Program Information
Dosimetric Comparison of VMAT Vs 3D Conformal for Left Breast Plans
J Bogue*, J Wan , E Parsai ,University of Toledo Medical Center, Toledo, OH, R Lavey, Maurer Family Cancer Center
Presentations
TU-C3-GePD-TT-3 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Theater
Purpose: To quantify the dosimetric trade-offs between 3D Conformal and Volumetric Modulated Arc Therapy (VMAT) plans for left breast patients in terms of low and prescription-dose contributions to organs at risk.
Methods: Nine patients at our institution who were previously treated in the supine position with 3D Conformal or VMAT radiation therapy to the left breast were planned using the alternative method. All treatments delivered a total of 4256cGy in 16 fractions and were normalized to cover 95% of the planned target volume. Conformal plans used non-divergent tangents of mixed energies with gantry angles chosen to minimize the ipsilateral lung, contralateral breast, and heart dose. VMAT plans utilized four 6MV arcs of roughly 260 degrees of arc each and were optimized to meet the constraints set by the physician. Dosimetric comparison was made for the heart, contralateral lung, and contralateral breast based on the mean dose and relative volume receiving 5%, 10%, 20%, 30%, 40%, and 100% of the prescription. The homogeneity index was also calculated to compare dose uniformity throughout the target.
Results: Mean dose and percent volume receiving 5%, 10%, and 20% of the prescription dose increased universally for the heart, contralateral lung, and contralateral breast for VMAT plans, as compared to 3D plans. 3D conformal plans did show a slight increase in relative volume receiving the prescription dose for the contralateral breast and heart, with no difference between the two methods in contralateral lung. VMAT also offered slightly superior homogeneity with a mean homogeneity index of 9.41 as compared to 11.05 for 3D conformal.
Conclusion: Results indicate that VMAT increases mean and low dose volume to the heart, contralateral lung, and contralateral breast, but is better able to spare those structures from prescription dose while delivering a more homogenous dose distribution.
Contact Email: