Author: Thomas R. Bortfeld, Prof. Elisabetta De Bernardi, Tianxue Du, Beatrice Foglia, Chiara Gianoli, Takamitsu Masuda, Katia Parodi, Marco Pinto, Boon-Keng Kevin Teo, Yunhe Xie 👨🔬
Affiliation: Department Of Radiation Oncology, Massachusetts General Hospital (MGH), School of Medicine and Surgery, University of Milano-Bicocca, Department of Medical Physics, Ludwig-Maximilians-Universität München (LMU Munich), Department of Medical Physics, Ludwig-Maximilians-Universität (LMU) München, National Institutes for Quantum Science and Technology (QST), University of Pennsylvania, Department of Experimental Physics - Medical Physics, Ludwig-Maximilians-Universität (LMU) München 🌍
Purpose: The full potential offered by protons in clinical practice is limited by range uncertainties. One possibility for monitoring is through secondary prompt gammas (PG). PG emission along the penetration path is correlated to the dose, and PG measurements can be used to infer information about the dose distribution.
Methods: Following promising initial investigations in phantoms presented at AAPM2024 meeting, the deconvolution approach[1], the evolutionary algorithm[2-4] and the maximum-likelihood expectation-maximization (MLEM) algorithm[5-6] were investigated in this work for dose reconstruction from PG for clinical cases. These techniques were applied first to simulations (for ideal PG emission in the patient) of a head and neck (H&N) tumour indication, considering two pencil beams delivered to regions with different heterogeneity levels. A systematic analysis depending on PG statistics is ongoing. Extension to PG from emission to detection is in progress, considering 1D PG signals acquired with a knife-edge slit camera[7] during several treatment fractions for two additional brain cancer patients[8-9].
Results: The accuracy of the reconstructed 3D dose distributions was evaluated via γ-index and range analyses with different settings. Regarding dose reconstruction from simulated 3D PG distributions at emission, the γ(2%/2mm) passing rate was found above 97% for every algorithm used. The resulting |ΔR80| between simulated and reconstructed laterally integrated depth-dose profiles was below 1.4 mm. Results of dose reconstruction from experimental data will be presented.
Conclusion: The feasibility of the investigated dose reconstruction techniques applied to simulated 3D PG distributions at emission considering a H&N patient was verified. Since the emission of PG happens in a timescale below nanoseconds, the algorithms are potentially suitable for real-time adaptive particle therapy.
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