Effect of respiratory amplitude on the dose distribution of volumetric modulated arc therapy

Abstract

Objective To study the effect of the respiratory amplitude on the dose distribution of volumetric modulated arc therapy (VMAT). Methods Respiratory motion simulation phantom (QUASAR) was used to simulate the respiratory movement from head to toe, and a two-dimensional ionization chamber matrix was used to collect the dose distribution in isocenter with different respiratory amplitude. Verisoft software and absolute dose analysis were used to analyze dose distribution, percentage errors of absolute dose in isocenter, passing rates of radiation field for the data collected, and results were compared to planned dosage. Results The effect on isocenter target dose of respiratory motion was below dose tolerance 5% (t=-22.614--10.756, P<0.05). The respiratory movement made the dose on the edge of the target area higher, with fewer hot spots and more cold spots in the target area. As the respiratory amplitude increased, the effect of respiratory movement on the overall dose distribution in the target area was greater. The difference of the whole beam γ passing rate between 6, 8, 10 mm and stationary state was significant (t=3.095, 8.685, 14.096, P<0.05). The difference of target γ passing rate between 8, 10 mm and stationary state was significant (t=6.081, 9.841, P<0.05). Conclusions The respiratory movement could cause the dose transmission errors of VMAT, the error increased with increased range of motion. The actual radiation dose for normal tissues along the direction of respiratory movement on the target edge was higher than what was planned. Key words: Respiratory movement amplitude; Volumetric modulated arc therapy (VMAT); Dose distribution; Respiratory motion simulation phantom (QUASAR)