ESTRO 2023 - Abstract Book

S1541

Digital Posters

ESTRO 2023

B. Foglia 1 , C. Gianoli 1 , T. Masuda 2 , T. Bortfeld 3 , J. Verburg 3 , K. Parodi 1 , M. Pinto 1

1 Ludwig-Maximilians-Universität (LMU), Experimental Physics - Medical Physics, Garching bei München, Germany; 2 National Institutes for Quantum Science and Technology, -, Chiba, Japan; 3 Massachusetts General Hospital (MGH), Radiation Oncology, Boston, USA Purpose or Objective Clinical exploitation of the favourable characteristics of protons in cancer therapy is limited by a high sensitivity to range uncertainties. The distribution of prompt-gamma (PG), emitted after nuclear interactions of protons with tissue, could be used for in vivo verification. The most desirable comparison in terms of dose distribution requires dose reconstruction. This work aims at tackling the reconstruction of the actual delivered dose from the PG signal. Materials and Methods Different strategies have already been proposed to reconstruct the dose from a distribution of detected secondary particles, mostly positron emitters (PE). Among them, very promising investigated methods are the analytical deconvolution[1], the evolutionary algorithm[2][3] and the ML-EM algorithm[4][5]. These techniques are based on the forward filtering approach, firstly developed by Parodi and Bortfeld[6] for PET monitoring and recently extended to PG monitoring by Pinto et al.[7] The methods were mostly applied to PE distributions. Only the evolutionary algorithm has been applied on PG distributions so far, and only on homogeneous targets[2]. Within this work, the feasibility of the application of the mentioned techniques to PG distributions was assessed with simulations of protons interacting with homogeneous (fig.1) and inhomogeneous (slab) phantoms (fig.2). The accuracy of the reconstructed curves from simulations were evaluated according to different metrics. A first step towards comparison to measured data has been made with the irradiation of a head phantom at the Francis H. Burr Proton Therapy Center (MGH, Boston, USA), where PG data were acquired with a PG spectroscopy detector prototype[8].

Results For all the methods applied to simulations to the homogeneous case, the γ (3%/3mm) passing rate is always around or above 90%; at other thresholds (2%/2mm, 1%/1mm) is more than 80%. The Δ R ₈₀ , absolute difference between the positions of the 80% of the dose maximum in the distal fall-off for the simulated and reconstructed curves, is always less than 0.5 mm. The