Dosimetric comparison between interstitial brachytherapy and volumetric-modulated arc therapy for tumor bed boost in breast cancer

PURPOSE: To dosimetrically compare high-dose-rate interstitial brachytherapy (HDR-BT) with volumetric-modulated arc therapy (VMAT) for tumor bed boost, following breast conservative treatment. MATERIAL AND METHODS: 50 patients with early-stage breast cancer who underwent breast conservation surgery, followed by either HDR-BT (n = 25) of 15 Gy in 6 fractions over a period of 3 days, or VMAT dose of 16 Gy in 8 fractions (n = 25) for tumor bed boost, were retrospectively reviewed. All patients received whole breast irradiation of 46 Gy in 23 fractions. Dosimetric parameters for organs at risk (OARs), including ipsilateral and contralateral lungs, heart, contralateral breast, skin, and ribs, were evaluated with the help of dose-volume histograms (DVH). RESULTS: Heart sparing was similar in both modalities (left-sided breast irradiation, HDR-BT D(2cc) 20.5% vs. VMAT 30.2%, p-value = 0.243; right-sided breast irradiation, D(2cc) 6.5% vs. 4.4%, p-value = 0.165). Left-sided cases received higher dose to heart compared to right-sided patients. Interstitial brachytherapy resulted in significantly less dose to contralateral breast (D(2cc) 4.3% vs. 9.6%, p-value < 0.0001), ipsilateral lung (D(2cc) 27.6% vs. 73.2%, p-value < 0.0001), contralateral lung (D(2cc) 4.2% vs. 14.5%, p-value < 0.0001), ribs (D(2cc) 24.1% vs. 41.2%, p-value < 0.0001), and skin (D(2cc) 77.3% vs. 95%, p-value < 0.0001). CONCLUSIONS: HDR-BT-based tumor bed boost irradiation results in significantly lower doses to most organs at risk with similar heart sparing compared to VMAT.