Abstract
Purpose: To quantify the magnitude of dose optimization in 2 opposed tangential‐field IMRT for left whole breast irradiation. Method and Materials: 6 left breast IMRT cases were randomly selected from our recent IMRT group for analysis. Each had 3 plan trials using 2 opposed tangential fields of 6 MV photons with heterogeneity corrections comprise a wedge paired 3D plan, IMRT plan with lung and heart dose constraints, and IMRT plan without organ avoidance (IMRT0). In all trials the prescribed 50.40 Gy conceals 96% of PTV with clinically acceptable dose homogeneities. PTV was defined as entire involved breast with 5 mm margins from skin surface, lung and heart. A smaller volume was used for IMRT optimization due to electron buildups. The global maximum doses, doses at the cardiac surrogate (1 cm cardiac peripheral ring of in the upper‐left quadrant), and volume of the left lung receiving 25.00 Gy dose (V25Gy) were compared. Results: Although global maximum doses were improved from 60.99 ±1.62 Gy in 3D plans to 59.96 ±0.97 Gy in IMRT0 plans, no statistical differences (p ≥ 0.10) were indicated between groups, including IMRT (60.68 ±1.63 Gy) group. Mean doses to cardiac surrogate (12.61 ±6.45 Gy for 3D, 10.77 ±3.68 Gy for IMRT, and 11.83 ±3.08 Gy for IMRT0) were technically undistinguishable. Similar V25Gy for left lung was seen in all 3D, IMRT, and IMRT0 groups (12.8%, 12.5%, and 14.8% respectively). Conclusion: Observed 1.02 Gy in prescribed 50.40 Gy or 1.5% reduction in global maximal dose by IMRT 0 from 3D plans did not reach statistical significance due to limited sample size. With 96% PTV dose coverage and acceptable dose homogeneities, IMRT or IMRT 0 plans did not show meaningful dose sparing for cardiac surrogate or left lung in this investigation.
Published Version
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