Influence of respiratory movement during regional nodal irradiation after mastectomy for breast cancer: an experimental study

Abstract Background This study aimed to evaluate the dosimetric consequences of respiratory movement in postmastectomy radiation therapy (PMRT) including internal mammary nodes (IMNs) between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiation therapy (3D-CRT).Methods An anthropomorphic phantom was used to mimic the chest anatomy of a patient who had undergone mastectomy. Two types of absorbed dose measurements were adopted; a radiochromic film was inserted into a gap between phantom slices at the level of the second IMN and three glass rod dosimeters were placed at the first IMN (IM), chest wall (CW), and left anterior descending (LAD) artery. Respiratory movements with amplitudes of 5 mm (R05) and 10 mm (R10) were simulated using a dynamic platform combined with a motorized jack. To evaluate dose errors caused by respiratory movement, the measured data in the presence and absence of respiratory movement were compared.Results At IM, dose errors were − 2.8% (R05) and − 6.2% (R10) for 3D-CRT and − 4.9% (R05) and − 8.5% (R10) for VMAT. The dose errors in CW were − 0.5% (R05) and − 6.0% (R10) for 3D-CRT and − 1.9% (R05) and − 5.3% (R10) for VMAT. The LAD doses showed very small absolute values. According to film measurements, dose errors of IMN were similar between 3D-CRT and VMAT, but the dose error of the lung was higher in 3D-CRT. The gamma pass rates of VMAT (97% at R05; 88% at R10) were higher than those of 3D-CRT (74% at R05; 59% at R10).Conclusions If the patient maintained shallow to normal breathing, PMRT including IMNs could be implemented with acceptable accuracy. In particular, it was possible to maintain the advantages of VMAT, which enabled high-target coverage and normal organ protection.