Irradiation of the heart during tangential breast treatment: a study within the START trial

Radiotherapy to the breast is often given as a component of the treatment for women with breast cancer. It has been shown to increase overall survival although an increase in cardiac mortality has also been noted. This study was undertaken as part of the START trial quality assurance programme to record and evaluate the cardiac dose using modern radiotherapy techniques. Departments randomizing patients into the START trial and who had CT facilities for planning breast patients were invited to take part. 62 patients were included. CT slices were taken at the level of the maximum heart depth and on the treatment field central axis. Each patient was planned in the normal way and the distributions were analysed by the quality assurance team at Mount Vernon Hospital. The maximum heart position was found to be inferior to the central axis used for breast planning for the majority of patients; mean position 2.3 cm inferior with a mean maximum heart depth of 0.55 cm. For 45% of patients the maximum heart dose was less than 50% of the prescribed dose. The study showed that the volume of irradiated cardiac tissue has decreased compared with earlier studies, and also highlighted the need to scan away from the central axis if the dose to cardiac tissue is to be assessed.