Dosimetric Comparison of SEQ versus SIB-VMAT in the Treatment of Esophageal Cancer
Keywords:
Esophageal Cancer, VMAT, Simultaneous Integrated Boost (SIB), Sequential Boost (SEQ), Conformity Index, Homogeneity Index, Organs at Risk, Dosimetric Comparison, Radiotherapy.Abstract
Background: Esophageal cancer carries a high global mortality burden. Two dose-escalation techniques are available with VMAT-based radiation therapy: sequential boost (SEQ) and simultaneous integrated boost (SIB). However, there is little direct dosimetric comparison of these methods in esophageal cancer.
Objective: This study aimed to compare SEQ-VMAT and SIB-VMAT in locally advanced esophageal cancer using OAR dosage parameters, conformity index (CI), and homogeneity index (HI).
Methods: Ten patients with histopathologically proven locally advanced esophageal cancer were included in this retrospective dosimetric study: SEQ-VMAT (n=5) and SIB-VMAT (n=5). SEQ delivered 45 Gy/25 fx, followed by a boost to 50.4 Gy/28 fx; SIB delivered 50.4 Gy (1.8 Gy/fr) to GTV and 45 Gy (1.61 Gy/fx) to PTV concurrently in 28 fractions. DVH-based dosimetric parameters (CI, HI, V95%, OAR doses) were analyzed against QUANTEC tolerances. Statistical analysis was performed using SPSS v25.0 (p<0.05).
Results: Both techniques achieved adequate PTV coverage (median V95% 96.1% vs. 95.5%). SIB-VMAT showed significantly better conformity (CI 0.90 vs. 0.76, p=0.012) and significantly lower left lung mean dose and V20 (both p<0.02), whereas SEQ-VMAT showed significantly better homogeneity (HI 0.08 vs. 0.15, p=0.021). All other OAR doses were statistically equivalent between the groups and within the QUANTEC tolerances.
Conclusion: Both SEQ-VMAT and SIB-VMAT achieved adequate target coverage and kept organ-at-risk doses within QUANTEC-based tolerances for locally advanced esophageal cancer. SIB-VMAT showed significantly better conformity and lower left lung dose, whereas SEQ-VMAT showed significantly better dose homogeneity; other organ-at-risk parameters were statistically equivalent between the two techniques. Given this trade-off, its shorter overall treatment course, and the small sample size studied, SIB-VMAT may be considered a practical alternative to SEQ-VMAT, though larger studies are needed before either technique can be recommended as preferred.
