What is the optimum breast plan: a study based on the START trial plans

Abstract

Each year thousands of women within the UK are treated with radiotherapy for breast cancer. The majority of these women are treated using a medial and lateral tangential field. This study evaluates the plans submitted to the quality assurance (QA) team of the START trial and investigates some of the differences between departments. Throughout the START trial, hardcopies of the radiotherapy dose distribution on the central slice for one in three women were submitted to the QA team for analysis. The QA team measured physical parameters including breast size and lung depth as well as noting parameters used for the radiotherapy delivery including beam energy, field size and wedge angle. Over 1400 plans from 36 centres were analysed. The mean patient separation was 19.7 cm (SD 2.7 cm) with a mean lung depth of 1.5 cm (SD 0.7 cm). The modal beam energy was 6 MV and the mean wedge angle was 23 degrees . Significant differences in the choice of wedge angle between departments were noted; however, in 90% of cases the resultant plan complied with the maximum dose gradient of 10% on the central axis specified by the trial protocol. Less than 3% (37 plans) had dose gradients of greater than 12%. This resulted in a mean dose gradient for all patients on the central axis of 5.7% (SD 2.9%).