SU‐GG‐T‐488: Dosimetric Parameter Comparison of the Electronic Tissue Compensator Technique with the Conventional Physical Wedge Technique for the Whole Breast Treatment

Abstract

Purpose: To compare a dosimetric benefit between electronic tissue compensator (ETC) technique and the conventional physical wedge (PW) technique for a whole breast (WB) tangential field irradiation treatment. Method and Materials: 17 breast cases, with chest wall separation 16 to 26 cm at normalization point slice, were included in this study. Eclipse Planning System (V7.3) was used to generate a plan. The plan remained with a same beam setup, beam weighting, normalization point, and energy (6MV or 6MV mixed with 18MV) in both technique for each case. The breast tissue was outlined as a planning target volume (PTV). For a PTV dose coverage information, PTV encompassed by 95% isodose line (V95) and PTV received the minimum dose (Dmin) were studied. To examine a high dose region, a PTV received at least 105% prescription dose (V105) was computed. To study dose inhomogeneity (DI) in the PTV, a ratio of the difference of Dmax and Dmin to the prescription dose was estimated. In additional, a total MU from each plan was recorded to not only measure the linac beam on time, but also as a factor for the machine scatter and leakage evaluation. Results: By comparing with the PW plan, (1) The PTV coverage, V95, showed quite similar (difference within 0.5%) in both techniques and Dmin was lower on a percentage of 1.2±9.1 from ETC plan; (2) The hotspot, V105, was reduced by a percentage of 2.9±2.2 in ETC plan. (3) DI was decreasing by a percentage of 1.3±12.3 in ETC plan. The total MU reduced by about 8.9±17.1 percent in ETC plan. Conclusion: ETC technique presented a dosimetric benefit for the WB tangential field treatment. And these benefits were subjected to case‐by‐case study. A careful comparison is needed for the treatment plan selection.