IGRT — Image-Guided Radiation Therapy Explained

Image-guided radiation therapy is a sophisticated radiation delivery platform that integrates imaging technology directly onto or within the linear accelerator treatment machine. Because internal organs naturally shift, expand, or contract between appointments—due to breathing, digestion, bladder filling, or patient weight changes—tumour locations are dynamic rather than fixed.

IGRT resolves this challenge by capturing two- or three-dimensional images, such as cone-beam computed tomography (CBCT), planar X-rays, or magnetic resonance imaging (MRI), immediately before administering the beam. Computer software compares these real-time images against baseline simulation scans, allowing radiation therapists to make micro-adjustments to the treatment couch or beam angles before treatment begins.

Precision is paramount in modern radiation oncology. By verifying the exact coordinates of the tumour every single day, IGRT permits radiation oncologists to shrink safety margins around the target. This reduction dramatically lowers the radiation exposure to surrounding healthy organs, minimising both immediate side effects and permanent complications. It also allows doctors to safely escalate the radiation dose to the tumour, improving the likelihood of successful treatment.

While not reliant on laboratory biomarkers, IGRT often uses physical markers. Small radiopaque gold seeds or metallic clips, known as fiducial markers, are sometimes implanted into or near the tumour prior to treatment planning. During each treatment session, these markers show up clearly on imaging, serving as precise internal landmarks.

IGRT is invaluable for tumours situated within or near movable organs. It is routinely used in treating prostate cancer, lung cancer, liver cancer, gynaecological malignancies, bladder cancer, gastrointestinal tumours, and head and neck cancers situated near vital structures like the spinal cord or salivary glands.

IGRT is rarely used in isolation; it is the guiding mechanism for other advanced radiotherapy techniques, such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiotherapy (SBRT). By ensuring accurate targeting, IGRT makes it possible to safely combine intense radiotherapy with concurrent systemic treatments like chemotherapy or immunotherapy.