ABSTRACT
Objective:To explore the dosimetry difference between volumetric modulated arc therapy (VMAT) and tomo direct (TD) in tumor bed simultaneous push radiotherapy after left breast-conserving surgery, and to provide more dosimetry reference for clinic.Methods:A total of 22 patients with left breast cancer who underwent simultaneous quantitative radiotherapy after breast-conserving surgery were selected from the Department of Radiation Oncology, Yunnan Cancer Hospital from December 2018 to June 2020. The localized CT images and target organs at risk and other structural data were collected. Two radiotherapy plans, VMAT and TD, were designed for the same patient, and the dosimetry differences of target areas and organs at risk were compared and analyzed between the two groups.Results:In terms of target dosimetry, there were statistically significant differences in the D 2% [ (59.99±0.19) Gy vs. (59.55±0.51) Gy, t=4.09, P<0.001], D 98% [ (57.19±0.08) Gy vs. (57.46±0.22) Gy, t=-5.10, P<0.001], conformal index (CI) (0.76±0.05 vs. 0.58±0.13, t=8.19, P<0.001) and homogeneity index (HI) (0.05±0.00 vs. 0.04±0.01, t=4.89, P<0.001) of the planning gross tumor volume (PGTV) between VMAT and TD plans. However, there was no statistically significant difference in the D 50% [ (58.73±0.10) Gy vs. (58.73±0.24) Gy, t=-0.03, P=0.974]. There were statistically significant differences in the D 50% [ (52.21±0.33) Gy vs. (53.00±0.72) Gy, t=-4.81, P<0.001], D 98% [ (48.44±0.43) Gy vs. (49.09±0.21) Gy, t=-6.80, P<0.001], CI (0.83±0.06 vs. 0.67±0.06, t=10.52, P<0.001) and HI (0.20±0.01 vs. 0.19±0.01, t=8.75, P<0.001) of the planned target volume (PTV) between the two plans. However, there was no statistically significant difference in the D 2% [ (59.01±0.45) Gy vs. (59.00±0.48) Gy, t=0.22, P=0.830]. In terms of organs at risk, there were statistically significant differences in the V 20 [ (18.81±2.86) % vs. (22.03±1.91) %, t=-5.36, P<0.001] and D mean [ (11.66±1.32) Gy vs. (12.85±1.46) Gy, t=-4.10, P=0.007] of left lung, V 5 [ (5.70±2.90) % vs. (0.30±0.13) %, t=16.44, P<0.001] and D mean [ (2.45±0.29) Gy vs. (0.43±0.14) Gy, t=9.09, P<0.001] of right lung, D mean [ (3.22±0.72) Gy vs. (1.69±0.80) Gy, t=5.41, P<0.001] of right breast, D 2% [ (5.37±1.97) Gy vs. (0.46±0.09) Gy, t=11.75, P<0.001] of cord between VMAT and TD plans. There were no significant differences in the V 5 of left lung [ (53.00±5.99) % vs. (50.00±7.69) %, t=1.91, P=0.061], V 5 of right breast [ (11.51±4.60) % vs. (8.06±3.49) %, t=1.59, P=0.120], V 30 [ (1.49±0.69) % vs. (1.51±0.71) %, t=-0.06, P=0.952] and D mean [ (3.99±0.97) Gy vs. (3.90±1.03) Gy, t=0.56, P=0.581] of heart between the two plans. Conclusion:TD and VMAT can meet the clinical dosimetry requirements for patients with left breast cancer after breast-conserving surgery. However, the two techniques have their own characteristics. VMAT has better conformity and TD has better uniformity. TD is significantly better than VMAT in protecting the right lung, right breast and spinal cord of healthy organs at risk. VMAT is better in protecting the left lung. Both VMAT and TD basically achieve the same protection for heart.
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 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.