Early Assessment of Treatment Responses during Radiation Therapy of Lung Cancer Based on Quantitative Analysis of Daily CT

Publication date: Available online 21 February 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Jijo Paul, Cungeng Yang, Hui Wu, An Tai, Entesar Dalah, Cheng Zheng, Candice Johnstone, Feng-Ming Kong, Elizabeth Gore, X. Allen Li
PurposeTo investigate early tumor and normal tissue responses during the course of radiation therapy (RT) of lung cancer based on quantitative analysis of daily CTs.Methods and materialsDaily diagnostic-quality CTs acquired using CT-on-Rails during CT-guided RT for 20 lung cancer patients were quantitatively analyzed. On each daily CT set, contours of gross tumor volume (GTV) and lungs were generated and the x-ray dose delivered was reconstructed. The changes in CT image intensity (Hounsfield unit, HU) features in the GTV and in the multiple normal lung tissue shells around GTV were extracted from daily CTs. Associations between the changes in mean HU, GTV volume, accumulated dose during RT delivery and patient survival rate were analyzed.ResultsDuring the course of RT, radiation can induce substantial changes in HU histogram features in the daily CTs with reductions of GTV mean HU (dH) observed in the range of 11- 48HU (median 30HU). The dH is statistically related to the accumulated GTV dose (R² >0.99), while it is weakly correlated with the change of GTV (R²= 0.3481). Statistically significant increases in patient survival rates (p= 0.038) were observed for patients with higher dH in GTV. In normal lung, the four regions proximal to the GTV showed statistically significant (<0.001) HU reductions from the first to last fractions.ConclusionQuantitative analysis of daily CT indicates that the mean HUs in lung tumor and the surrounding normal tissue were reduced during RT delivery. This reduction was observed in the early phase of the treatment and is patient specific and correlated to the delivered dose. Larger HU reduction in GTV is significantly correlated with higher patient survival. The change of daily CT feature, such as mean HU, may be used for early assessment of radiation responses during RT delivery for lung cancer.

Teaser

Changes in CT intensity, including Hounsfield Unit (HU) histogram and mean HU, on daily diagnostic-quality CTs acquired during CT-guided radiation therapy delivery for lung cancers were studied. The observed mean HU reductions in the tumor and in the surrounding lung tissues were patient specific and significantly correlated with the radiation doses delivered and with patient survival rate. Such HU reduction may potentially be used as early assessment of radiation response.


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