Quantifying Similarity Of Strut-Adjusted Volume Implant (SAVI) Applicator In Accelerated Partial Breast Irradiation (APBI) HDR Bachytherapy
K Li1 2* J Newton 1 2 (1) John R. Marsh Cancer Center, HAGERSTOWN, MD, (2) Associates In Medical Physics, Lanham, MDPO-BPC-Exhibit Hall-2 Saturday Room: Exhibit Hall
Purpose: In order to provide guidelines to determine the appropriateness for HDR Brachytherapy with strut-adjusted volume implant (SAVI) applicator, the different magnitudes of distortion, rotation and displacement were quantitatively analyzed by a distance comparison method based on markers built in SAVI applicator.
Methods:A SAVI 8-1 applicator was used for this study. After a CT scan of the applicator, a set of Digitally Reconstructed Radiographs (DRR) for orthogonal fields were generated as a reference and used to check the consistency of the applicator during treatment course. Then, the SAVI applicator was set up on the table using three different scenarios which are parallel rotation, central axis rotation, and diameter variation of applicator. These three scenarios included all the possibilities of the patient alignment and displacement. The sum of the marker to marker distance was used to evaluate the similarity level of the SAVI applicator due to different setup variations.
Results:In this study, given the full expansion of SAVI applicator, for parallel rotation, using anterior posterior (AP) imaging, the average distance sum for three markers was 9.56cm, and STDV was 0.02cm. For axial rotation, using AP imaging, the average distance sum was 9.7cm, and STDV was 0.3cm; and using Lateral imaging, the average distance sum was 7.4cm and STDV was 1.5cm. For AP imaging with a 45 degree alignment of the applicator, as the diameter went from 3.5cm to 1.5cm, the distance sum was not highly sensitive; however, laterally the distance sum changed from 9.1cm to 6.4cm.
Conclusion:Clinically, it is better to check both of the marker distance sum and furthest strut distance as well as skin mark to determine the appropriateness for APBI HDR treatment. Further outcome studies should develop a safe treatment margin based on translation and rotational matrix as with given marker coordinates.