Figure 1.

Beam arrangements and isocenter positions for (a) single fixed‐jaw intensity modulated radiotherapy (sF‐IMRT), (b) F‐IMRT, and (c) tangential partial volumetric modulated arc therapy. For F‐IMRT, six fixed‐jaw fields aimed to geometrically cover the left breast (red lines) and the other six (yellow lines) focused on the right breast. The interval angle for the ipsilateral fields was 6–10 degrees. For tangential partial VMAT, two partial arcs, rotating in opposite directions, aimed to geometrically cover primarily either the left (red line) or right (yellow line) breast. Dashed sectors were avoidance areas where the accelerator beam was off while the gantry was rotating.