Phase I-II Study of Dual-Energy Computed Tomography (DECT) for Assessment of Pulmonary Function in Radiotherapy Planning

Publication date: Available online 7 June 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Houda Bahig, Marie-Pierre Campeau, Andréanne Lapointe, Stephane Bedwani, David Roberge, Jacques de Guise, Danis Blais, Toni Vu, Louise Lambert, Carl Chartrand-Lefebvre, Martin Lord, Edith Filion
PurposeTo quantify lung function based on a dual energy computed tomography (DECT)-derived iodine map in patients treated with radiotherapy for lung cancer, and to assess the dosimetric impact of its integration in radiotherapy planning.MethodsPatients treated with stereotactic ablative radiotherapy (SABR) for early stage or intensity-modulated radiotherapy (IMRT) 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 based on a two-material decomposition. DECT-derived lobar function was compared to Single Photon Emission Computed Tomography / Computed Tomography (SPECT/CT). A functional map was integrated in treatment planning system using 6 sub-volumes of increasing iodine distribution levels. Percent lung volume receiving 5Gy (V5), V20 and mean dose (MLD) to whole lungs (anatomical) vs. functional lungs were compared.Results25 patients, including 18 patients with lung cancer treated with SABR and 7 patients with IMRT (locally advanced), were included. Eighty-four percent had chronic obstructive pulmonary disease. Median 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's coefficient correlation r= 0.89, p<0.00001). Mean differences in V5, V20 and MLD between anatomical and functional lung volumes were 16% (0-48%, p=0.03), 5% (1-15%, p=0.12) and 15% (1-43%, p=0.047), respectively.ConclusionLobar function derived from 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 weighted functional volume in the treatment planning system, along with integration of iodine map for functional lung-sparing IMRT.

Teaser

This prospective study evaluated the role of DECT-iodine maps for the assessment of lung function in radiotherapy planning. Using a 2-material decomposition method, iodine concentration of whole lung volume was used as an indicator of regional perfusion. DECT-iodine map provided accurate lung function information. Significant differences in mean and low dose to whole vs. functional lung volumes were found with integration of DECT-iodine maps in early and advanced stage lung cancer radiotherapy planning.


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