Dosimetric comparison of the INTRABEAM and Axxent for intraoperative breast radiotherapy.

Purpose: Breast intraoperative radiotherapy with electronic brachytherapy (eBT) sources, such as the Zeiss INTRABEAM and the Xoft Axxent, are used to treat the lumpectomy cavity using a stationary or a stepped 50 kVp X-ray source, respectively. For three comparable applicator sizes with volume differences <11%, we compare the dosimetry using clinical planning data. Methods and materials: A dosimetric comparison between the INTRABEAM and Axxent to the proximal 1.0 cm of tissue surrounding the applicator is performed using dose-volume parameters (DVPs): V90, V80, V50, Dmin, and Homogeneity Index (HI); HI was calculated as Dmax/Dmin. The dose-volume histograms of the INTRABEAM and Axxent were computed with measured percent depth dose data and with TG-43 parameters, respectively. The skin dose of 0.7-1.0 cm from the applicator surface was also computed.

Results: The mean DVPs were 5.5 ± 0.8% V90, 12.1 ± 1.5% V80, 47.5 ± 5.8% V50, 6.4 ± 0.6 Gy Dmin, and 3.2 ± 0.3 HI for the INTRABEAM applicators compared with 7.4 ± 0.3% V90, 14.7 ± 0.8% V80, 55.2 ± 4.7% V50, 4.0 ± 0.6 Gy Dmin, and 6.4 ± 1.1 HI for the Axxent applicators. INTRABEAM skin doses ranged from 7.7 to 9.0 Gy at 0.7 cm to 5.5-6.8 Gy at 1.0 cm, whereas Axxent skin doses ranged from 10.7 to 13.0 Gy at 0.7 cm to 7.8 to 9.3 Gy at 1.0 cm.

Conclusions: We demonstrated ±5% comparable dosimetric coverage for tissue ≤0.5 cm from the cavity and higher skin dose for Axxent plans. The DVPs increased with applicator size and with stepped treatment delivery.