Systematic analysis on the achievable accuracy of PT-PET through automated evaluation techniques

Particle Therapy Positron Emission Tomography (PT-PET) is currently the only clinically applied method for in vivo verification of ion-beam radiotherapy during or close in time to the treatment. Since a direct deduction of the delivered dose from the measured activity is not feasible, images are compared to a reference distribution. The achievable accuracy of two image analysis approaches was investigated by means of reproducible phantom benchmark tests. This is an objective method that excludes patient related factors of influence.

Two types of phantoms were designed to produce well defined deviations in the activity distributions. Pure range differences were simulated using the first phantom type while the other emulated cavity structures. The phantoms were irradiated with (12)C-ions. PT-PET measurements were performed by means of a camera system installed at the beamline. Different measurement time scenarios were investigated, assuming a PET scanner directly at the irradiation site or placed within the treatment room. The images were analyzed by means of the Pearson Correlation Coefficient (PCC) and a range calculation algorithm combined with a dedicated cavity filling detection method.

Range differences could be measured with an error of less than 2 mm. The range comparison algorithm yielded slightly better results than the PCC method. The filling of a cavity structure could be safely detected if its inner diameter was at least 5 mm.

Both approaches evaluate the PT-PET data in an objective way and deliver promising results for in-beam and in-room PET for clinical realistic dose rates.