Abstract:

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 V₅ [(57.90±1.42)% vs. (52.40±5.74)%, t=4.812, P<0.001], V₂₀ [(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], V₃₀ [(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.

Key words: Unilateral breast neoplasms, Breast conserving surgery, Helical tomotherapy, Volumetric modulated arc therapy, Dosimetry