2460 - Integrating SECT and DECT in Radiotherapy: keV Optimization for Simplified Workflows and Accurate Dose Calculation

Purpose/Objective(s):

Dual-energy CT (DECT) enhances soft tissue contrast and allows for advanced reconstructions like virtual monoenergetic (VMI) and virtual noncontrast (VNC) images. However, its clinical use is limited by the need for separate Hounsfield look-up tables (HLUTs) and concerns about dose calculation accuracy. This study aims to: (1) identify optimal VMI energies that closely match conventional 120kVp scans across different anatomical sites; (2) confirm dosimetric accuracy using site-specific optimal keV and VNC images; and (3) evaluate if a unified HLUT can simplify SECT-DECT workflows.

Materials/Methods:

Ten patients (head, neck, chest, abdomen/pelvis) scanned on GE Revolution CT were analyzed. Conventional 120kVp and GSI spectral scans were acquired. Using a CIRS phantom, RMSE of CT numbers for tissue-equivalent inserts identified optimal VMI energies matching 120kVp for each site. HLUTs were established for: conventional noncontrast scans, site-optimized keV, 120kVp-like (74keV), and VNC images. VMAT plans were generated on conventional noncontrast scans (prostate:70Gy/25f; lung:66Gy/30f; H&N:69.96Gy/33f; bone metastasis:10Gy/1f). All plan parameters were applied identically to DECT images for dose recalculation. PTV and OAR dose differences were evaluated using DVH parameters; gamma analysis (2%/2mm) assessed dose agreement. Comparisons: 120kVp SECT vs. optimal keV DECT vs. 120kVp-like DECT, and conventional noncontrast vs. contrast-enhanced SECT vs. DECT VNC.

Results:

SECT HLUTs showed minimal intersite variation with nearly overlapping curves. Site-optimized keV: abdomen 68keV (RMSE 8.2±3.1HU), head 72keV (7.5±2.8HU), chest 70keV (9.1±3.5HU), neck 72keV (8.7±3.3HU). These differed slightly from 120kVp-like (74keV), primarily in high-density bone. Dose calculations with optimized keV matched 120kVp SECT: PTV mean dose difference 0.3±0.2%; OAR mean doses <1%; gamma >99% in all except one metal implant case receiving SBRT for bone metastasis, where larger target deviations were observed. Overall dose differences: 120kVp SECT ˜ optimal keV DECT ˜ 120kVp-like DECT (median ±0.39%). VNC images showed dose differences <0.2% vs. conventional noncontrast scans.

Conclusion:

Site-specific optimal keV images from DECT (68keV for abdomen, 72keV for head and neck, 70keV for chest) offer dose calculation accuracy similar to traditional 120kVp scans. Despite slight differences from the 120kVp-like value (74keV), the dosimetric impact is minimal, allowing for a unified HLUT in SECT and DECT workflows. VNC images match the dosimetric performance of conventional noncontrast scans for abdomen and head in standard fractionation. This method streamlines clinical workflows, reduces HLUT maintenance, and minimizes error risk—enabling a smooth transition to DECT-based planning. Further research is needed for cases involving metal implants.