Room: ePoster Forums
Purpose: To determine the impact of including density information into the generalized equivalent uniform dose (gEUD) formulation, defined as mass-weighted gEUD (mgEUD). gEUD and mgEUD were used to model normal tissue complication probability (NTCP) for pneumonitis in non-small cell lung cancer (NSCLC) patients.
Methods: mgEUD was defined similarly to gEUD, but instead of voxel volume, voxel mass was used in the formula. Twenty-one patients treated for NSCLC were retrospectively studied. All patients were graded for radiation pneumonitis based on the common terminology criteria for adverse events. Seventeen patients experienced pneumonitis with differing grades:(4) grade-1, (9) grade-2 and (4) grade-3. The PTV contours were subtracted from both lungs and the values for gEUD and mgEUD were calculated for the resulting structure. Paired two-tailed t-test was performed to determine statistical significant differences between mgEUD and gEUD ( p â‰¤ 0.05). Also, the best fit of a-parameter used between 1.0, 1.1 and 1.2 was determined. Curve fitting according to the Lyman-Kutcher-Burman (LKB) model was performed using MATLAB curve fitting toolbox.
Results: The best fitting a-parameter for gEUD and mgEUD was determined to be 1.2, with corresponding coefficient of determination of 0.87 and 0.86 for gEUD and mgEUD, respectively. The percent differences between gEUD and mgEUD were on average 5.8% (SD = 7.5%) with no significant difference. Evaluating pneumonitis grade â‰¥ 2 showed that mgEUD values had smaller standard deviation than gEUD. The standard deviations of mgEUD for grade-2 and grade-3 were 2.51 and 4.81, respectively, and were 2.9 for grade â‰¥ 2 and 5.14 for grade-3 for gEUD.
Conclusion: Differences between gEUD and mgEUD were not significant for NSCLC. The clustering of mgEUD values for gradeâ‰¥ 2, indicates it may be a better model for pneumonitis prediction. A larger cohort may show a more robust difference between gEUD and mgEUD for the lungs.
Not Applicable / None Entered.