Session Item

To dosimetrically compare stereotactic radiotherapy with CyberKnife (CK) and multicatheter insterstitial brachytherapy (MIBT) for accelerated partial breast irradiation, focusing on the dose to organs at risk (OARs).

Treatment plans of thirty-one MIBT treated patients were selected, and CK plans were created on the same CT images. The OARs were the same for both plans of every patient: ipsilateral non-target and contralateral breast, ipsilateral and contralateral lung, skin, ribs and heart for left sided cases. The CTV was created from the outlined lumpectomy cavity with a total margin (surgical + radiation) of 20 mm in six main directions. The PTV was equal to CTV for MIBT, but in CK plans it was generated from CTV with the addition of a 2 mm isotropic margin for real-time marker tracking. The fractionation was identical (4 x 6.25 Gy). Dose-volume parameters were calculated for both techniques and compared using a Wilcoxon matched pair test.

Regarding dose coverage, both techniques performed well, the D90 parameter was similar, but the V100 parameter was lower for MIBT than CK, V100 91.6% vs. 98.9%, p<0.001, respectively. Regarding the V100 of non-target breast the CK performed slightly better than the MIBT (V100: 1.1% vs. 1.6%), but for V90, V50 and V25 the MIBT resulted in less dose. The average dose of ipsilateral lung was lower for MIBT than for CK, 4.9% vs. 6.2%, p<0.001, respectively. For the heart, only the D_2cm3 parameter was significantly lower for MIBT (17.3% vs. 20.4%, p=0.0311 for MIBT and CK, respectively). For all of the examined parameters of skin and ribs, the MIBT performed better. The dose to contralateral breast and lung was very low for both techniques, the MIBT performed better for contralateral lung (D_1cm3 3.8% vs. 6.1%, p<0.001 for MIBT and CK, respectively), but no significant differences were found for the contralateral breast.

The target volume can be properly irradiated by both techniques with high conformity. MIBT provides more advantageous plans than CK regarding the OARs, except for the dosimetry of heart and contralateral breast and for dose conformity, but all of the OAR parameters for CK are also below the dose limits.