Purpose: In radiation therapy (RT) planning for thoracic cancers, it is desirable to minimize irradiation of functional lung volume (FLV) which may be mapped by the distribution of ventilation and perfused blood volume (PBV). This work investigates the feasibility of delineating FLV using dual-energy CT (DECT) and 4DCT.
Methods: DECT data with iodine-based intravenous contrast and 4DCT acquired during standard RT simulation using a dual-source DECT scanner (Drive, Siemens-Healthineers, Germany) for 10 lung cancer patients were analyzed. DECT was acquired simultaneously at two tube voltages, 80 and Sn140 kV, carefully synchronizing with contrast dynamics. For each patient the PBV was calculated via post-processing at the console. The lung ventilation per lobe was calculated from the 4DCT using a prototype software, based on the maximum inspiration and expiration phases. FLV was delineated as the regions with perfusion in the 95ᵗʰ percentile of the 2 highest ventilated lung lobes. To demonstrate the use of FLV, IMRT/SBRT plans generated with and without avoiding FLV were compared.
Results: The regions of high perfusion and ventilation were generally not correlated. The average PBV in arbitrary units was 43.2±17.3, and the average ventilation was 14.7±8.4% which varied across the 5 lung lobes from 13.4±6.5% for the right middle lobe to 16.2±6.0% for the right upper lobe. The FLVs were in the range of 0.4-2.5% of the whole lung volume. For a representative IMRT/SBRT lung cancer with a prescription of 50 Gy, the plan considering FLV as an avoidance organ had the mean dose to the FLV of 4.7 Gy, compared to 7.5 Gy for the plan without avoiding the FLV.
Conclusion: Lung PBV and ventilation maps derived from contrast-enhanced DECT 4DCT acquired during standard RT simulation may provide a new tool to delineate functional lung volume, useful for RT planning in the thorax.
Funding Support, Disclosures, and Conflict of Interest: Partially supported by Siemens Healthineers