Photon-counting CT (PCCT) maintained consistent proton range estimation (R80) across different phantom sizes, tissue types, proton beam energies, and imaging doses, whereas dual-energy CT (DECT) became increasingly inaccurate in larger phantoms at reduced radiation dose.
Even at low-dose imaging (CTDIvol 5 mGy), PCCT kept proton range deviations below 0.5 mm, while DECT exhibited visible photon starvation artifacts leading to proton range errors of up to 20.1 mm in the largest phantom.
These findings suggest that PCCT may substantially reduce CT imaging dose in proton therapy planning without compromising treatment accuracy, making it particularly attractive for repeated imaging, adaptive radiotherapy, pediatric imaging, and large patients.
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Figure 1. Visualization of the workflow followed in this study, including CT scanning, VMI generation, SPR estimation using the Hünemohr method (Hünemohr et al 2014), and a proton plan was created on the phantom. Additionally, the three assessments, phantom size-, traversed tissue type-, and proton energy-dependency are shown with the quantification of proton range, defined as the range at the 80% distal fall-off (R80) per proton spot, to assess range differences. Abbreviations: SPR—stopping-power ratio, DECT—dual-energy computed tomography, PCCT—photon-counting CT.
Source:
Lustermans D, Fonseca GP, Vilches-Freixas G, et al. Evaluation of proton range differences in photon-counting and dual-energy computed tomography across imaging doses and anthropomorphic phantom sizes. Physics in Medicine & Biology. 2026;71:065008.
Protocol
Detail | Value |
|---|
Scanner (PCCT) | NAEOTOM Alpha |
Scanner (DECT) | SOMATOM Confidence |
Application | Proton therapy planning |
Phantoms | Anthropomorphic head phantom + 3D-printed abdomen phantoms (XS, M, L, XL) |
Tube voltage (PCCT) | 120 kVp |
Tube voltage (DECT) | 80 / 140 kVp |
CTDIvol [mGy] | 5, 10, 20 |
Detector collimation (PCCT) | 144 × 0.4 mm |
Detector collimation (DECT) | 32 × 0.6 mm |
Pitch | 0.35 |
Slice thickness | 1.0 mm |
Reconstruction kernel | Qr40 |
Iterative reconstruction (PCCT) | QIR strength 3 |
Iterative reconstruction (DECT) | SAFIRE strength 3 |
Virtual monoenergetic images | 70 keV and 180 keV |
Matrix | 768 × 768 (abdomen PCCT); 512 × 512 (head PCCT & DECT) |
Field of view | 500 mm (abdomen), 300 mm (head) |
SPR estimation | Hünemohr method |
Treatment planning | RayStation 2024B, Monte Carlo dose calculation |
Primary endpoint | Proton range (R80) |
Key Results
Parameter | Main finding |
|---|
Low-dose imaging | PCCT maintained stable proton range estimation even at 5 mGy |
Proton range deviation | PCCT <0.5 mm across all phantom sizes and tissue types |
DECT low-dose performance | Range errors increased with phantom size, reaching 20.1 mm in the XL phantom |
Image artifacts | Photon starvation substantially degraded DECT low-dose performance in large phantoms; PCCT avoided these artifacts |
Tissue dependency | PCCT remained stable across beams traversing soft tissue, bowel and bone; DECT errors increased through denser tissues |
Clinical implication | PCCT enables substantial CT dose reduction for proton therapy planning while preserving range accuracy, potentially benefiting adaptive radiotherapy, pediatric imaging, repeated follow-up imaging and obese patients. |
