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Investigation Into the Accuracy of Deformable Registration Algorithms for Use in Dose Summation: A Case Study in Combined Modalities


C Chuang

C Chuang*, O Morin, J Pouliot, University of California San Francisco, San Francisco, CA

SU-E-J-96 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
To better understand the accuracy and limitation of deformable registration algorithms for dose summation by studying the results produced through two different deformable registration techniques for a clinical case of combining a Cyberknife radiosurgery plan and an electron boost to the scar tissues.

Methods:
A patient was treated with a Cyberknife plan with supine CT and an electron boost plan with prone CT concurrently. The CT, RT structures and dose grids were exported from the Cyberknife MultiPlan system and the Pinnacle system and imported into two commercial DICOM viewing systems equipped with deformable registration algorithms. One of the systems uses intensity-based free-form deformable registration while the other uses B-spline free-form deformable registration. The electron boost plan was first registered to the CK plan using rigid registration, then secondly using deformable registration in each system. The region of interest used for registration was chosen to encompass the whole CT volumes due to the supine vs. prone positions.

Results:
The summation doses for the Cyberknife CTV and critical structures do not differ between rigid registration and deformable registration for both systems. The electron boost volume does show higher mean dose received for the deformable registration compared with rigid registration for both systems (12.90 Gy vs. 11.71 Gy and 12.39 Gy vs. 11.53 Gy). There are slight variations between the doses produced by the two systems for all the structures, with an averaged difference of approximately 0.02 % to 2.63%.

Conclusions:
These results show that for cases like this one, where the two treatment volumes do not overlap, there will not be significant differences between rigid and deformable registration, and that the only significant difference in summation dose between the different deformable registration algorithms is where the volume is deformed the most, in this case, the electron boost volume.

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