Raman spectroscopy for assessment of radiation therapy response: Pre-clinical animal study results for lung cancer

Abstract

The purpose of this study is to explore whether Raman spectroscopy is able to assess the response of lung tumors and healthy lung tissue in mice following radiation therapy. 4T1 mouse breast cancer cells injected intramuscularly metastasize to the lungs at day 14. These 4T1 cancer cells were injected subcutaneously into the flanks of 18 Balb/C female mice. Five additional mice were used as “normal lung” controls. After 14 days, cohorts of mice bearing tumors received 6, 12 or 18 Gy to the left lung with 6MV photons. Five mice were treated as “unirradiated tumor” controls. After 24- 48 hours, lungs were excised and the specimens were sectioned for Raman measurements and pathologic evaluation using a cryostat-microtome. A total of 775 Raman spectra were collected; 107 from unirradiated normal lung tissues, 126 from unirradiated tumors, and 318 from tumors irradiated with 6, 12 or 18 Gy. Raman spectra were also collected from normal lung tissues of mice with unirradiated tumors (29) as well as irradiated (6, 12 or 18 Gy) tumors (195). Principal component analysis (PCA) and discriminant function analysis (DFA) were performed to analyze and interpret the results. Normal lung tissues and tumors were identified 100% of the time relative to pathologic scoring. Raman spectral data showed prominent results between unirradiated tumor and tumors receiving 12 or 18 Gy. Thus, in a model consisting of unirradiated and irradiated tumors (12 or 18 Gy) classification accuracies were 97.6%, 79.6%, and 80.8%, respectively, relative to pathologic assessment. Overall, 85.4% distinguishability was observed for unirradiated and irradiated (6, 12 or 18 Gy) normal lung tissues. Preliminary results demonstrate the promise for Raman spectroscopy in the prediction of normal vs. lung tumors as well as in the assessment of response of tumor and normal lung tissues following radiation therapy.