Dosimetric study of beam angle optimization in intensity-modulated radiation therapy planning.

PURPOSE: The quality of intensity-modulated radiotherapy (IMRT) highly depends on the choice of beam orientations and optimization algorithms used in the treatment planning. The present work reports dosimetric study of IMRT plans generated using preselected equiangular beam orientations (PSBO) and beam angle optimization (BAO) for the patients of prostate, head and neck, and esophagus carcinoma.

MATERIALS AND METHODS: The computed tomography (CT) datasets of 30 patients treated with IMRT for prostate, head and neck, and esophagus carcinoma were selected. Two IMRT plans were made for each patient. First plan was prepared for seven to nine fields PSBO in coplanar arrangement. The second plan was made using the BAO by a computerized algorithm compatible treatment planning system (TPS). The dose-volume histograms (DVHs) of PSBO and BAO plans were compared for all the patients. The treatment plans were compared using the parameters delivered monitor units (MUs), doses delivered to organs at risk (OARs), target coverage (conformity index (CI)), homogeneity index (HI), and quality index (QI).

RESULTS: DVHs generated showed that OARs receive almost identical or slightly better doses in case of BAO as compared to PSBO. CI, HI, and QI values were almost same for two plans. However, we have noticed significant reduction in MUs for all the plans generated using BAO.

CONCLUSIONS: It is concluded that BAO provides superior plan with respect to MUs and should be used whenever possible in IMRT planning.