On‐line monitoring and PET imaging of the positron‐emitting activity created in tissue by proton radiotherapy beams

Abstract

An imaging system was designed and tested to monitor the positron‐emitting activity distribution created by proton radiotherapy beams during treatments. Decay data were acquired and imaged between beam pulses and after irradiation. The range of a 150 MeV proton beam may be verified after a single beam pulse to within the resolution of the imaging system, which was 1.2 cm. Over 80% of the initial positron‐emitting activity is from while the remainder is primarily with traces of and The dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. In some situations the width of the plateau region of a Spread‐Out Bragg Peak may be inferred from the fall of activity at the distal end of the distribution. Radioisotopic imaging may also be performed along the beam path by fitting decay data collected after the treatment is complete. Using this technique, it is shown that variations in elemental composition in inhomogeneous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals that is created well beyond the Bragg peak, apparently by secondary neutrons.