A New Technology for Fast Two-Dimensional Detection of Proton Therapy Beams
Micromegas measurement (black points, upper chart) of a proton spread-out Bragg peak (SOBP) delivered using the double-scattered technique. Five individual Bragg peaks can be seen corresponding to the first (most distal) five segments on the modulator wheel. The five Bragg peaks combine to produce a flat SOBP, as shown by the red line, which was obtained by summing the Micromegas signal over three complete wheel rotations. Two regions are highlighted for closer examination: ((b) bottom left) showing the series of pulses generated by the modulator wheel increasing in amplitude as the water depth lowers, effectively moving the detector into the distal falloff region, and ((c) bottom right) showing three wheel rotations at a depth where four Bragg peaks can be discerned both in the datapoints in the top chart and in the pulses in the bottom right.