Optimal gantry angles and field sizes in kilovoltage cone-beam tomosynthesis for set-up of women with breast cancer undergoing radiotherapy treatment.

Optimal beam geometry for kilovoltage cone-beam tomosynthesis (CB-TS) imaging for the set-up of 20 patients with breast cancer was analyzed and presented for prone and supine scenarios. Gantry angles and field sizes that allow maximum clearance and minimum dose to normal organs from kilovoltage imaging were determined for medial and lateral arcs. Optimal CB-TS arc span may vary depending on patient geometry, particularly on the separation between the cavity and the chest wall. CB-TS arc angles 40 degrees were found to be optimal for the cavity to chest wall separation d>3 cm for supine set-up and d>7 cm for prone set-up. Maximum required jaw openings were 20 x 14 cm(2). Recommendations are provided for clinical implementation of CB-TS imaging for breast cancer patients.