การปรับปรุงประสิทธิภาพแผนรังสีตัดขวางแบบเกลียวหมุนโดยใช้เทคนิคการจำกัดทิศทางลำรังสีสำหรับการฉายรังสีผู้ป่วยมะเร็งเต้านมหลังผ่าตัดด้านซ้าย

Abstract

Introduction: Helical Tomotherapy (HT) is the recent treatment technique for post-mastectomy radiation therapy (PMRT) with regional nodal irradiation (RNI). HT can deliver highly conformal dose distribution to the tumor while avoiding the high dose to the organ at risk (OARs). However, HT increases in the low-dose region due to the 360-degree treatment delivery. Therefore, using the block structure to limit the beam direction is the alternative technique for helical tomotherapy treatment planning. Purpose: To improve helical tomotherapy plan efficiency by using virtual structures with block techniques, and compare the efficacy to reduce the radiation dose to OARs, low dose volume and treatment time for determining the suitable planning technique for left-sided PMRT with RNI. Method: Ten left-sided PMRT with the chest wall and regional nodal irradiation who treated by HT. Six virtual block structures were created as organ-based virtual block with a margin of 2 cm and 3 cm from PTV (OB2cm and OB3cm respectively), L-shaped virtual block inside and outside body contour (LB In and LB Out respectively), and C-shaped virtual block with a margin of 9 cm and 10 cm from PTV (CB9cm and CB10cm respectively). Furthermore, all six techniques were compared with the reference plans including Unblocked and Organ-based directional block (OBDB). The target coverage, homogeneity index, conformation number, OARs dose, whole-body volume received dose 5 Gy (V5Gy), integral dose, treatment time, and block structure contouring workload of the six virtual block techniques were assessed. The plan quality scores were used to investigate the suitable technique. Result: Overall dosimetric comparison, the CB9cm plans can reduce the low dose to the contralateral breast but significantly increased in treatment time and block structure contouring workload with the highest plan quality score. However, the LB Out plans can achieve acceptable criteria and significantly reduced treatment time and block structure contouring workload when compared with other plans. Furthermore, the LB Out technique showed the highest plan quality score when considering in plan efficiency parameters. Conclusion: The LB Out is the suitable technique for helical tomotherapy treatment planning for Left-sided PMRT with RNI because LB out decreases the low dose volume and reduces the treatment time while achieving acceptable criteria for OARs.