Comparative dosimetric evaluation of hybrid volumetric modulated arc therapy techniques for oesophageal cancer: a treatment planning study

Abstract Objective: To find the optimal dose weighting for a combination of three-dimensional conformal radiotherapy (3DCRT) and hybrid volumetric modulated arc therapy (hVMAT) plans for thoracic oesophageal cancer radiation therapy. Methods and Materials: This retrospective study involved fourteen patients diagnosed with carcinoma of the oesophagus previously treated with VMAT radiotherapy techniques. Four hVMAT plans were developed for each patient, with a prescribed dose of 50.4 Gy delivered over 28 fractions. The plans incorporated varying ratios of 3DCRT and VMAT techniques: hVMAT-1(33% 2F 3DCRT/67% VMAT), hVMAT-2 (33% 3F 3DCRT/67% VMAT), hVMAT-3 (67% 2F 3DCRT/33% VMAT), and hVMAT-4 (67% 3F 3DCRT/33% VMAT). Dose volume histograms were used to assess the coverage of the planning target volume (PTV) and to analyse dosimetric parameters, including the doses received by organs at risk. Result: In the four hVMAT techniques, statistically insignificant differences were observed in PTV doses, conformity index and homogeneity index. Notably, monitor unit values differed significantly in three techniques, except for hVMAT-1(p = 0.358). hVMAT-3 demonstrated lower lung mean dose and lung V 20Gy values (14.5±3.97, 21.09 ± 9.02) compared to other techniques. There were statistically significant differences in heart mean doses between hVMAT-1 and hVMAT-2, or hVMAT-3 and hVMAT-4 plans (p = 0.462, p = 0.542). However, a significant difference in spinal cord Dmax was found only in hVMAT-1(p = 0.024). Conclusion: The hVMAT -1 and hVMAT-2 techniques (33% 2F 3DCRT/67% Arc) appear to be the most suitable weighting for the hybrid VMAT technique, offering optimal sparing of the lungs and heart while ensuring adequate coverage of the planning target volume.