Room: ePoster Forums
Purpose: Breast Intraoperative Radiation Therapy (IORT) has become increasingly popular because of the development of two commercial electronic brachytherapy treatment systems, the Zeiss Intrabeam and Xoft Axxent. Both systems utilize 50 kVp x-rays to deliver 20 Gy to the surface of the lumpectomy bed, but the details of delivery vary between the two machines. We compare the dose-volume data from two electronic brachytherapy sources for breast IORT.
Methods: We define a PTV as a 1 cm expansion around the applicator to evaluate dosimetric parameters and dose fall-off. We compare PTV V90, V80, V50, Dmin and Heterogeneity Index (HI) for implanted devices between 30 to 65 cc (i.e. common sizes) using measured and vendor provided treatment parameters. Skin dose was computed as a function of skinbridge for 7 to 10 mm. Xoft Axxent DVH data was computed in Varian BrachyVision using TG-43 parameters, while Zeiss Intrabeam data was computed from provided PDD data assuming a perfectly spherical applicator with no anisotropy corrections. HI was calculated as Dmax/Dmin.
Results: The mean dose-volume parameters for the Intrabeam system are 6.3Â±1.0% (V90), 13.5Â±1.8% (V80), 49.5Â±6.1% (V50) and HI is 3.25Â±0.34 compared to 5.3Â±1.1% (V90), 11.7Â±1.4% (V80), 47.8Â±1.8% (V50) and HI is 6.78Â±0.70 for the Axxent. Intrabeam skin doses range from: 7.73-8.99 (7 mm), 6.87-8.22 (8mm) and 6.16-7.49 (> 9mm) Gy for the Intrabeam. Axxent skin doses range from 10.74-12.98 (7mm), 8.73-11.29 (8mm), and 7.93-10.92 (9mm) Gy. Larger applicators delivered greater doses to the skin.
Conclusion: HI and skin dose for the Axxent system are higher because it considers anisotropy, while the Intrabeam system assumes uniform dose distribution. Skin dose increases with applicator size and plateaus for distances greater than 9 mm.