Quantitative Computed Tomography for Radiation-Induced Changes in Normal Breast Tissue During Partial Breast Irradiation International Journal of Radiation Oncology, Biology, Physics EPOSTER ABSTRACT| VOLUME 96, ISSUE 2, SUPPLEMENT , S191-S192, OCTOBER 01, 2016
Date
10/01/2016Abstract
Purpose/Objective(s)
Radiation-induced cosmetic side effects, such as breast fibrosis, are observed after radiation therapy (RT) for breast cancer, particularly after accelerated partial breast irradiation (APBI). Quantitative CT texture analysis has the potential to predict radiation-related changes that may result in side effects. In this study we investigated the feasibility of using quantitative CT as an imaging biomarker for early assessment of radiation-induced changes in breast tissue during the delivery of APBI.
Materials/Methods
Daily diagnostic-quality CT data acquired using an in-room CT during daily CT-guided APBI for 15 breast cancer patients were analyzed. Patients were treated in the prone position with a dose of 38.5 Gy in 10 fractions. On each daily CT set, the contours of the breast, lumpectomy cavity (LC), and clips were manually delineated consistent with those from the planning CT. The contour of normal breast tissue was generated by subtracting the LC and clips from the breast volume. Normal breast tissue was divided into a series of 1 cm concentric shells created by expanding LC by 1 cm increments inside the normal breast contour, excluding the clips. The mean radiation dose in each shell was calculated from the original dosimetry plan. The first-order CT texture parameters (e.g., Hounsfield Unit [HU] histogram, mean HU, entropy) were obtained in each contour and shell from each daily CT set using an in-house tool based on MATLAB. The changes of these parameters between daily CTs were analyzed using the two-tailed paired t-test.
Results
Noticeable changes in CT texture parameters were observed in CTs from the first to the last fraction. On average, the mean HU in normal breast tissue was increased by 2.5 ± 1.2 HU, which was significant (P < 0.001). On the same daily CT set, the mean HU in an inner shell is higher than that for an outer shell. The change of mean HU in the first (most inner) shell from the first to the last fraction is as high as 11 HU, and is 5.2 ± 4.0 in average over all patients. For 2/3 of patients, this change is larger for an inner compared to that for an outer shell, and coincides with the mean doses in these shells. The fact that not all patients follow this trend may indicate patient-specific responses. The increase of mean HU in breast tissue was associated with the level of breast pain.
Conclusion
Increase of mean HU in normal breast tissue was observed from the first to the last fraction CT sets acquired during APBI delivery. This increase is dependent on radiation dose. These changes in quantitative CT may reflect physical and/or chemical changes in the healthy tissue of the breast and may be used as an early predictor of acute and/or late treatment effects.
Author List
X. Chen, C. Bergom, A.D. Currey, T.R. Kelly, C. Edwin, A. Montes, & A. LiAuthor
Adam Currey MD Vice Chair, Professor in the Radiation Oncology department at Medical College of WisconsinView Online
