Optimal PTV Margin in Patients with Fiducial Markers Treated with Accelerated Partial Breast Irradiation (APBI) using 3D-CRT: Final Results of CINJ 040801

Abstract

Fiducial markers are used across disease sites, including prostate cancer, to improve the accuracy of radiation delivery through image-guided radiotherapy. However, there has been little experience with the use of fiducial markers and IGRT in patients with breast cancer. The purpose of this single arm, prospective study was to determine the optimal PTV margin for tattoo, bony anatomy and fiducial marker-based setup in APBI using 3D-CRT. CINJ 040801 is a prospective, single arm trial where at the time of lumpectomy, 4-6 gold fiducial markers were sutured to the walls of the cavity. Patients were treated with a novel fractionation scheme: 4995cGy over 15 once-daily fractions (333cGy/fraction). Treatment volumes and RT planning were based on NSABP/RTOG B-39 guidelines. Patients were setup based on triangulation points of the isocenter based on tattoos and daily pre- and post-RT kV imaging were matched to DRR's based on bony anatomy and fiducial markers, respectively, to determine the inter- and intra-fraction setup variation. A dose calculation software package was developed to simulate the margin size that allows adequate dose coverage. A total of 34 patients were treated on protocol; a total of 32 patients with 461 kV images were available for analysis. The maximum computed margin size that allowed adequate CTV coverage at time of treatment for tattoo, bony anatomy and fiducial marker-based setup was found to be 18.6mm ± 8.8, 20.7mm ± 8.4, 21.3mm ± 7.3 (p = NS) which allows for 90% coverage of the CTV with the prescription dose (V90). Please refer to table 1 for additional margin information. The V90 of the CTV was found to be 98.4 ± 6.7, 99.5 ± 2.2, 99.6 ± 3.2 for tattoo, bony anatomy and fiducial marker-based setup, respectively (p = NS). The V100 of the CTV was found to be 70.4 ± 21.3, 65.7 ± 20.1, and 65.7 ± 20.1, for tattoo, bony anatomy and fiducial marker-based setup, respectively (p = NS). This single arm, prospective study found that a concentric PTV margin of 1.5cm for APBI using 3D-CRT accounts for all inter-and intra-fraction motion for tattoo, bony anatomy and fiducial marker-based setup. Thus, based on these results, the presence of fiducial markers do not allow for PTV margin reduction.Tabled 1Left Side Margin (mm)Right Side Margin (mm)Posterior Side Margin (mm)Anterior Side Margin (mm)Superior Side Margin (mm)Inferior Side Margin (mm)BoneTattooIntraBoneTattooIntraBoneTattooIntraBoneTattooIntraBoneTattooIntraBoneTattooIntraMean18.815.919.519.717.920.729.524.131.215.114.915.319.218.719.521.920.121.5STD5.76.44.77.28.36.611.911.310.711.311.311.07.07.85.47.27.85.1Minimum0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0Maximum40.036.034.038.039.043.059.058.057.041.043.041.041.037.040.046.050.035.0 Open table in a new tab