

Benefits and Safety Considerations

The primary benefit of IGRT is its ability to protect healthy tissue. By reducing the "margin of error" required for radiation delivery, doctors can use higher, more effective doses on the tumor without increasing the risk of side effects in neighboring organs.

Figure 2: The IGRT workflow involves simulation, daily imaging, and precise beam adjustment to maximize treatment safety.

Potential Side Effects

While IGRT is highly targeted, patients may still experience side effects related to the radiation itself. These are generally localized to the area being treated.

• Fatigue: A common sense of tiredness throughout the treatment course.

• Skin Changes: Irritation, redness, or itchiness at the entry site of the beams.

• Gastrointestinal Issues: Nausea, vomiting, or diarrhea, particularly for abdominal treatments.

Figure 3: By narrowing the radiation field, IGRT significantly reduces the exposure of healthy surrounding organs to radiation.

Conclusion and Next Steps

Image-guided radiation therapy is a cornerstone of modern cancer care, offering a level of precision that was previously unattainable. By tracking tumors in real-time, IGRT provides patients with a safer and more effective path toward recovery. If you are scheduled for radiation, speak with your oncologist about whether IGRT is the right choice for your specific diagnosis.

Frequently Asked Questions

How long does an IGRT session take?

Most sessions last between 15 and 20 minutes, though complex cases may require up to an hour to complete the necessary imaging and adjustments.

Does the IGRT machine touch my body?

No, the linear accelerator rotates around you and directs energy beams from a distance; no part of the machine makes physical contact with your skin.

Is IGRT more effective than traditional radiation?

IGRT is considered more effective for moving tumors because it ensures the radiation dose actually reaches the target rather than missing it due to body movement.

How often will I receive imaging scans?

In most IGRT protocols, imaging scans are performed daily, immediately before each radiation treatment, and sometimes during the session.

Can IGRT be used for all types of cancer?

While highly versatile, it is most commonly recommended for cancers in the lungs, prostate, brain, and abdomen where movement is a factor.

What is a treatment simulation?

A simulation is a planning session where scans are taken to create a "map" for your treatment; it does not involve the delivery of actual radiation.

Are the side effects of IGRT different from other radiation?

The side effects are similar to other forms of external beam radiation, but IGRT often reduces their severity by sparing more healthy tissue.

Does IGRT use more radiation than standard treatment?

The imaging scans add a very small amount of radiation, but this is typically offset by the increased safety and precision of the overall treatment.

Can I drive myself home after an IGRT session?

Yes, IGRT does not typically require sedation, and most patients are able to drive and resume normal activities immediately after their appointment.

What should I do if I experience skin irritation?

You should notify your radiation oncology team; they can recommend specific creams or treatments to manage skin sensitivity during your course of therapy.

How do I prepare for image-guided radiation therapy?

Your radiation oncologist explains what happens before, during and after treatment. [1] Before your first session, you have a simulation, a planning session in which your team makes your treatment plan. [1]

When should I call my doctor during or after IGRT?

Common side effects include diarrhea, fatigue, nausea, vomiting and skin irritation or itchiness. [1] Contact your provider if side effects don't go away when you expected or are more severe than you expected. [1]

Does image-guided radiation therapy hurt?

External radiotherapy treatment usually takes only a few minutes and is completely painless, though you need to keep as still as possible throughout. [4]

Related Reading

Precision Cancer Care: Understanding Intensity-Modulated Radiation Therapy (IMRT) explains how shaped, varying beams spare healthy tissue near tumors.

Stereotactic Body Radiation Therapy (SBRT): What It Is, How It Works and What to Expect describes high-dose, few-session radiation that relies on precise imaging.

3D Conformal Radiation Therapy (3D-CRT): Precision Planning for Cancer Treatment explains how 3D imaging shapes radiation beams to the tumor.

External Beam Radiation Therapy (EBRT): Types and What to Expect covers the main type of radiation delivered from a machine outside the body.

References

1. Cleveland Clinic. Image-guided radiation therapy (IGRT). Cleveland Clinic. Last updated February 6, 2024. https://my.clevelandclinic.org/health/procedures/image-guided-radiation-therapy-igrt

2. Zelefsky MJ, Kollmeier M, Cox B, et al. Improved clinical outcomes with high-dose image guided radiotherapy compared with non-IGRT for the treatment of clinically localized prostate cancer. Int J Radiat Oncol Biol Phys. 2012;84(1):125-129. PMID 22330997. https://doi.org/10.1016/j.ijrobp.2011.11.047

3. Chopra S, Gupta S, Kannan S, et al. Late toxicity after adjuvant conventional radiation versus image-guided intensity-modulated radiotherapy for cervical cancer (PARCER): a randomized controlled trial. J Clin Oncol. 2021;39(33):3682-3692. PMID 34506246. https://doi.org/10.1200/JCO.20.02530

4. NHS. What happens during radiotherapy. NHS. Last reviewed June 5, 2023. https://www.nhs.uk/tests-and-treatments/radiotherapy/what-happens/

Medical disclaimer

This article is for general informational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional about any medical condition.