70P Role of Interstitial Brachytherapy in Early Stage Breast Cancer

Abstract

AimTo assess the quality of high dose rate interstitial implants in breast cancer by using different volumetric indices and to correlate them with skin and subcutaneous tissue toxicities. BackgroundIn recent years brachytherapy by using high dose rate with Ir192 source for partial breast irradiation as well as boost after external irradiation has been an established modality of treatment of early breast cancer. Despite the advantages of brachytherapy with regard to tumor control, maintaining good cosmesis and minimum skin and subcutaneous tissue toxicity is important. Materials and methodsOut of 25 patients, who were selected for interstitial implants after undergoing breast conservation surgery, ten were treated radically with 34 Gy in 10 fractions in 5 days @ 3.4 Gy twice daily and 15 patients received boost dose of 12 Gy in 4 fractions @ 3 Gy twice daily. The median follow up was 20 months. During each follow up assessment of late skin and subcutaneous tissue toxicity as per RTOG criteria was done. Various dosimetric indices were analysed. Dose Volume Histogram for dose per unit volume of skin for 10cc, 5cc, 2cc, 1cc, 0.1cc and 0.01cc was calculated. Best estimates and correlation of toxicity was revealed by assessment of Dose Non-uniformity Ratio (DN R) which also correlated well with geometry defining indices like Uniformity Index (UI). ConclusionVolumetric assessment of skin dose for less than 2 cc correlated most with toxicity. DNR and UI can help us to assess and correlate late skin and subcutaneous tissue toxicity and thus serve useful to determine the quality of implant. DisclosureAll authors have declared no conflicts of interest.