S1741
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
Aarhus University / Aarhus University Hospital, Aarhus, Denmark. 3 Department of Radiology and Nuclear Medicine, Maastricht University Medical Centre+, Maastricht, Netherlands. 4 Department of Radiation Oncology, LMU University Hospital / LMU Munich, Munich, Germany
Purpose/Objective: Using dual-energy CT (DECT) imaging showed
improvements in proton therapy, as it can decrease proton range uncertainty. However, DECT is not widely adopted yet in clinical workflow as technical variations may restrict certain applications (e.g. field-of-view and temporal separation). Recently, photon-counting CT (PCCT) was introduced clinically, enabling multi-energy CT imaging with a single scan and detector, and offering reduced imaging dose capabilities. Therefore, this study compared proton range differences in DECT and PCCT under varying imaging doses, across anthropomorphic phantom sizes and treatment beam configurations. Material/Methods: CT images of a head phantom (CIRS; 731-HN) and four anthropomorphic 3D-printed abdomen phantoms with removable fat rings (XS, M, L and XL) were acquired on a DECT (Siemens Healthineers; Confidence; 80/140 kVp with pitch respectively 0.35/0.7) and a PCCT (Siemens Healthineers; Naeotom Alpha; 120 kVp). Virtual monoenergetic images (70 and 180 keV) were generated at three dose levels, including CTDIvol,32cm of 20, 10 and 5 mGy. The open-source software AMIGOpy was used for creating stopping-power ratio images which were then imported into RayStation 2024B (RaySearch Laboratories). Treatment plans were created with fictitious tumors using a field with fixed beam energy to assess proton range accuracy across phantom sizes, while additional plans with varied beam angles (passing through different tissues) and energies were used to evaluate angle- and energy-dependencies (Figure 1). From every proton spot, the range, specified as R80 i.e. at the 80% distal dose fall-off, was extracted and range differences between imaging doses (intra- modality) and between modalities at 20 mGy (inter- modality) were quantified.
Results: Intra-modality variations in R80 distributions became more pronounced with increasing phantom size for DECT, whereas R80 was dose-independent for PCCT (Figure 2). The head and XS-phantom for DECT, showed intra-modality median Δ R80 below 0.3 mm, but this increased to 2.3 mm in the M-sized phantom and even further in the larger phantoms (up to 20.9 mm) due to visible imaging artifacts in the low dose scans. In contrast, PCCT maintained deviations below 0.5 mm regardless of the phantom size, beam angle and energy. Furthermore, inter-modality range discrepancies became more pronounced when proton beams traversed high-density tissues or for longer proton paths.
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