 Around 20 of women who receive breast radiotherapy RT experience moderate to severe breast hardening and shrinkage. These side-effects have been shown to be important factors influencing quality of life after breast radiotherapy. It is thought that the likelihood of developing these side-effects is related to the presence of underlying genetic differences in patients. In order to identify these genetic differences, the severity of side-effects needs to be accurately measured. Currently, clinical assessments are conducted by a clinician but this is not specific enough to be able to relate development of breast shrinkage and hardening to genetic differences. For example, clinical assessment often fails to distinguish between hardness due to swelling known as oedema and hardness due to generalised radiation-induced scarring known as fibrosis. Ultrasound techniques, however, may be able to help quantify and characterise radiotherapy-associated changes in breast tissue allowing for better correlation with genetic abnormalities. Once genetic changes can be identified, adjustment of breast RT treatments or add drugs to help reduce side-effects in women at higher genetic risk of side-effects may be possible. 