Dosimetric comparison between two volumetric modulated photon arc therapies for patients with breast cancer mastecomy

Objective To compare the dosimetry and treatment efficiency between a multi-ple partial volumetric-modulated arcs therapy (MP-VMAT)and double-arc volumetric modulated arc therapy (DA-VMAT)for patients with breast cancer mastecomy.Methods 19 patients with breast cancer treated by mastecomy and requiring postoperative radiotherapy were collected.MP-VMAT and DA-VMAT plans were applied for each patient respectively.Dosimetry parameters for target volume and organ of risks (OARs)were compared.Machine unite and delivery times were compared.Results MP-VMAT plans had a more uniform target dose distribution with average Conformation Index (CI )andHomogeneity Index (HI )of0 .5 6 and 1 .0 6 compared to 1 .0 6 and 1.14 of the DA-VMAT plans(P <0.05).MP-VMAT plans predicted a reduction of 5.53% in V20 of contralateral lung,3.74 Gy in mean dose,6.27% in V5 and 5.53% in V20 of ispleratal lung respectively (P <0.05).MP-VMAT plans predicted a reduction of 10.33% and 7.82% in V5 and V10 of heartrespectively (P <0.05),MP-VMAT plans predicted a reduction of 9.14%, 2.72% and 0.06% inV5,V10 and V15 of contralateral breast respectively (P <0.05)plans. However,MP-VMAT plans improved monitor units 7 4 5 .9 MU and treatment time 3 0 4 .6 s compared with DA-VMAT 524.4 MU and 196.7 s (P <0.05).Conclusion MP-VMAT plans generate more uniformity in the target dose and decreased the dose of most of organs of risk com-pared to the DA-VMAT,But improved monitor units and treatment time.In clinical application, different techniqies are chosen based on the situation of every patient.