Correlation of normal lung density changes with dose after stereotactic body radiotherapy (SBRT) for early stage lung cancer

Abstract

Background and Purpose: To investigate the correlation between normal lung CT density changes with dose accuracy and outcome after stereotactic body radiation therapy (SBRT) for patients with early stage non-small-cell lung cancer (NSCLC). Materials and Methods: Thirty-one patients (with a total of 33 lesions) with non-small cell lung cancer were selected out of 270 patients treated with SBRT at a single institution between 2003 and 2009. Out of these 31 patients, 10 patients had developed radiation pneumonitis (RP). Dose distributions originally planned using a 1-D pencil beam-based dose algorithm were retrospectively recomputed using different algorithms. Prescription dose was 48 Gy in 4 fractions in most patients. Planning CT images were rigidly registered to follow-up CT datasets at 3-9 months after treatment. Corresponding dose distributions were mapped from planning to follow-up CT images. Hounsfield Unit (HU) changes in lung density in individual, 5 Gy, dose bins from 5 to 45 Gy were assessed in the peri-tumoral region. Correlations between HU changes in various normal lung regions, dose indices (V20, MLD, generalized equivalent uniform dose (gEUD)), and RP grade were investigated. Results: Strong positive correlation was found between HU changes in the peri-tumoral region and RP grade (Spearman's r = 0.760; p < 0.001). Positive correlation was also observed between RP and HU changes in the region covered by V20 for all algorithms (Spearman's r ! 0.738; p < 0.001). Additionally, V20, MLD, and gEUD were significantly correlated with RP grade (p < 0.01). MLD in the peri-tumoral region computed with model-based algorithms was 5-7% lower than the PB-based methods. Conclusion: Changes of lung density in the peri-tumoral lung and in the region covered by V20 were strongly associated with RP grade. Relative to model-based methods, PB algorithms over-estimated mean peri-tumoral dose and showed displacement of the high-dose region, which correlated with HU changes on follow-up CT scans.

Correlation Between Lung Density Changes Under Different Dose Gradients and Radiation Pneumonitis—Based on an Analysis of Computed Tomography Scans During Esophageal Cancer Radiotherapy

“…As Feghali et al. studies ( 5 ), ΔHu in peritumoral region was positively correlated with RP grade. Phernambucq et al.…”

“…The density change in this threshold range is related to the occurrence of RP. As Feghali et al studies (5), DHu in peritumoral region was positively correlated with RP grade. Phernambucq et al (7) found that the threshold dose of lung dose density change was 30 Gy, and there was only slight density change at low dose level.…”

“…Regarding the influence of the radiation dose on DHU there was an increase in lung density for increasing radiation doses for most dose intervals (6). However, the magnitude or threshold of density increase is inconsistent among various literature reports (7,26,27). We believed that the significantly higher CT value of 40 Gy (HU 20-40 ) time point might be related to the increased sensitivity of lung tissue from the 4th week of RT.…”

“…Phernambucq et al (7) found that the threshold dose of lung dose density change was 30 Gy, and there was only slight density change at low dose level. Aoki et al (26) analyzed that the minimum dose related to the change of CT lung density was 16 to 36 Gy (median dose was 24 Gy), while Boersma et al (27) normalized the data to obtain the dose-effect relationship of density change, which had little change in the middle and low-dose range. For such results, studies (18) suggest that the increase of CT density in low-dose areas of the lung may be due to the "relative" blood flow systematically redistributing to the less exposed areas, thus moderately increasing the tissue density or due to anatomical changes and/or inaccurate image registration.…”

“…Radiation induced lung tissue reactions, such as inflammatory cell infiltration, exudation, fibrin deposition and fibrosis, can lead to changes in lung density (2). Some studies suggest that computed tomography (CT) density changes not only reflect the changes of radiation-induced lung tissue, but also can be used to quantify radiation-induced lung injury (3)(4)(5). At present, some studies have focused on the correlation between the changes of lung density after RT and the dose of lung irradiation (6)(7)(8)(9), however, it is still unclear whether there is a correlation between lung radiation dose and lung density changes (DHU) during RT and whether DHU during RT are related to the occurrence of RP.…”