SU-E-T-93: Creation of Standardized APBI SAVI Cavities Using CT Registration

Authors


Abstract

Purpose:

Develop a consistent and rapid method of generating the initial cavity structure for Accelerated Partial Breast Irradiation (APBI) using the SAVI applicator.

Methods:

Four SAVI (Cianna Medical) applicators (6-1 Mini, 6-1, 8-1, and 10-1) were scanned on a CT simulator. The applicators were scanned in air with the CT slices (0.625mm axial thickness) perpendicular to the long axis of the applicator. Following scanning the CT images were transferred to Eclipse (Varian Medical Systems) and contours of the cavity were drawn. The cavity proximal and distal locations were defined according to MD specification. The scans and contours were then re-imported into the CT virtual simulation workstation.At the time of patient planning the appropriate applicator scan is anonymized and imported into Eclipse. In Brachytherapy Planning two Marker points are placed, one at the distal band location (cavity start) and the second at a defined distance along the applicator (cavity end). The actual patient scan is then registered to the applicator scan. A three point match is used to quickly get the two scans in approximate alignment. Manually matching is then used to fine tune the alignment of the cavity contour and Marker points.

Results:

The standard applicator scans have shown to agree well with the applicators in the patient scans. The time taken to register the scans has shown to be less than generating the cavities using the standard methods of contouring on the axial slices or using the dose shaper with sources in the central channel.

Conclusion:

The registration of a standard applicator scan and contour has improved the consistency in the generation of the initial cavity (SAVI) structure. Planning structures used for dose calculation are created with that structure as a starting point so accuracy and consistency are important for dose evaluation and plan comparison.

Ancillary