Dosimetric analysis of beam arrangement for intensity-modulated radiation therapy in the postoperative irradiation of thymoma

This study aimed to investigate the dosimetric effect of various beam arrangements (BAs), for intensity modulated radiotherapy (IMRT) in female thymoma patients. Six-field IMRT plans with three different BAs, named IMRTCA, IMRTCS, and IMRTNC were created for each patient. The couch angles of all fields were selected at 0 degrees, which made the fields coplanar in the axial plane in IMRTCA plans. The couch angles of all fields were selected to be 90 degrees, which makes the fields coplanar in the sagittal plane in IMRTCS plans. The couch angles of the four fields and two fields were selected as 90 degrees and 0 degrees, respectively in IMRTNC plans. Plans were compared in terms of dose homogeneity, conformity, and OAR doses. IMRTCS plans created with coplanar beams in the sagittal plane could offer significant advantages in terms of breast and lung sparing. IMRTCS may be useful for young female thymoma patients to reduce the risk of developing a second cancer in the breast. In addition, it should be considered that IMRTCS contributes approximately 1 Gy to the mean heart dose.