S1749
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
confirmed artifact reduction. Low-energy VMIs improved contrast (d ₄₀ keV = 7 > d ₇₀ keV = 6).(iv) Eleven patients with orbital or spinal implants showed consistent artifact reduction on PCCT. Only PCCT (190 keV VMI) avoided HU saturation in peri-implant tissues (Figure 1).
Lobefalo 2 , Leonardo Nicotera 2,4 , Marco Pelizzoli 2 , Giacomo Reggiori 2 , Stefano Tomatis 2 , Ciro Franzese 2,4 , Marta Scorsetti 2,4 , Cristina Lenardi 1,5 , Pietro Mancosu 2,4 1 Department of Physics "Aldo Pontremoli", University of Milan, Milan, Italy. 2 Radiotherapy and Radiosurgery Department, IRCCS Humanitas Research Hospital, Rozzano, Milan, Italy. 3 Radiotherapy Department, Mediterranean Institute of Proton Therapy, Centre Antoine Lacassagne, Nice, France. 4 Department of Biomedical Sciences, Humanitas University, Milan, Italy. 5 Milan Division, National Institute for Nuclear Physics, Milan, Italy Purpose/Objective: Accurate conversion from CT numbers (HU) to stopping-power ratios (SPR) is essential for proton- therapy dose calculation. This conversion relies on a Hounsfield Look-Up Table (HLUT), which links HU values to corresponding SPRs used for range prediction. This study evaluates whether photon- counting CT (PCCT) can reduce range uncertainty and anatomical dependence, with respect to Single Energy CT (SECT) and Dual Energy CT (DECT), by improving HLUT robustness according to EPTN guidelines [1], minimizing metal artifacts, and enabling a single calibration curve valid for both head and body protocols. Material/Methods: Head and body protocols were acquired with SECT, DECT, and PCCT to characterize image quality and calibration accuracy. PCCT and DECT generated virtual monoenergetic images (VMIs, 40–190 keV). The study comprised four phases:(i) Image quality: Catphan 600 and Gammex 467 phantoms assessed noise, spatial resolution, and HU stability.(ii) Calibration: HU–RED (relative elettron density) and HU–SPR (Stopping Power Ratio) curves were derived in MATLAB, and theoretical versus measured SPRs were compared using Mean Error (ME), Mean Absolute Error (MAE), and RMSE.(iii) Metal implant analysis: Titanium screws were imaged in dedicated phantoms to evaluate geometric accuracy using the Dice coefficient, Hausdorff Distance (HD), and Mean Surface Distance (MSD). Soft-tissue contrast was quantified through the detectability index d.(iv) Clinical validation: PCCT and SECT were compared in patients with metallic implants near or within the treatment field. Results: (i) Cortical bone HU = 1344 ± 17 (PCCT), 1394 ± 27 (DECT), 1368 ± 31 (SECT); variation ± 1.3%, ± 1.9%, ± 2.3% respectively (p < 0.05).(ii) RMSE is reported in table 1. PCCT reduced head-to-body SPR variation to 0.4% (vs 0.8% SECT), confirming weaker anatomical dependence and supporting a single HLUT.(iii) Titanium screw dimensions 2.1 × 4.3 mm (PCCT) vs 3.2 × 4.6 mm (SECT) and 2.3 × 4.5 mm (DECT); higher Dice (0.93 ± 0.02) and lower HD/MSD (0.18 ± 0.04 mm)
Table 1
Figure 1 Conclusion: PCCT significantly improves HU stability, beam- hardening correction, and metal-artifact suppression. By enabling statistically supported, size-independent HLUT calibration, PCCT reduces proton-range uncertainty and enhances the robustness of proton- therapy planning.Funding: National Plan for NRRP Complementary Investments, project PNC0000003 – AdvaNced Technologies for Human-centrEd Medicine (ANTHEM).
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