Homogeneity index in radiotherapy

Radiotherapy planning aims to place an effective dose within the tumour or target while limiting exposure to nearby healthy structures. The homogeneity index compares dose levels across the target, so it can show whether some areas receive more or less radiation than intended. The exact formula and preferred range vary between planning systems and treatment sites. It is one part of plan evaluation, alongside target coverage, organs at risk, treatment technique and the clinical purpose of treatment. It is not a diagnosis and does not predict an individual outcome by itself.

If this term appears in your treatment plan, ask the radiation oncologist or medical physicist which definition is being used and what the result means for your target. Ask whether the plan adequately covers the intended area and how nearby organs are protected. Do not compare a value from one person, machine or cancer site with another. Planning may be adjusted for cancers such as breast, brain, cervical, bowel, head and neck, skin or womb cancer when the clinical team believes a different distribution better balances treatment aims and safety.

The index itself does not create symptoms or require emergency action. Contact your radiotherapy team promptly if you develop severe or rapidly worsening pain, new neurological changes, breathing difficulty, inability to swallow fluids, uncontrolled bleeding, or a high fever during treatment. Report new symptoms early because they may relate to the treated area, another illness or a medicine, rather than to the homogeneity index.

What formula was used for my homogeneity index? How does my value relate to target coverage and nearby organs? Are there dose areas you are deliberately protecting or accepting? Would another planning approach change the balance between coverage and normal-tissue exposure?