What is the difference between IMRT, IGRT, SBRT, and SRS, and how do I know which one I need?

IMRT, IGRT, SBRT, and SRS are acronyms for different radiation delivery techniques, and patients encounter them all at various points in a cancer diagnosis and treatment journey. Let me explain each one and why the distinctions matter for treatment selection at SPARSH Hospital, Hennur Road, Bengaluru. IMRT, or Intensity Modulated Radiotherapy, refers to the shaping of the radiation dose to conform closely to the three-dimensional outline of the tumour while limiting the dose received by surrounding normal tissues. The radiation beam is divided into multiple small beamlets whose individual intensities are modulated by a computer-optimised plan to produce a dose distribution that treats the tumour adequately while sparing the organs at risk. It is now the standard technique for most cancer types, including breast cancer, cervical cancer, and prostate cancer. IGRT, or Image Guided Radiotherapy, refers to the use of imaging at the treatment machine, typically a cone-beam CT or surface guidance system, to verify that the patient is positioned exactly as planned immediately before each fraction is delivered. It is used in combination with IMRT rather than as an alternative to it: IMRT shapes the dose, IGRT verifies the position. Together, IMRT and IGRT produce the standard of precision radiation delivery at SPARSH Hospital. SBRT, or Stereotactic Body Radiotherapy, and SRS, or Stereotactic Radiosurgery, both refer to techniques that deliver very high doses of radiation to precisely defined, relatively small targets in a small number of fractions. The distinction is anatomical: SRS is the term used when the target is in the brain, and SBRT is used for targets elsewhere in the body, including lung, liver, spine, adrenal gland, and other sites. Both require extremely precise patient positioning and very accurate tumour targeting because the high dose per fraction means that any geographic miss has a significant consequence. The specific technique used for any individual patient is determined by the cancer type, the size and location of the tumour, the proximity to critical structures, and the clinical intent of treatment, and this determination is part of the treatment planning process at my clinic.
Written by Dr. P Sasikala, MBBS, DMRT, DNB (Radiation Oncology), Best Paper Award (Indian Brachytherapy Society, 2016), Karnataka Leadership Award, Consultant Radiation Oncologist, SPARSH Hospital, Hennur Road, HBR Layout, Bengaluru 560043. Monday to Saturday, 9:00 AM to 5:00 PM. Phone: +91 80958 09322.
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