Improvement of helical tomotherapy treatment plan efficiency with block techniques for left-sided post-mastectomy radiation therapy

Purpose: To limit the entrance dose to normal tissue and achieve the appropriate treatment time (TT) by using three different virtual structures with directional blocks for left-sided post-mastectomy radiation therapy (PMRT) with regional nodal irradiation (RNI). Methods and materials: Ten breast cancer patients who received PMRT by helical tomotherapy were enrolled. Three virtual structures were created for each patient: Organ-based, L-shaped (LB) and C-shaped (CB). The dose to the target and organ at risk (OARs), TT, the volume which received dose 5 Gy (V5Gy), integral dose (ID) and block structure contouring workload (BSCW) of the three virtual block techniques were evaluated. The performance scores were used to explore the suitable technique. Results: The CB plans showed a significantly better V5Gy, ID and contralateral breast-sparing. However, the CB plans revealed the longest TT and BSCW (p < 0·001). Contrary to the LB, the LB plans showed a significantly reduced TT and BSCW and provided the balance of plan efficiency with the highest score. Conclusion: The LB technique is considered to be the suitable technique for left-sided PMRT with RNI and provided the advantage of TT, V5Gy, ID and BSCW while maintaining acceptable criteria for the target and OARs.