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Positron emission tomography for quality assurance in proton therapy

PhD ceremony:Mr H.J.T. (Tom) Buitenhuis
When:January 10, 2020
Start:16:15
Supervisor:dr. S. (Sytze) Brandenburg
Co-supervisor:P.G. (Peter) Dendooven
Where:Academy building RUG
Faculty:Medical Sciences / UMCG
Positron emission tomography for quality assurance in proton
therapy

To verify the dose delivery of proton therapy for cancer irradiation, secondary signals need to be measured since the protons stop at the end of their range inside the patient. The most-often used techniques currently are positron emission tomography (PET) and prompt gamma-ray imaging. PET is the oldest method used to verify the dose delivery from proton therapy, but its disadvantage is the delayed feedback due to the half-life of the radioactive decay. Imaging of nuclides with a short half-life can overcome this obstacle.

In this thesis, imaging of the most-promising short-lived nuclides is investigated. The results of a proof-of-principle experiment of beam-on PET imaging of short-lived 12-N nuclei are presented. A method was developed to subtract the long-lived background signal from the 12-N image by introducing a beam-off period into the cyclotron beam time structure. This allows the isolation of the 12-N contribution. A range shift of 5 mm was measured as 6 +- 3 mm using the 1D 12-N profile. A simulation shows that a large dual-panel scanner that images a single spot at the beginning of the dose delivery, can measure a 5 mm range shift with millimeter accuracy.

A series of clinically realistic simulation studies were performed to investigate the high-level choices that arise when considering a dose delivery verification system. Based on the simulation of the production of prompt gamma-ray and positron-emitting nuclides, no imaging modality and protocol can be recommended that will produce the best information on the deviations with respect to the treatment plan for all situations.