Room: Exhibit Hall | Forum 5
Purpose: This study aims at examining the impact of imaging modality used for image guided radiotherapy (IGRT) and deformable image registration (DIR) algorithm in the accuracy of estimating the accumulated from all the fractions delivered dose distribution.
Methods: This analysis involves 20 prostate cancer patients treated with IMRT using CT-on-rails (CTOR) for daily IGRT and VMAT using Cone Beam CT (CBCT). A total of 453 fractions across those patients were analysed. MIM (MIM Software, Inc) was used to calculate the cumulative dose in bladder and rectum utilizing two different DIR algorithms (intensity-based and contour-based). Manually contours drawn on each CTOR or CBCT image were used as a reference for the contour-based DIR. Three dosimetric metrics were used for the comparisons (mean dose, D1cc and V50).
Results: In the case of CTOR, the deviation of the cumulative mean dose to bladder against the planned dose was 1.4Â±2.1Gy for bladder and -3.2Â±5.3Gy for rectum for the intensity-based DIR and 1.5Â±2.0Gy and -3.9Â±2.7Gy for the contoured-based DIR. The respective values for V50 were 3.0Â±3.2% for bladder and -6.1Â±18.3% for rectum for the intensity-based DIR and 3.2Â±3.8% and -8.9Â±8.3% for the contoured-based DIR. Similarly, in the case of CBCT, the deviation of the cumulative mean dose to bladder against the planned dose was 14.5Â±8.6Gy for bladder and -1.7Â±10.6Gy for rectum for the intensity-based DIR and -15.2Â±46.0Gy and -31.2Â±52.4Gy for the contoured-based DIR. The respective values for V50 were 14.8Â±8.4% for bladder and 56.0Â±101.8% for rectum for the intensity-based DIR and -25.7Â±50.1% and -39.0Â±55.4% for the contoured-based DIR.
Conclusion: The dosimetric analysis showed that the contour-based DIR algorithm performed much better than the intensity-based DIR in all the cases. The used of CTOR helped also both DIR algorithms perform better compared to CBCT.