Room: Exhibit Hall | Forum 5
Purpose: Dose delivered to patients may be different from planned dose due to possible anatomical change and motion variation between simulation and treatments. On-board 4D-CBCT offers patientsâ€™ updated anatomical information and motion patterns on treatment day, which can be used to reconstruct actual dose delivered on during treatment. Leveraging an advanced 4D-CBCT technique based on simultaneous motion estimation and reconstruction (SMEIR), we developed a 4D dose reconstruction tool to evaluate actual delivered dose with comparison to planned dose.
Methods: For each evaluated patient, 10 phases 4D-CBCT were reconstructed by SMEIR from half-fan CBCT projections. Planning 4D-CT was registered to 4D-CBCT phase to phase to generate a group of 4D-mCBCT images keeping geometric information of 4D-CBCT while containing HU of 4D-CT. Using the delivered SBRT plan, doses were calculated in the Eclipse treatment planning system on each phase of 4D-mCBCT. 4D-mCBCT doses were deformed to the reference end-of-exhale phase using deformation vector fields (DVFs) from SMEIR to get accumulated 4D-mCBCT dose as delivered dose. Using the same delivered plan, accumulated 4D planned doses were obtained through deforming doses of other phases to the reference phase using inter-phase DVFs generated by BSpline deformable image registration from planning 4D-CT. Dose-volume histogram (DVH) of GTV and OARs were quantitatively compared between planned and delivered dose. Seven lung cancer patients treated by SBRT with eight targets were used for this dose reconstruction and evaluation study.
Results: For all targets, more than 99% volume of GTV is covered by prescription dose based on accumulated dose calculated from 4D-mCBCT. Accumulated doses of OARs based on 4D-mCBCT matched well to that in accumulated planned dose based on planning 4D-CT.
Conclusion: We developed a dose reconstruction tool based on SMEIR reconstructed 4D-CBCT images for lung SBRT. Excellent agreement was observed between planned and delivered doses on GTV and OARs.