Evaluation of safety by skin dosimetry in Intraoperative Radiotherapy for breast cancer patients

We investigated the safety of Intrabeam™ system, X-ray unit for Intraoperative Radiotheray (IORT) by measuring surface dose using Optically Stimulated Luminescent Dosimeter(OSLD). 30 patients were selected, who were in breast cancer patients and had an operation of breast conserving surgery (BCS). At the inner surface of tumor bed, 20 Gy were described, and 5 Gy at 1cm depth from the inner surface. Along the size of tumor bed which could be decided after resection of tumor, the size of applicator were determined. Usual treatment time were from 18 to 40 minutes. For the measurement of surface doses, OSLD were placed at superior(U1,2), inferior(D1,2), lateral(L1,2) and medial(M1,2) directions from the center of applicator. Each direction, two OSLD were placed at 0.5 cm and 1.5 cm from the center. Mean, maximum, and minimum doses were analyzed to be compared. Mean values were U1 2.23±0.80 Gy, U2 1.54±0.53 Gy, D1 1.73±0.63 Gy, D2 1.25±0.45 Gy, L1 1.95±0.82 Gy, L2 1.38±0.42 Gy, M1 2.03±0.70 Gy, and M2 1.51±0.58 Gy. Maximum values were 4.34 Gy at U1, and Minimum values were 0.45 Gy at M2. 13.3 % of patient (4pts out of 30) were reported that surface dose were over 4 Gy. The fact that skin dose of all patients were less than 5 Gy based on OSLD measurement showed the safety of Intrabeam™ system. In the relatively small breast volume, the tendency that surface dose was increased had been shown, which was analyzed by the data of patients who irradiated over 4Gy at skin surface. Therefore, for appropriate indication for IORT, it is suggested that breast volume as well as the size and position of tumor should be carfully considered