Room: ePoster Forums
Purpose: To estimate the clinical impact of the differences between delivered and planned dose using normal tissue complication probability (NTCP) modeling. Further, to evaluate the dependence of the results on imaging modality and deformable image registration (DIR) algorithm.
Methods: 57 prostate cancer patients were included in the study. 47 were treated with IMRT using CT-on-rails (CTOR) for daily IGRT and 10 with VMAT using cone beam CT (CBCT), respectively. The delivered dose distributions to bladder and rectum were calculated using two DIR algorithms (intensity-based and contour-based) and were compared with the respective planned doses. For the calculation of the normal tissue complication probabilities (NTCP), the Relative Seriality model was used with the following parameter values: D50 = 81.0 Gy, Î³ = 0.44, s = 0.0001 for bladder and D50 = 67.0 Gy, Î³ = 2.5, s = 1.0 for rectum.
Results: For CTOR, the NTCP of the treatment plan was 22.3 (Â±8.4) for bladder and 12.6 (Â±5.9) for rectum. The respective values for the contour-based DIR algorithm were 23.2 (Â±8.4) for bladder and 9.9 (Â±8.3) for rectum. The values for the intensity-based DIR algorithm were 25.1 (Â±8.0) for bladder and 11.0 (Â±10.4) for rectum, respectively. Similarly, for CBCT, the NTCP of the treatment plan was 16.9 (Â±6.4) for bladder and 5.5 (Â±9.4) for rectum. The respective values for the contour-based DIR algorithm were 17.3 (Â±6.9) for bladder and 5.9 (Â±12.9) for rectum. The values for the intensity-based DIR algorithm were 19.4 (Â±7.8) for bladder and 4.7 (Â±10.6) for rectum, respectively.
Conclusion: The average NTCP values of the estimated delivered doses to bladder and rectum were similar and lower, respectively compared to the values calculated from the respective plans for the contour-based DIR for both imaging modalities. For the intensity-based DIR algorithm, the same pattern is observed for the CTOR.