Even with the collision consideration, the angles that can be safely accessed for head or foot treatment is significantly larger than a hemisphere. One can consider a typical brain treatment where not only the superior angles are accessible, some of the inferior oblique angles are also available by rotating the gantry towards the patient torso while the couch is rotated. It is true that the solid angle for body treatment is more limited such as the left lung treatment shown in Fig
2a. When the source-to-isocenter distance is limited to 100 cm, the feasible angles shown in Fig
2c is limited. However, the accessible non-coplanar beam angles can be expanded by allowing source-to-isocenter distances greater than 100 cm. An example is shown in Fig.
2b using the validated geometrical modeling method described previously [
1]. With the extended distances, approximately 70% of the 4π surfaces are covered for a left lung treatment. Note that a portion of the missing non-coplanar surface is caused by the couch pedestal occlusion.