Quantitative assessment of dose accumulation uncertainty using a commercial deformable image registration algorithm
Yihang Xu1, John Chetley Ford1, Kyle R Padgett2
1Department of Radiation Oncology, University of Miami Miller School of Medicine, Miami, FL, USA.
Introduction:
This work aims to quantify the dose accumulation uncertainty for prostate adaptive intensity modulated proton therapy (IMPT).
Methods:
Pelvic CT images from ten prostate patients with 6 repeat CT (rCT) scans were selected. The reference DVFs (DVFref) were generated by performing DIR between planning CT (pCT) and rCTs using a reference DIR algorithm. Pseudo-rCTs were created by deforming pCT to rCTs using the DVFref. An IMPT plan was created for each patient on pCT, which was recalculated on each pseudo-rCT. The fractional dose was warped back to pCT using DVF (DVFtest) generated by a commercial DIR algorithm which uses a 'deformable multi pass (DMP)' algorithm or 'structure-guided deformable (SGD)' if DMP failed. The DVFtest deformed dose was compared to the DVFref deformed dose. Registration error (RE) and inverse consistency error (ICE) were assessed for DVFtest.
Results:
When using only DMP, the RE throughout the whole body was 1.17 ± 1.22 mm. Overall, the ICE for all voxels was 0.18 ± 0.5 mm. The dose deformation uncertainty was 0.02 % ± 2.53 % over the whole body, with the highest uncertainty observed in the bladder (0.83 % ± 6.66 %) and high dose gradient regions. When incorporating SGD, the dose deformation uncertainty inside the CTV was changed from 0.11 % ± 2.42 % to 0.15 % ± 1.4 %, and the uncertainty range of dose accumulation for CTV V100 was reduced from (-3.39 %, 5.49 %) to (-0.31 %, 3.43 %).
Conclusions:
This study demonstrated that a commercial DIR algorithm is well-suited for prostate IMPT dose accumulation with acceptable geometric and dosimetric uncertainty. The incorporation of SGD has the potential to reduce the uncertainty.
