VMAT versus TOMO in dosimetric parameters for treatment of middle thoracic esophageal cancer

Objective To compare the dose distribution of volumetric modulated arc therapy (VMAT) versus tomotherapy (TOMO)for treatment of middle thoracic esophageal cancer patients, and provide basis for clinical decision. Methods Nineteen male patients with middle thoracic esophageal cancer who had not undergone esophageal surgery in our hospital from 2015 to 2017 were enrolled in this study. For each patient, the target and organs at risk (OAR) were delineated with the same criterion before VMAT and TOMO plans were designed. All dosimetric parameters of two plans were analyzed and compared by dose volume histogram (DVH). Results There were statistically significant differences in gross tumor volume (GTV) and planning target volume (PTV)between VMAT and TOMO (all P < 0.05), including GTV-D2(6 810.47±23.18) cGy vs (6 723.97±17.47) cGy, PTV-D2(6 765.93±53.94) cGy vs (6 656.61±23.18) cGy, GTV-D50(6 664.94±33.83) cGy vs (6 600.40±3.56) cGy, PTV-D50(6 113.57±188.91) cGy vs (5 954.81±29.64) cGy, GTV-Conformity index (GTV-CI)(48.42±11.14)% vs (63.16±8.11)%, PTV-CI(68.37±5.04)% vs (75.47±4.31%), GTV-Heterogeneity index (GTV-HI)(4.84±0.96)% vs (3.63±0.50)% and PTV-HI(23.05±1.31)% vs (21.68±0.49)%. However, no significant difference was found in GTV-D98(6 480.54±55.61) vs (6 487.91±27.38) cGy and PTV-D98(5 353.01±71.90) cGy vs (5 362.62±20.39) cGy (P> 0.05, respectively). As for OAR of lung, VMAT had lower left lung V5(68.05±4.13)% vs (79.47±7.79)%, left lung Dmean(1 290.71±92.73) cGy vs (1 368.53±141.50) cGy, right lung V5(66.53±4.21)% vs (78.54±8.70)%, right lung Dmean(1 264.59±109.66) cGy vs (1 344.32±98.61) cGy, double lung V5(67.11±3.80)% vs (79.14±8.25)% and double lung Dmean(1 290.71±98.61) cGy vs (1 368.53±95.92) cGy(all P < 0.05). However, VMAT achieved higher left lung V30(10.42±2.57)% vs (8.66±2.62)%, right lung V30(9.79±2.15)% vs (8.70±1.30)% and all lung V30(10.42±1.30)% vs (8.66±1.40)% compared to TOMO (all P < 0.05). Nevertheless, there was no significant difference in left lung V20(21.79±1.96)% vs (22.01±3.08)%, right lung V20(20.11±3.33)% vs (20.02±1.97)% and double lung V20(21.79±1.97)% vs (22.01±1.82)% between two techniques (all P > 0.05). Compared with VMAT, TOMO provided a superior protection for heart V30 and V40(16.63±4.47)% vs (12.96±3.20)%, (7.21±1.69)% vs (6.07±1.88)%, P < 0.05, respectively but failed to heart Dmean(1 832.32±394.64) cGy vs (1 836.37±533.59) cGy, P > 0.05. Spinal cord D2 was lower in TOMO than in VMAT(4 041.87±111.8) cGy vs (3 755.48± 229.33) cGy, P < 0.05. Conclusion Both VMAT and TOMO meet with the middle thoracic esophageal cancer patients' treatment needs, but TOMO further improves target's Conformity index (CI) and heterogeneity index (HI). Each of them has their own advantages for OAR sparing. Thus, radiotherapy techniques choosing should depend on patient's condition.