1216 - CT Based Quantification of Radiation Induced Lung Damage (RILD) and the Interaction with Chemotherapy and Cetuximab

Abstract

ABSTRACT Purpose Radiation-induced lung damage (RILD) is one of the most important dose-limiting toxicities in the treatment of lung cancer patients. Prediction models are still unsatisfactory, partly because dyspnea as an endpoint is influenced by many other parameters than RILD and is difficult to quantify. Interactions between drugs and radiotherapy (RT) are thus difficult to assess. We therefore evaluated RILD more objectively, quantitatively and on a continuous scale measuring the changes of lung density per voxel before and after chemo-RT and with or without cetuximab. Methods CT scans from 55 stage III NSCLC patients were evaluated. Deformable registration was used to register the 3 month follow-up scans to the baseline scans. Changes in CT density in the lungs were correlated to the RT dose delivered in every part (i.e. voxel) of the lungs. Four different treatments were included: sequential chemo-RT (N = 9), concurrent chemo-RT (N = 17), concurrent chemo–RT with cetuximab (N = 19) from phase I trial (NCT00522886) and patients from the randomized phase II PET-boost trial (NCT01024829) receiving a higher radiation dose per fraction than the other groups (2.75 Gy) (N = 10). Patients with an increase of over 0.5 Hounsfield Units (HU) per Gy dose in each voxel of the lungs were considered as ‘responders’, i.e. showing susceptibility for RILD. Results Patients received a mean dose of 64.14 Gy(range 55-86 Gy) to the tumor, with a standard deviation of 11.3. The number of responders in patients treated in cetuximab was 16/19 (85%), in the concurrent chemo-RT group 11/16 (69 %), 7/10 (70 %) in the PET-boost patients and 4/9 (56 %) in the sequential chemo-RT group. The average increase in density was 2.6 HU per Gy for responders and 0.01 HU per Gy for non-responders. Conclusion CT density changes allow quantitative non-invasive assessment of RILD, giving complementary information to clinical endpoints. Large individual variability in the susceptibility for RILD could be shown by CT as well as treatment modality related differences. Disclosure All authors have declared no conflicts of interest.