Effect of Application Rotation on Dose Distribution in Accelerated Partial Breast Irradiation

Objective. To investigate the effect of rotation of the strut-adjusted volume implant (SAVI) device on dose distribution in accelerated partial breast irradiation (APBI). Methods. The required dose distribution in high-dose rate (HDR) partial breast irradiation performed with a multi-catheter device (also referred to as an applicator) is achieved by varying the source position and time spent at each position. Rotation of the device about its axis (which coincides with the central catheter) can modify the planned dose distribution. In this study we introduce an analytical model to determine changes in dose coverage of the planning target volume (PTV). In addition, we report rotation-induced variations in dosimetric parameters determined with the help of commercially available software for brachytherapy calculations. Results. Our analysis of seven different cases of APBI indicates that rotation of the HDR applicator in the breast leads to changes in doses to the PTV, skin and lung. The effect of rotation can be particularly significant when the lumpectomy cavity is close (i.e., less then 1 cm separation) to the skin and/or lung. Conclusions. Rotation of the applicator can cause greater than 10% reduction in dose coverage of the target, increased doses to skin and lung even for small angle of rotation (e.g., 30°) in the case when the cavity-to-skin and cavity-to-lung distances are less than 1 cm