Calypso® and laser-based localization systems comparison for left-sided breast cancer patients using deep inspiration breath hold

S. Robertson,1 D. Kaurin,1,2 J. Kim,2,3 L. Fang,2,3 L. Sweeney,1,2 K. Halloway,2 A. Tran2,3
1Northwest Medical Physics Center, Lynnwood, WA; 2Seattle Cancer Care Alliance, Seattle, WA; 3University of Washington Medical Center, Seattle, WA

AAPM Annual Scientific Meeting, Austin, TX (2014).

Purpose: Our institution uses a manual laser-based system for primary localization and verification during radiation treatment of left-sided breast cancer patients using deep inspiration breath hold (DIBH). This primary system was compared with sternum-placed Calypso(R) beacons (Varian Medical Systems, CA). Only intact breast patients are considered for this analysis.

Methods: During computed tomography (CT) simulation, patients have BB and Calypso(R) surface beacons positioned sternally and marked for free-breathing and DIBH CTs. During dosimetryplanning, BB longitudinal displacement between free breathing and DIBH CT determines laser mark (BH mark) location. Calypso(R) beacon locations from the DIBH CT are entered at the Tracking Station. During Linac simulation and treatment, patients inhale until the cross-hair and/or lasers coincide with the BH Mark, which can be seen using our high quality cameras(Pelco, CA). Daily Calypso(R) displacement values (difference from the DIBH-CT-based plan) are recorded.The displacement mean and standard deviation was calculated for each patient (77 patients, 1845 sessions). An aggregate mean and standard deviation was calculated weighted by the number of patient fractions.Some patients were shifted based on MV ports. A second data set was calculated with Calypso(R) values corrected by these shifts.

Results: Mean displacement values indicate agreement within 1±3mm, with improvement for shifted data (Table).

Conclusion: Both unshifted and shifted data sets show the Calypso(R) system coincides with the laser system within 1±3mm, demonstrating either localization/verification system will result in similar clinical outcomes. Displacement value uncertainty unilaterally reduces when shifts are taken into account.