Phase 1-2 Study of Dual-Energy Computed Tomography for Assessment of Pulmonary Function in Radiation Therapy Planning

To quantify lung function according to a dual-energy computed tomography (DECT)-derived iodine map in patients treated with radiation therapy for lung cancer, and to assess the dosimetric impact of its integration in radiation therapy planning.

Patients treated with stereotactic ablative radiation therapy for early-stage or intensity modulated radiation therapy for locally advanced lung cancer were prospectively enrolled in this study. A DECT in treatment position was obtained at time of treatment planning. The relative contribution of each voxel to the total lung function was based on iodine distribution. The composition of each voxel was determined on the basis of a 2-material decomposition. The DECT-derived lobar function was compared with single photon emission computed tomography/computed tomography (SPECT/CT). A functional map was integrated in the treatment planning system using 6 subvolumes of increasing iodine distribution levels. Percent lung volume receiving 5 Gy (V5), V20, and mean dose (MLD) to whole lungs (anatomic) versus functional lungs were compared.

Twenty-five patients with lung cancer, including 18 patients treated with stereotactic ablative radiation therapy and 7 patients with intensity modulated radiation therapy (locally advanced), were included. Eighty-four percent had chronic obstructive pulmonary disease. Median (range) forced expiratory volume in 1 second was 62% of predicted (29%-113%), and median diffusing capacity of the lung for carbon monoxide was 56% (39%-91%). There was a strong linear correlation between DECT- and SPECT/CT-derived lobar function (Pearson coefficient correlation r=0.89, P<.00001). Mean (range) differences in V5, V20, and MLD between anatomic and functional lung volumes were 16% (0%-48%, P=.03), 5% (1%-15%, P=.12), and 15% (1%-43%, P=.047), respectively.

Lobar function derived from a DECT iodine map correlates well with SPECT/CT, and its integration in lung treatment planning is associated with significant differences in V5 and MLD to functional lungs. Future work will involve integration of the weighted functional volume in the treatment planning system, along with integration of an iodine map for functional lung-sparing IMRT.