National Cancer Awareness Day 2025: What is IMRT? Oncologist explains treatment techniques, benefits and risks

Radiation therapy has been a backbone of cancer treatment for decades, but older methods often came at a cost. Healthy tissues could be damaged while tumours were hit, leaving patients to cope with unwanted side effects. Is IMRT, or Intensity-modulated radiation therapy, changing that image?

IMRT allows doctors to deliver higher doses directly to the tumour while limiting radiation to surrounding organs, says Dr Tejinder Kataria, Chairperson, Radiation Oncology, Medanta, Gurugram. "The goal is effective cancer control with fewer side effects, making treatment safer and more precise", he tells Moneycontrol.
Unlike conventional radiation, which treats a broad area, IMRT relies on detailed imaging, computer-guided planning, and fine-tuned delivery. “Every step, from mapping the tumour to daily alignment checks, is designed to maximise accuracy and protect normal tissues.” shares Dr Kataria and explains how IMRT works:

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• Simulation and imaging
  The process begins with a CT scan — sometimes combined with MRI or PET — while the patient lies still using custom supports. These images map the tumour and surrounding organs, forming the foundation of precision treatment.


• Contouring
  The tumour and nearby critical organs are outlined on the scans. “This step is vital,” says Dr. Kataria. “It ensures the radiation hits the target while sparing healthy tissue.”


• Inverse planning
  Clinicians input goals, such as tumour dose and safe limits for organs. Computer algorithms then calculate optimal beam angles and intensity patterns to meet these goals accurately.


• Beam modulation with mlcs
  Multileaf collimators — hundreds of tiny metal leaves — shape each beam and vary its intensity. Beams can come from fixed angles or rotate continuously, allowing highly conformal treatment.


• Image guidance (IGRT)
  Daily imaging confirms tumour position and patient alignment. Adjustments compensate for natural organ movement or minor differences in setup, keeping treatment precise.

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Here’s what IMRT treats
IMRT is particularly valuable when precision matters:

• Head and neck cancers to protect salivary glands and spinal cord


• Prostate cancer to spare bladder and rectum


• Central nervous system tumours


• Pelvic and gynaecologic malignancies


• Thoracic cancers near the heart and oesophagus


• Certain gastrointestinal, liver, and paediatric tumours

Dr. Kataria further shares the benefits and risks:

• Benefits
  Dose can be shaped to maximise tumour control while limiting harm. Organ-sparing reduces long-term side effects, and higher doses can sometimes improve outcomes.


• Potential risks
  Side effects include fatigue, skin irritation, or site-specific symptoms. Rare late effects may involve organ function changes or low-dose exposure to wider areas. Careful planning minimises these risks.

IMRT sessions are short and painless, usually 10–20 minutes daily over several weeks. “Immobilisation keeps patients steady, and imaging checks maintain accuracy. Ongoing monitoring ensures treatment is both safe and effective.” he adds.

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