Intra- and Interfractional Variations for Prone Breast Irradiation: An Indication for Image-Guided Radiotherapy

Prone positioning of patients for breast irradiation significantly reduces the uncertainty introduced by intrafractional respiratory motion. The presence of large systematic error in the interfractional variations necessitates a large clinical target volume-to-planning target volume margin and indicates the importance of image guidance for partial breast irradiation in the prone position, particularly using imaging modality capable of identifying the lumpectomy cavity.