Postmastectomy radiotherapy for left-sided breast cancer patients: Comparison of advanced techniques

Abstract

Postmastectomy radiotherapy (PMRT) has been shown to improve the overall survival for invasive breast cancer patients, and many advanced radiotherapy technologies were adopted for PMRT. The purpose of our study is to compare various advanced PMRT techniques including fixed-beam intensity-modulated radiotherapy (IMRT), non-coplanar volumetric modulated arc therapy (NC-VMAT), multiple arc VMAT (MA-VMAT), and tomotherapy (TOMO). Results of standard VMAT and mixed beam therapy that were published by our group previously were also included in the plan comparisons. Treatment plans were produced for nine PMRT patients previously treated in our clinic. The plans were evaluated based on planning target volume (PTV) coverage, dose homogeneity index (DHI), conformity index (CI), dose to organs at risk (OARs), normal tissue complication probability (NTCP) of pneumonitis, lifetime attributable risk (LAR) of second cancers, and risk of coronary events (RCE). All techniques produced clinically acceptable PMRT plans. Overall, fixed-beam IMRT delivered the lowest mean dose to contralateral breast (1.56 ± 0.4 Gy) and exhibited lowest LAR (0.6 ± 0.2%) of secondary contralateral breast cancer; NC-VMAT delivered the lowest mean dose to lungs (7.5 ± 0.8 Gy), exhibited lowest LAR (5.4 ± 2.8%) of secondary lung cancer and lowest NTCP (2.1 ± 0.4%) of pneumonitis; mixed beam therapy delivered the lowest mean dose to heart (7.1 ± 1.3 Gy) and exhibited lowest RCE (8.6 ± 7.1%); TOMO plans provided the most optimal target coverage while delivering higher dose to OARs than other techniques. Both NC-VMAT and MA-VMAT exhibited lower values of all OARs evaluation metrics compare to standard VMAT. Fixed-beam IMRT, NC-VMAT, and mixed beam therapy could be the optimal radiation technique for certain breast cancer patients after mastectomy.

Keywords: Intensity-modulated radiotherapy; Postmastectomy radiotherapy; Tomotherapy; Volumetric modulated arc therapy.

Fig. 1

Three-dimensional display of (a) two non-coplanar partial arcs for NC-VMAT. Red plane represents gantry plane at 15° couch angle and the yellow plane represents gantry plane at 345° couch angle; (b) six partial arcs for MA-VMAT. The CW arcs display in yellow curvature and CCW arcs in red curvature.

Fig. 2

Axial view of isodose distribution for fixed-beam IMRT, MA-VMAT, NC-VMAT, TOMO, mixed-beam therapy and standard VMAT plans for a typical PMRT patient. The red color wash represents the PTV.

Fig. 3

DVHs for fixed-beam IMRT, MA-VMAT, NC-VMAT, TOMO, mixed-beam therapy and standard VMAT plans for a typical PMRT patient.