Optimization of couch angles and number of arcs in non-coplanar VMAT for pituitary adenomas

Non-coplanar VMAT spares critical organs with short delivery time while maintaining PTV coverage. Due to the growth patterns of pituitary adenoma, the beam angle selection step was simplified by finding the optimal couch angles and number of arcs. The 2 clinical cases with difference PTV sizes were selected to study the results of dose distribution between coplanar and non-coplanar techniques. Later, couch angles were varied from 30 degrees to 90 degrees and 270 degrees to 330 degrees with a 15 degrees interval. The numbers of arcs were varied from 3 to 4 arcs. Then, the selected protocol was applied to 5 pituitary adenoma patients. It was found that 90 degrees and 270 degrees couch angle showed the highest scores. However, these beams passed directly through the body, so the second couch angles of 75 degrees and 285 degrees were selected instead. For number of arcs optimization, 3-arc plan and 4-arc plan demonstrated a similar score. However, the 3-arc plan illustrated an obviously shorter treatment time. After the selection was proven to the 5 patients, there were 4 patients who passed the criteria, while 1 patient did not pass the hippocampal planning criteria. In conclusion, the suggested couch angles were 75 degrees and 285 degrees. The optimal number of arcs for pituitary adenoma was 3 arcs.