Delineation of Spatially-Varied High-Risk GTV in Pancreatic Adenocarcinoma Using MRI-ADC Maps

Abstract

Purpose/Objective(s)Poor differentiation correlates with invasiveness and metastasis of pancreatic adenocarcinoma (PAC). Recently, apparent diffusion coefficient (ADC) values derived from diffusion-weighted (DW) MRI were shown to correlate with histopathological grade in gliomas. The purpose of this study was to investigate whether: 1) ADC values correlate with histopathological grade in PAC, 2) high-risk regions within PAC can be identified by thresholding ADC parameter maps, and 3) ADC parameter maps can be used to evaluate chemo-radiation treatment response.Materials/MethodsDW-MRI data were acquired using a 3T MRI scanner for a total of 16 patients with resectable, borderline resectable, and unresectable PAC. Of these, 5 patients had DW-MRI prior to and following completion of chemo-radiation treatment. Gross tumor volumes (GTV) for each patient were manually delineated on the corresponding ADC maps. The mean ADC value for each GTV was computed and compared against reported histopathologic grade of well/moderately (G1/G2) and poorly (G3) differentiated, high-risk. PAC and poorly differentiated GTVs were then constructed by thresholding ADC maps using the mean ADC values from PAC and G3 groups, respectively. The thresholded ADC derived GTV was then compared against manually delineated GTV volumes using a Mann-Whitney test. Finally, pre- and post-treatment mean ADC values were compared using a Wilcoxon matched pairs test.ResultsMean and standard deviation ADC values of histopathologically-proven PAC, well/moderately differentiated, and poorly differentiated was 1.66 ± 0.2 × 10-3, 1.74 ± 0.14 × 10-3, and 1.46 × 10-3 mm2/sec, respectively. Thresholded ADC GTV volumes were not significantly different from manually defined GTV volumes (p = 0.4). G3 defined GTVs were smaller than PAC defined GTVs contours and were confined within PAC GTV. Increased post-treatment ADC values (1.33 ± 0.12 vs 1.68 ± 0.17) and significant decreased ADC volumes (15.76 ± 10.1 cm3 vs 23.19 ± 11.9 cm3) (p = 0.0417) were observed in all five patients studied. However, no significant differences in pre-/post-treatment ADC values were detected in this small sample of patients (p = 0.116).ConclusionsADC values correlate with histopathological grade in PAC. PAC GTV’s constructed by thresholding ADC parameter maps result in similar volumes as manually defined GTVs, with the additional advantage of reducing subjectivity. Although additional studies are needed, the high-risk GTVs obtained in this study suggest that the spatial variance in ADC values may be used to guide dose painting for radiation therapy of PAC. Purpose/Objective(s)Poor differentiation correlates with invasiveness and metastasis of pancreatic adenocarcinoma (PAC). Recently, apparent diffusion coefficient (ADC) values derived from diffusion-weighted (DW) MRI were shown to correlate with histopathological grade in gliomas. The purpose of this study was to investigate whether: 1) ADC values correlate with histopathological grade in PAC, 2) high-risk regions within PAC can be identified by thresholding ADC parameter maps, and 3) ADC parameter maps can be used to evaluate chemo-radiation treatment response. Poor differentiation correlates with invasiveness and metastasis of pancreatic adenocarcinoma (PAC). Recently, apparent diffusion coefficient (ADC) values derived from diffusion-weighted (DW) MRI were shown to correlate with histopathological grade in gliomas. The purpose of this study was to investigate whether: 1) ADC values correlate with histopathological grade in PAC, 2) high-risk regions within PAC can be identified by thresholding ADC parameter maps, and 3) ADC parameter maps can be used to evaluate chemo-radiation treatment response. Materials/MethodsDW-MRI data were acquired using a 3T MRI scanner for a total of 16 patients with resectable, borderline resectable, and unresectable PAC. Of these, 5 patients had DW-MRI prior to and following completion of chemo-radiation treatment. Gross tumor volumes (GTV) for each patient were manually delineated on the corresponding ADC maps. The mean ADC value for each GTV was computed and compared against reported histopathologic grade of well/moderately (G1/G2) and poorly (G3) differentiated, high-risk. PAC and poorly differentiated GTVs were then constructed by thresholding ADC maps using the mean ADC values from PAC and G3 groups, respectively. The thresholded ADC derived GTV was then compared against manually delineated GTV volumes using a Mann-Whitney test. Finally, pre- and post-treatment mean ADC values were compared using a Wilcoxon matched pairs test. DW-MRI data were acquired using a 3T MRI scanner for a total of 16 patients with resectable, borderline resectable, and unresectable PAC. Of these, 5 patients had DW-MRI prior to and following completion of chemo-radiation treatment. Gross tumor volumes (GTV) for each patient were manually delineated on the corresponding ADC maps. The mean ADC value for each GTV was computed and compared against reported histopathologic grade of well/moderately (G1/G2) and poorly (G3) differentiated, high-risk. PAC and poorly differentiated GTVs were then constructed by thresholding ADC maps using the mean ADC values from PAC and G3 groups, respectively. The thresholded ADC derived GTV was then compared against manually delineated GTV volumes using a Mann-Whitney test. Finally, pre- and post-treatment mean ADC values were compared using a Wilcoxon matched pairs test. ResultsMean and standard deviation ADC values of histopathologically-proven PAC, well/moderately differentiated, and poorly differentiated was 1.66 ± 0.2 × 10-3, 1.74 ± 0.14 × 10-3, and 1.46 × 10-3 mm2/sec, respectively. Thresholded ADC GTV volumes were not significantly different from manually defined GTV volumes (p = 0.4). G3 defined GTVs were smaller than PAC defined GTVs contours and were confined within PAC GTV. Increased post-treatment ADC values (1.33 ± 0.12 vs 1.68 ± 0.17) and significant decreased ADC volumes (15.76 ± 10.1 cm3 vs 23.19 ± 11.9 cm3) (p = 0.0417) were observed in all five patients studied. However, no significant differences in pre-/post-treatment ADC values were detected in this small sample of patients (p = 0.116). Mean and standard deviation ADC values of histopathologically-proven PAC, well/moderately differentiated, and poorly differentiated was 1.66 ± 0.2 × 10-3, 1.74 ± 0.14 × 10-3, and 1.46 × 10-3 mm2/sec, respectively. Thresholded ADC GTV volumes were not significantly different from manually defined GTV volumes (p = 0.4). G3 defined GTVs were smaller than PAC defined GTVs contours and were confined within PAC GTV. Increased post-treatment ADC values (1.33 ± 0.12 vs 1.68 ± 0.17) and significant decreased ADC volumes (15.76 ± 10.1 cm3 vs 23.19 ± 11.9 cm3) (p = 0.0417) were observed in all five patients studied. However, no significant differences in pre-/post-treatment ADC values were detected in this small sample of patients (p = 0.116). ConclusionsADC values correlate with histopathological grade in PAC. PAC GTV’s constructed by thresholding ADC parameter maps result in similar volumes as manually defined GTVs, with the additional advantage of reducing subjectivity. Although additional studies are needed, the high-risk GTVs obtained in this study suggest that the spatial variance in ADC values may be used to guide dose painting for radiation therapy of PAC. ADC values correlate with histopathological grade in PAC. PAC GTV’s constructed by thresholding ADC parameter maps result in similar volumes as manually defined GTVs, with the additional advantage of reducing subjectivity. Although additional studies are needed, the high-risk GTVs obtained in this study suggest that the spatial variance in ADC values may be used to guide dose painting for radiation therapy of PAC.