SAVI catheter digitization impact: A single institution multiuser uncertainty study

To assess the impact of Strut Adjusted Volume Implant (SAVI) catheter digitization variability on dosimetric evaluation parameters of HDR breast brachytherapy treatment plans. Four clinically approved SAVI cases were chosen for this digitization variability analysis. All patients were implanted with 6-1 SAVI device. Six experienced physicists independently digitized SAVI catheters. Plans utilizing significant peripheral loading were used for this study where SAVI catheters were near the chest wall and/or skin. After digitization was completed for each case by each physicist, the original clinical dwell times were copied over for comparison. This ensured that only variability among plans is the digitization of SAVI catheters by different users. The original plan that went through two physicists' checks and one physician's review was considered the "ground truth" plan to which all other plans were compared. Plans were evaluated on planning parameters for lumpectomy cavity's PTV_Eval D90, V150, V200 and for the OARs (Chest-Wall/Ribs and Skin), on D_0.03cc, D_0.1cc, D_1cc, D_2cc. Additionally, a visualization window setting-based uncertainty test was performed on the same 4 cases. Our results showed that the average and maximum dwell positional digitization uncertainties were 0.36 and 0.75 mm, respectively. Average PTV_Eval D90 was 97.11+/-2.93 %, V150 was 23.10+/-4.25 cc, V200 was 11.88+/-1.93 cc. All OAR constraints were met on all plans - Chest-Wall/Ribs (CW/Ribs) and Skin D_0.03cc was 103.40+/-9.23 % and 93.60+/-6.14 %, respectively. Aggregate analysis across all plans shows a clinically nonsignificant spread around the mean for all parameters considered. The robustness of SAVI treatment plans to minor variation in catheter digitization was proved through our multiuser study. Our study showed that SAVI planning constraints are stable within reasonable variation of digitization differences. Such uncertainty analysis is useful in standardization of digitization practices in a department and in defining action levels on digitization fixing request during a 2nd check.