Double-Field Hadrontherapy Treatment Monitoring With the INSIDE In-Beam PET Scanner: Proof of Concept

Positron emission tomography (PET) is a well established imaging technique for range monitoring in hadrontherapy. Multiple fields are standard protocol in treatments, but because of washout and residual activity background from previous irradiation plans, to this date quantitative verification of the particle range for each beam field is still an open issue. In this paper, a new method for the evaluation with a PET detector of the activity range of the second field of a treatment is discussed. Two treatment plans with two parallel-opposed beam fields, one using protons and one using carbon ions, were delivered on PMMA phantoms. In both cases, the second beam field was extracted from the first irradiation residual activity and compared with a reference image, obtained from the experimental acquisition of the second field alone. Results demonstrate good agreement between the extracted second field and the reference image, with average difference in the activity range along the preferential direction of the beam less than 0.5 mm for protons, and 1.5 mm for carbon ions. Without taking into account any preferential direction, differences within 0.5 mm were found for both cases. The method will soon be tested with nonhomogeneous phantoms and, subsequently, with in-vivo clinical data.