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

Abstract

PURPOSE\nBreast 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\xa0kVp X-ray source, respectively. For three comparable applicator sizes with volume differences <11%, we compare the dosimetry using clinical planning data.\n\n\nMETHODS AND MATERIALS\nA dosimetric comparison between the INTRABEAM and Axxent to the proximal 1.0\xa0cm 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\xa0cm from the applicator surface was also computed.\n\n\nRESULTS\nThe mean DVPs were 5.5 ± 0.8% V90, 12.1\xa0±\xa01.5% V80, 47.5\xa0±\xa05.8% V50, 6.4\xa0±\xa00.6\xa0Gy Dmin, and 3.2\xa0±\xa00.3 HI for the INTRABEAM applicators compared with 7.4\xa0±\xa00.3% V90, 14.7\xa0±\xa00.8% V80, 55.2\xa0±\xa04.7% V50, 4.0\xa0±\xa00.6\xa0Gy Dmin, and 6.4\xa0±\xa01.1 HI for the Axxent applicators. INTRABEAM skin doses ranged from 7.7 to 9.0\xa0Gy\xa0at 0.7\xa0cm to 5.5-6.8\xa0Gy\xa0at 1.0\xa0cm, whereas Axxent skin doses ranged from 10.7 to 13.0\xa0Gy\xa0at 0.7\xa0cm to 7.8 to 9.3\xa0Gy\xa0at 1.0\xa0cm.\n\n\nCONCLUSIONS\nWe demonstrated ±5% comparable dosimetric coverage for tissue ≤0.5\xa0cm from the cavity and higher skin dose for Axxent plans. The DVPs increased with applicator size and with stepped treatment delivery.