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Phys Med Biol. 2019 Mar 14. doi: 10.1088/1361-6560/ab0fdf. [Epub ahead of print]

Dosimetric accuracy and radiobiological implications of ion computed tomography for proton therapy treatment planning.

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Department of Medical Physics, Ludwig-Maximilians-Universitaet Muenchen, Am Coulombwall 1, Garching b. München, Bavaria, 85748, GERMANY.
Radiotherapy, Klinikum der Universitat Munchen, Marchioninistraße 15, Munich, 81377, GERMANY.
Radiation Oncology, UniversitatsKlinikum Heidelberg, Heidelberg, 69120, GERMANY.
Medical Physics, Fondazione CNAO, Via Strada Privata Campeggi snc, 27100, Pavia, ITALY.
Department of Radiation Oncology, University Hospital of Ludwig-Maximilians-University Munich, Munich, GERMANY.
Department of Therapeutic Radiology, Yale University School of Medicine, PO Box 208040, New Haven, Connecticut, 06520-8040, UNITED STATES.
Ludwig-Maximilians-Universität München, Munich, GERMANY.
Experimental Physics Medical Physics, Ludwig-Maximilians-Universitaet Muenchen, Am Coulombwall 1, 85748 Garching b Munchen, Munich, GERMANY.


Ion computed tomography (iCT) represents a potential replacement for X-ray CT (xCT) in ion therapy treatment planning to reduce range uncertainties, inherent in the semi-empirical conversion of xCT information into relative stopping power (RSP). In this work, we aim at quantifying the increase in dosimetric accuracy associated with using proton-, helium- and carbon-iCT compared to conventional xCT for clinical scenarios in proton therapy. Three cases imaged with active beam-delivery using an ideal single-particle-tracking detector were investigated using FLUKA Monte-Carlo simulations. The RSP accuracy of the iCTs was evaluated against the ground truth at similar physical dose. Next, the resulting dosimetric accuracy was investigated by using the RSP images as patient model in proton therapy treatment planning, in comparison to common uncertainties associated to xCT. Finally, changes in relative biological effectiveness (RBE) with iCT particle type/spectrum were investigated by incorporating the repair-misrepair-fixation (RMF) model into FLUKA, to enable first insights on the associated biological imaging dose. Helium-CT provided the lowest overall RSP error, whereas carbon-CT offered the highest accuracy for bone and proton-CT for soft tissue. For a single field, the average relative proton beam-range variation was -1.00%, +0.09%, -0.08% and -0.35% for xCT, proton-, helium- and carbon-iCT, respectively. Using a 0.5%/0.5mm gamma-evaluation, all iCTs offered comparable accuracy with better than 99% passing-rate, compared to 83% for xCT. The RMF model predictions for RBE for cell death relative to a diagnostic X-ray CT spectrum were 0.82-0.85, 0.85-0.89 and 0.97-1.03 for proton-, helium-, and carbon-iCT, respectively. The corresponding RBE for DNA double-strand break induction was generally below one. iCT offers great clinical potential for proton therapy treatment planning by providing superior dose calculation accuracy as well as lower physical and potentially biological dose exposure compared to xCT. For the investigated dose level and ideal detector, proton-CT and helium-CT yielded the best performance.


carbon computed tomography; dose calculation; helium computed tomography; ion computed tomography; proton computed tomography; proton therapy; repair-misrepair-fixation (RMF) model


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