ESTRO 36 Abstract Book

S490 ESTRO 36 2017 _______________________________________________________________________________________________

quantitative

image-based

structural

tissue

characterization was performed. Material and Methods

T2-weighted and T1-weighted MRI after contrast agent (CA) injection at 1.5T were acquired in thirteen patients before RT (MRI1) and at about 12 months of follow-up (MRI2). In order to reduce possible errors due to non- quantitative values of signal intensity, a normalization step was performed between MRI1 and MRI2 of each patient, using a histogram matching method. Right and left internal obturator muscle contours were manually delineated upon T2w MRI1 by an expert and then automatically propagated on MRI2 by an elastic registration method. The following textural features were extracted in each volume: histogram-based indices (mean intensity, variance, 95 th percentile, entropy, skewness, kurtosis), GLCM (Grey-Level Co-occurrence Matrix)-based indices (energy, correlation, homogeneity, entropy, contrast, dissimilarity), NGTDM (Neighborhood Grey-Tone Different Matrix)-based indices (coarseness, contrast, busyness, complexity, strength) and fractal dimension. To assess changes in internal obturator muscles, a comparison of the parameters extract on MRI1 and MRI2 was carried out by Wilcoxon test, with significant p-value Exemplificative T1w MRI1 and MRI2 with relative muscles histograms were shown in Figure 1. From a qualitative assessment, a homogenous higher enhanced area (red circle in Figure 1) was localized in MRI2 in a region near the prostate. Quantitatively, significant increase in mean, variance and 95 th percentile values on both T1w MRI and T2w MRI2 was also found, as well as variation of indices describing histogram shape as visible by the histograms reported in Figure 1. Moreover, changes of GLCM and NGTDM-based indices confirmed that the spatial distribution of this intensity enhancement was concentrated in a homogeneous local area, as suggested by increased homogeneity and correlation indices and decreased complexity and fractal dimension (Table 1). < 0.05. Results

Conclusion In patients who underwent RT for prosta te cancer treatment, an increase in signal intensity of t he internal obturator muscles was observed. Specifi cally, this enhancement was concentrated in the area near the prostate, likely to be included in high dose regions. This evidence was present both in T2w and T1w post CA injection MRI and can be compatible with an inflammatory status that normally follows RT. This inhomogeneous structural variation may be explained by the spatial dose distribution. Moreover, correlations with toxicity scores should be investigated, considering the involvement of the pelvic floor muscles in the urinary dysfunctions. PO-0897 Atlas-based auto-segmentation of heart structures in breast cancer patients R. Kaderka 1 , R. Mundt 1 , A. Bryant 1 , E. Gillespie 1 , B. Eastman 1 , T. Atwood 1 , J. Murphy 1 1 University of California San Diego, Department of 858- 822-4842, San Diego, USA Purpose or Objective Radiation therapy deposited in the heart increases the risk of ischemic heart disease, and sudden cardiac death. Reproducible contouring of the heart on CT imaging represents a critical component of treatment planning, though the literature demonstrates substantial variability in contouring among providers. In this study we assess the accuracy of an atlas-based auto-segmentation approach of the whole heart and the left anterior descending artery (LAD). Material and Methods We randomly selected a cohort of 38 breast cancer radiotherapy patients treated between 2014 a nd 2016. For all patients the whole heart and LAD were manually contoured according to guidelines published by Feng et al. (2011). The patients were divided into a training dataset (N=18), and a test dataset (N=20). We used the training dataset to create a contouring atlas using commercially