Abstract
Background: The purpose of this study was to compare the dosimetric differences in helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) plans of bilateral breast cancer after modified radical mastectomy.Methods: Ten patients with synchronous bilateral breast cancer (SBBC) who received modified radical mastectomy were selected for study. Two radiotherapy treatment plans, including HT and VMAT, were created for each patient. The prescribed doses of bilateral breast cancer and dual target volumes were given 25 times at 50Gy. The dosemetric parameters of planning target volume (PTV) and organs at risk (OARs) between HT and VMAT plans were compared and evaluated. Results: For PTV, HT had a higher V95 than that of VMAT plans (99.23 ± 0.61 % vs 98.17± 1.08 %, p=0.024). The conformity index (CI) between two techniques was statistically equivalent (0.812 ± 0.03 vs 0.793 ± 0.04, p=0.322) and the homogeneity index (HI) was reduced from 0.127 to 0.105 (p=0.007) when compared with that of VMAT. For OARs, HT had significantly lower Dmax for spinal cord and V5 for heart when compared with those of VMAT plans (16.68 Gy and 20.93% vs 38.82 Gy and 30.26%, respectively) (p<0.001). HT plans showed significantly lower V5, V10 and V20, that resulted in lower Dmean for the lungs (13.38 Gy vs 14.28Gy, p=0.013). However, VMAT showed specific advantages on V10, V20 and V30 for the heart and V5 and V10 for the liver when compared with those of HT plans (p<0.01). The Dmean for the heart and liver between the two techniques was not significantly different (p>0.05). HT plans also showed greater monitor units (MUs) and beam on time. Conclusion: HT had better PTV coverage and HI and showed better protections for the spinal cord and lungs compared with those of VMAT plans. HT plans effectively reduced the low-dose volume (V5) of the heart, while VMAT plans reduced V10, V20 and V30 for the heart. Both HT and VMAT plans exhibited similar Dmean for the heart and liver. The treatment efficiency of VMAT is higher than that of HT plans, and therefore, physicians need to choose a reasonable radiotherapy plan according to patient's conditions.