The feasibility study of using multiple partial volumetric-modulated arcs therapy in early stage left-sided breast cancer patients.

The purpose of this study was to assess the feasibility of using a multiple partial volumetric-modulated arcs therapy (MP-VMAT) technique on the left breast irradiation and to evaluate the dosimetry and treatment efficiency. Ten patients with left-sided breast cancer who had been treated by whole breast irradiation were selected for the treatment plan evaluation by using six partial volumetric modulated arcs. Each arc consisted of a 50° gantry rotation. The planning target volumes and the normal organs, including the right breast, the bilateral lungs, left ventricle, heart, and unspecified tissue, were contoured on the CT images. Dose-volume histograms were generated and the delivery time for each arc was recorded. The PTV received greater than 95% of the V(95) for all cases, and the maximum dose was within ± 1% of 110% of the prescription dose. The mean homogeneity index (HI) was 10.61 ± 0.99, and mean conformity index (CI) was 1.21 ± 0.03. The mean dose, V(5), V(10), V(25), and V(30) of the heart were 7.61 ± 1.38 Gy, 59.73% ± 15.87%, 24.39%± 6.82%, 2.52%± 1.11%, and 1.57% ± 0.71%, respectively. The volume of the left ventricle receiving 25 Gy was 5.15% ± 2.23%. The total lung mean dose was 5.57 ± 0.36 Gy, with V(5) of 25.39% ± 3.88% and V(20) of 5.66% ± 0.89%. The right breast received a mean dose of 2.13 ± 0.22 Gy, with V(5) of 1.83% ± 1.22% and V(10) of 0.04% ± 0.12%. The mean dose of unspecified tissue was 5.34 ± 0.37 Gy and V(5) was 22.23% ± 1.57%. The volume of the unspecified tissue receiving 50 Gy was 0.50% ± 0.14%. The mean delivery time for each arc was 13.9 seconds. The average MU among ten patients was 511 MU (range 443 to 594 MUs). The MP-VMAT technique for the left-sided breast cancer patients achieved adequate target dose coverage while maintaining low doses to organs-at-risk, and therefore reduced the potential for induction of second malignancy and side effects. The highly efficient treatment delivery would be beneficial for improving patient throughput, providing patient comfort, and achieving precise treatment with the breathing control system.