| Precision radiotherapy is the development trend of modern radiation oncology andis the advanced technology to improve tumor cure rate with reducing radiotherapy sideeffects or complications. Dose verification in radiotherapy process plays an importantrole to make the plan more accurate and improve the gain ratio of radiotherapy.However, current methods based on transmitted dose-verification are not mature andcan’t achieve three-dimensional real-time dose verification. With the emergence of therunway electron cyclotron MM50and the use of PET imaging in heavy-ion therapyprocess, a new dose verification technique by PET scans is proposed. Athree-dimensional dose verification experiment on energetic photon radiotherapy byPET device was carried out in this study, and the characteristics and dose distribution ofenergetic scanning photon were simulated and measured. The yields of positronemitting radionuclide and positron distribution in each phantom were studiedsystematically; in addition, comparison of positron distribution with dose distributioncalculated by TPS and BEAM program was analyzed to discuss the clinical feasibilityof PET dose verification. The results of this study provided a new way of thinking forclinical precision radiotherapy.Applying Monte Carlo program, the structure model of MM50accelerator headmodule was established and high-energy photon dose distribution in water phantom wassimulated. The simulated results were compared with water tank measurement invarious fields to study the beam characteristics and its dose distributions in water. Theresults showed that uniformity and symmetry of energetic scanned photon were below5%, calculated results had good agreement with the measured.Based on the theory and reaction cross-section of photo-nuclear reaction12C （γ,n）11C and16O（γ, n）15O, hydrogel phantom, poly-ethylene phantom and heterogeneousphantom were made. Then the dose distribution in each phantom was calculated by TPSand Monte Carlo simulation. In different radiation conditions, positron activity distributions scanned by PETwere compared with the dose distributions calculated in each phantom after irradiation.The results showed that: the yields of11C and15O after2Gy of50MV X-ray photonirradiation had reached the level of PET imaging and number of11C and15O generatedby50MV photon were3.86and3.88times the25MV, respectively;3-D dosedistributions were similar with positron distributions in the three phantoms. Besides,small animal and patient cases were carried out and compared with phantomexperiments, which showed PET dose verification of energetic photon radiotherapy isaccurate and feasible. |
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