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

Abstract

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 V95 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, V5, V10, V25, and V30 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 V5 of 25.39% ±3.88% and V20 of 5.66% ±0.89%. The right breast received a mean dose of 2.13±0.22 Gy, with V5 of 1.83% ±1.22% and V10 of 0.04% ±0.12%. The mean dose of unspecified tissue was 5.34±0.37 Gy and V5 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.PACS number: 87.55.‐x, 87.55.D‐, 87.55.dk

Is there a preferred IMRT technique for left‐breast irradiation?

“…The following IMRT techniques were compared: 1) hybrid conventional IMRT, which we currently use routinely in the clinic and which has previously been described in the literature; (11) 2) full conventional IMRT; (6) 3) VMAT (13‐15,17‐19) using RapidArc (Varian Medical Systems, Palo Alto, CA) with two partial arcs, and 4) RapidArc with a previously described technique using six short partial arcs (12) . All techniques are described in detail below in the “Treatment planning” section.…”

“…Six arc RapidArc (6ARC) consisted of six short partial arcs, as described by Tsai et al, (12) irradiating between gantry angles 305°–355°, 355°–45°, 80°–130°, 130°–80°, 80°–30°, and 355°–305°. For each arc, the jaw opening on the side near the chest wall was minimized to reduce the exposure to the left lung and the right breast, resulting in smaller jaw openings than those used in the 2ARC plans.…”

“…Multiple different hybrid, fixed‐beam, and arc‐based IMRT techniques are now available and, depending on the planning criteria, it is plausible that some may perform better than others. Our aim was to take the typical dose distribution of the classic tangent‐based field arrangement as a benchmark and to compare dosimetric characteristics of four previously described IMRT techniques under conditions of free‐breathing, left‐breast irradiation using a simultaneous integrated boost technique (SIB) (6,7,11‐15) . Our primary goal was to investigate their suitability for treatments that stress a reduction in mean and low doses to the heart, lungs, and contralateral breast.…”

The feasibility study of a hybrid coplanar arc technique versus hybrid intensity-modulated radiotherapy in treatment of early-stage left-sided breast cancer with simultaneous-integrated boost

“…The left ventricle was contoured from the mitral valve at the cephalic direction along the smooth appearance of the left ventricular outflow tract, and the posterior border was along the diaphragmatic cardiac surface. [21] NT represents the external contour of the patient's body minus the breast PTV, with an additional distance of 0.5 cm.…”

“…The optimization objectives and relative priorities were the same for all plans [Table 1]. [21] The dose calculation grid was set at 2.5 mm. The skin flash function was not used.…”