Speaker
Description
Introduction: Due to steep dose gradients of the Bragg peak, proton and ion beam therapy is more sensitive to treatment uncertainties compared to conventional radiotherapy. With overall range uncertainty of ~3 – 5%, ensuring robustness of treatment delivery reduces dose conformality – hindering full potential of these modalities.
Apart from conventional strategies, range verification methods could be used: Bragg peak localization via detection of secondary particles or dedicated anatomical imaging for relative stopping power evaluation. Such approaches could enable proper range assessment before and during treatment, delivered dose verification in-vivo and real-time identification of unexpected delivery inaccuracies - crucial in hypofractionation and novel modalities as FLASH therapy.
With helium ion therapy as promising future modality, studies on specifically adapted range verification methods are lacking, though would be beneficial for implementation in technical designs of dedicated delivery systems.
Aim of the Work: To investigate and quantitatively evaluate methods for range verification to ensure required precision and accuracy in high dose helium ion therapy by anatomical imaging or Bragg peak localization.
Methods: Presented work is based on Monte Carlo simulations performed in Geant4 (v. 11.0.1.), using computational resources of RTU High Performance Computing centre. Following range verification methods were quantitatively evaluated, considering technical design parameters of CERN NIMMS HeLICS synchrotron: high energy proton radiography, helium-3 ion radiography, mixed helium-deuteron beam radiography, positron emission tomography-based verification and prompt gamma photon signal enhancement by 18O contrast agent.
Several image quality metrics (spatial resolution, CNR, imaging dose, WEPL accuracy and others) were quantitatively evaluated for the radiography modalities. For Bragg peak localization methods, correlation with absorbed dose distribution, achievable range sensitivity and impact of primary beam intensity was assessed.
Results and Conclusions: For pre-treatment patient position verification, helium-3 ion radiography and 330 – 500 MeV proton radiography would enable sufficient image quality for full-body imaging.
Mixed helium-deuteron beams with fluence ratio 1:100 could be used for range monitoring, while 1:10 – for 2-dimensional imaging during treatment delivery.
Direct Bragg peak localization in helium-4 ion therapy could be feasible via detection of unique fluorine-17 and fluorine-18 beta(+) decay patterns. Another approach could be prompt gamma photon signal enhancement by 18O contrast agent – increased emission yields and unique spectral lines for spectroscopic monitoring.
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