Objective To investigate the difference of target volumes and dosimetric parameters between supine and prone positions for whole breast irradiation after conserving surgery.~Methods Breast cancer patients with T1-2N0M0 stage who underwent radiation therapy after conserving surgery were enrolled. Supine and Prone scan sets were acquired during free breathing for all patients. Target volumes and organs at risk (OARs) including heart, ipsilateral lung and bilateral breast were contoured by the same radiation oncologist. The tumor bed (TB) was determined based on surgical clips. The Clinical target volume (CTV)consisted of the whole breast. The planning target volume (PTV) was CTV plus 0.5cm. The boost of PTV (PTVboost) was TB plus 0.5cm. Dosimetric parameters of target volumes and OARs were compared between supine and prone position.
Radiotherapy after breast conserving therapy plays an important role in early stage breast cancer patients. It not only results in a reduction in local and regional recurrence but also decrease the death rate effectively. For adjuvant radiotherapy, supine positioning is the most common approach and has multiple advantages. Due to deformability and softness of the breast, during simulation and treatment in supine position, the breast stretches over the chest wall, especially in patients with large and pendulous glands. Thus the organs at risk (OARs) received dose increased. The radiotherapeutic toxicity are unavoidable. Some present studies show that the prone positioning of patients can improve dose homogeneity and reduce the dose distribution in OARs in patients with large and pendulous glands. Chinese women have relatively small breasts, the advantages of those have not been established. Therefore, investigators compared the parameters between supine and prone positions for whole breast irradiation after conserving surgery.