ESTRO 2022 - Abstract Book

S1549

Abstract book

ESTRO 2022

Poster (digital): Physical aspects of quantitative functional and biological imaging

PO-1748 A DECT framework to measure the effect of radiation dose on lung function after radiotherapy

M. Simard 1,2 , A. Lapointe 3 , H. Bahig 3 , J. Carrier 1,2,3 , S. Zhang 3 , M. Campeau 3 , É. Filion 3 , D. Roberge 3 , H. Bouchard 1,2,3 , S. Bedwani 3,2 1 Université de Montréal, Physique, Montréal, Canada; 2 Centre hospitalier de l’Université de Montréal, Centre de recherche, Montréal, Canada; 3 Centre hospitalier de l’Université de Montréal, Radio-oncologie, Montréal, Canada Purpose or Objective To propose a contrast-enhanced dual-energy CT (DECT) framework to study dose effect on lung function after radiotherapy and validate the usefulness of the framework with a case study of four patients. Materials and Methods Four lung cancer patients received a DECT scan (Siemens SOMATOM Definition Flash) with intravenous iodine injection before the radiotherapy treatment ( τ =0), and at τ =6 and τ =12 months post-treatment. Post-treatment DECT scans were registered on the pre-treatment scans using the Advanced Normalization Tools (ANTs) software to allow correspondence with the dose map. Iodine maps were estimated with a two-material decomposition using lung and iodine as basis materials, and a stoichiometric calibration procedure. As iodine concentration may vary importantly between patients and times τ , it is not a purely quantitative metric. A different metric, the normalized function (NF), is reported. The NF is defined as the ratio of mean iodine concentration in a given region of interest normalized by the mean iodine concentration in a reference region. The reference region is defined as a well perfused volume that received low dose (under 5 Gy). Furthermore, the functional response (FR) is defined as the relative variation of the NF between pre-treatment and post-treatment scans. Results Figure 1 shows examples of fully registered CT images along with the corresponding functional data (NF images) for each of the four patients and τ =0, 6 and 12 months. The apparition of fibrosis (patients 1 and 3) or the general loss of function after treatment (patients 3 and 4) is recognizable. Figure 2 shows the metrics NF and FR for selected regions of interest. On the top row, the NF is shown for each of the five lung lobes (right and left inferior RI and LI, right middle RM, right and left superior RS and LS). Tumor location for all patients correlate with poor NF at τ =12 months compared to other lobes, suggesting that the loss of function is important close to the tumor. The bottom row of figure 2 shows the FR for three dose ranges (<5 Gy, 5-20 Gy, >20 Gy) for each patient. It is shown that lung regions which received higher dose are generally associated with a more important loss of function over time. The metric thus allows comparing the relative response to radiation between patients.