Dosimetric comparison of the INTRABEAM and Axxent for intraoperative breast radiotherapy

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.

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, D_min, and Homogeneity Index (HI); HI was calculated as D_max/D_min. 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.

The mean DVPs were 5.5 ± 0.8% V₉₀, 12.1 ± 1.5% V₈₀, 47.5 ± 5.8% V₅₀, 6.4 ± 0.6 Gy D_min, 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 D_min, 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.

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.