RESUMEN
Objective:To compare the dosimetric characteristics of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) after left breast conserving surgery.Methods:Twenty-four patients with left breast cancer after breast-conserving surgery who were admitted to the Department of Radiation Oncology of Tumor Hospital of Yunnan Province from May 2016 to May 2019 were selected. The HT plan and the VMAT plan were designed for the same patient. The target dose and the dose volume parameters of organs at risk were compared and analyzed in the two radiotherapy plans.Results:There were significant differences in the D 2% [(59.68±0.46) Gy vs. (60.06±0.20) Gy, t=-4.229, P<0.001], D 98% [(57.46±0.44) Gy vs. (57.20±0.07) Gy, t=2.912, P<0.001], conformity index (CI) (0.80±0.05 vs. 0.76±0.04, t=4.079, P<0.001) and homogeneity index (HI) (0.04±0.01 vs. 0.05±0.00, t=-5.505, P<0.001) of the planning gross tumor volume (PGTV) between the HT and VMAT plans. However, there was no significant difference in the D 50% [(58.77±0.46) Gy vs. (58.75±0.11) Gy, t=0.179, P=0.859]. There were significant differences in the D 50% [(51.99±0.39) Gy vs. (52.39±0.36) Gy, t=-5.278, P<0.001], D 98% [(49.46±0.29) Gy vs. (48.35±0.46) Gy, t=9.538, P<0.001] and HI (0.19±0.01 vs. 0.21±0.01, t=-7.538, P<0.001) of the planned target volume (PTV) between the two plans. However, there were no significant differences in the D 2% [(59.13±0.64) Gy vs. (59.09±0.46) Gy, t=0.511, P=0.614] and CI (0.83±0.04 vs. 0.82±0.04, t=1.637, P=0.115). In terms of organs at risk, there were significant differences in the V 5 [(57.90±1.42)% vs. (52.40±5.74)%, t=4.812, P<0.001], V 20 [(22.40±2.17)% vs. (18.40±3.16)%, t=5.573, P<0.001] and D mean [(12.71±0.55) Gy vs. (11.46±1.26) Gy, t=4.963, P<0.001] of left lung, D mean of right lung [(3.42±0.27) Gy vs. (2.49±0.24) Gy, t=13.310, P<0.001], D mean of right breast [(4.41±0.50) Gy vs. (3.12±0.65) Gy, t=10.326, P<0.001], V 30 [(0.55±0.37)% vs. (1.24±1.11)%, t=-4.020, P=0.001] and D mean of heart [(4.68±0.62) Gy vs. (3.83±0.88) Gy, t=7.335, P<0.001], D mean of left atrium [(2.53±0.31) Gy vs. (2.16±0.28) Gy, t=5.488, P<0.001], D mean of right atrium [(2.77±0.43) Gy vs. (2.20±0.30) Gy, t=7.103, P<0.001], D mean of right ventricle [(5.10±0.72) Gy vs. (3.72±0.94) Gy, t=9.802, P<0.001] and D 2% of spinal cord [(14.79±2.73) Gy vs. (5.42±2.23) Gy, t=14.788, P<0.001] between HT and VMAT plans. There was no significant difference in the D mean of left ventricle [(5.10±1.19) Gy vs. (4.80±1.54) Gy, t=1.250, P=0.224]. Conclusion:Both the HT plan and the VMAT plan can meet the treatment requirements. The HT plan can provide better target area conformity and dose uniformity. The VMAT plan has more advantages in terms of organs at risk. The HT plan shows an advantage only in exposure to high-dose area.