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Quantitative Comparison of Proton, Helium- and Carbon-Ion Computed Tomography for Ion Therapy Treatment Planning

S Meyer1*, F Kamp2 , A Mairani3,4 , C Belka2,5 , D Carlson6 , C Gianoli1 , K Parodi1,7 , (1) Ludwig-Maximilians-Universitaet Muenchen, Garching b. Muenchen, Bavaria, (2) University Hospital LMU Munich, Munich, Bavaria, (3) Heidelberg Ion Beam Therapy Center, Heidelberg, Baden-Wuerttemberg, (4) Fondazione CNAO, Pavia, Lombardy, (5) German Cancer Consortium, Munich, Bavaria, (6) Yale university School of Medicine, New Haven, CT, (7) Heidelberg University Hospital, Heidelberg, Baden-Wuerttemberg


(Tuesday, 7/31/2018) 11:00 AM - 12:15 PM

Room: Karl Dean Ballroom B1

Purpose: To quantitatively evaluate and compare proton, helium- and carbon-ion computed tomography (CT) for ion therapy treatment planning, in order to mitigate range uncertainty inherent in the conversion of Hounsfield units into relative stopping power (RSP).

Methods: Different ion-CTs were simulated at 2mGy physical dose for an ideal single-particle tracking detector with experimentally validated beam description for two clinical head&neck cases using the FLUKA Monte-Carlo code. RSP images were reconstructed by an iterative algorithm with integrated most-likely-path and total variation superiorization. Proton-beam treatment plans were optimized on the ground truth and recalculated on the ion-CTs. Variations of relative biological effectiveness (RBE) with ion type and energy for the simulated ion-CT scenarios were quantified by coupling the FLUKA-code to the repair-misrepair-fixation model and Monte-Carlo damage simulation algorithm, accounting for cell survival and DNA complex damage.

Results: Helium-CT offered superior image quality in terms of overall reduced RSP error, while carbon-CT showed the highest accuracy for bone and proton-CT for soft/brain tissue. All ion-CTs displayed comparable performances for dose calculation with minor variations in dose-volume histograms. For a 0.5%/0.5mm gamma-evaluation, carbon-CT exhibited 91% passing-rate, increasing to 98% for proton- and helium-CT. Using single field uniform dose, the average range variation was 0.34mm, 0.32mm and 0.54mm underestimation for proton-, helium- and carbon-CT, respectively. In more heterogeneous regions, proton-CT dose calculation resulted in over-range up to 0.8mm. Depending on the radiosensitivity parameters, the predicted mean RBE for cell survival was 0.82-0.85, 0.85-0.89 and 0.97-1.03 for proton-, helium- and carbon-CT, respectively, while only 0.82, 0.84 and 0.95 for double-strand break induction (using a diagnostic 130kVp X-ray spectrum as reference).

Conclusion: Low-dose ion-CT offers sub-millimeter range accuracy for ion therapy treatment planning and possibly reduced radiobiological implications compared to X-ray imaging. The comparison indicates that helium-CT offers the best trade-off between path estimation accuracy and statistics.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the DFG Cluster of Excellence Munich Centre for Advanced Photonics (MAP) and the DFG project Hybride-Bildgebung in Hadrontherapy fuer Adaptive Ionen-Strahlentherapie.


CT, Treatment Planning, RBE


IM- Particle (e.g., proton) CT: General (Most aspects)

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