Multicatheter interstitial brachytherapy versus stereotactic radiotherapy with CyberKnife for accelerated partial breast irradiation: a comparative treatment planning study with respect to dosimetry of organs at risk
Purpose: To dosimetrically compare multicatheter interstitial brachytherapy (MIBT) and stereotactic radiotherapy with CyberKnife (CK) for accelerated partial breast irradiation (APBI) especially concerning the dose of organs at risk (OAR-s).
Methods: Treatment plans of thirty-two MIBT and CK patients were compared. The OAR-s included ipsilateral non-target and contralateral breast, ipsilateral and contralateral lung, skin, ribs, and heart for left-sided cases. The fractionation was identical (4 x 6.25 Gy). Relative volumes receiving a given dose (e.g. V100) and doses delivered to small volumes (eg. D1cm3) were calculated from dose-volume histograms and related to prescribed dose (25 Gy).
Results: Regarding non-target breast CK performed slightly better than MIBT (V100: 0.7% vs. 1.6%, V50: 10.5% vs. 12.9%). The mean dose of the ipsilateral lung was the same for both techniques (4.9%), but doses irradiated to 1cm3 were lower with MIBT (36.1% vs. 45.4%). Skin and rib protection was better with MIBT. There were no significant differences between the dose-volume parameters of the heart, but with MIBT, slightly larger volumes were irradiated by a small dose (V5: 29.9% vs. 21.2%). Contralateral breast and lung received a slightly higher dose with MIBT (D1cm3: 2.6% vs. 1.8% and 3.6% vs. 2.5%).
Conclusion: Both techniques can properly irradiate the target volume and the dose distributions are very similar with a high conformity. CK protected the non-target breast, heart, and contralateral organs more, while the nearby organs (skin, ribs, ipsilateral lung) received less dose with MIBT. More studies are needed to analyze whether these dosimetrical findings have clinical significance.
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