Commissioning a Novel Single Photon Counting CT Simulator for Radiotherapy Planning
Abstract
Purpose
Single-photon counting computed tomography (SPCCT) offers distinct advantages over conventional CT through energy-resolved measurements, enhanced spatial resolution, and improved soft-tissue contrast. While SPCCT demonstrates utility in diagnostic imaging, its application as a radiotherapy simulator remains unexplored. We evaluated the Siemens NAEOTOM Alpha SPCCT scanner's suitability for radiotherapy simulation by assessing geometric accuracy, image quality, dosimetric performance, and relative electron density calibration.
Methods
Commissioning followed the AAPM Task Group 66 guidelines, including electromechanical evaluation, image-quality assessment, and radiation-safety verification. The CATPHAN 604 phantom evaluated CT number accuracy, uniformity, spatial resolution, low contrast detectability, and geometric accuracy across clinical protocols. Dosimetric measurements utilized CTDI phantoms with a 100-mm pencil ion chamber. Relative electron density (RED) calibration employed an Advanced Electron Density phantom at selected tube voltages (120 and 140 kVp), slice thicknesses (0.4-10 mm), and reconstruction filters. Statistical analyses included repeated-measures ANOVA with post-hoc pairwise comparisons.
Results
In-plane spatial linearity measured 50.00±0.06 mm (nominal 50 mm). CT number accuracy met manufacturer specifications except for bone in specific protocols. Mean CTDIvol discrepancy was 3.8±4.6%, with excellent dose-length product agreement (0.9±2.3%). RED measurements showed statistically significant but clinically insignificant protocol variations (mean HU shifts: -23.0 to 7.9 HU). Position-dependent effects showed mean HU reductions up to 23.2 HU at peripheral locations. Iterative metal artifact reduction (iMAR) differentiated Titanium and Stainless Steel implants without significantly affecting surrounding tissue HU values (P>0.08).
Conclusion
The Siemens NAEOTOM Alpha SPCCT scanner satisfies task group requirements for radiotherapy simulation. Its enhanced spatial resolution, spectral imaging capabilities, and flexible retrospective reconstruction offer significant advantages for radiation oncology, including improved target delineation and treatment planning accuracy.