Fig. 1From: Using field size factors to characterize the in-air fluence of a proton machine with a range shifterSpiral delivery pattern with control points for efficient FSF measurements. The red triangles show the control points used to pause the beam delivery and record the charge. Using the spiral pattern and the control points, a set of FSFs can be obtained by delivering just one beam with the maximum field size (i.e., 20 cm × 20 cm)Back to article page