Room: Exhibit Hall | Forum 6
Purpose: To investigate the mean doses to the heart, contralateral breast (CB), ipsilateral lung (IL) and contralateral lung (CL) in tangential breast treatments using the Halcyon linac.
Methods: Halcyon is a newly introduced linac with 100% image guidance, allowing a faster turnaround and ensuring accurate setup. The dose from the imaging setup fields is accounted for during treatment planning. In this work, five left and five right tangential breast plans for patients previously treated on a C-arm linac were re-planned for Halcyon. The prescription for all plans was 50 Gy in 25 fractions. The Halcyon plans had the same isocenter and beam configuration as the original plans. Plans were created with the setup imaging techniques available in Halcyon: low-dose or high-quality MV-CBCT and low-dose or high-quality orthogonal MV pairs. Mean doses (D_mean) to the heart, CB, IL and CL were calculated and compared with the D_mean from the C-arm plans.
Results: Low-dose MV-CBCT provided similar imaging dose as orthogonal high-quality MVs, and was selected for the remainder of the study. For right-sided plans, the D_mean in the C-arm linac was 0.42Â±0.10, 0.24Â±0.02, 6.19Â±1.16 and 0.03Â±0.03 Gy for the heart, CB, IL and CL, respectively, while values in the Halcyon plans were 1.30Â±0.11, 0.68Â±0.11, 7.45Â±1.20 and 0.43Â±0.14. For left-sided treatments, D_mean in the C-arm linac plans was 0.84Â±0.27, 0.13Â±0.07, 4.27Â±1.71 and 1.13Â±0.61 Gy for the heart, CB, IL and CL, respectively while for the Halcyon plans values were 1.80Â±0.31, 0.62Â±0.16, 5.15Â±1.59 and 0.60Â±0.20 Gy. More than 70% of the dose to the CB and CL were attributable to the imaging fields.
Conclusion: D_mean to OARs in Halcyon treatments using the MVCBCT low dose technique are lower than mean doses reported from other techniques such as VMAT or IMRT. D_mean to OARs can be further decreased by implementing imaging dose reduction techniques.