Analysis of the evaluation errors of dose-volume parameters for left ventricular myocardium in esophageal cancer radiotherapy

Objective: To evaluate the dynamic variation of the dose-volume parameters of the left ventricular myocardium following heart beat in radiotherapy for esophageal cancer. Methods: The left ventricular myocardium of 22 patients was contoured on 20 phases (0%-95%) of electrocardiography (ECG) gated heart 4DCT images. The radiotherapy plan was designed on the simulation CT images, and then the dose distribution of radiotherapy plan was imported into MIM Maestro system and 4D dose-volume histogram (DVH) was reconstructed. The variations of position, volume and dice similarity coefficient (DSC) of the left ventricular myocardium were analyzed. The changing ranges of D_mean, V₁₀, V₂₀, V₃₀ and V₄₀ of the left ventricular myocardium during different phases were statistically compared. Results: (1) The biggest displacement of the left ventricular myocardium was in Y axes. The maximum variation rate of volume and DSC of the left ventricular myocardium were (24.23 ± 11.35)% and (184.33 ± 128.61)% in different phases with statistical significance (both P < 0.05). (2) The maximum variation rate of D_mean of the left ventricular myocardium was (87.05 ± 38.34)% in different phases with the highest rate of 163.52% with statistical significance (P < 0.05). (3) The maximum variation values of V₁₀, V₂₀, V₃₀ and V₄₀ of the left ventricular myocardium were (13.64 ± 4.33)%, (12.84 ± 4.55)%, (11.62 ± 4.85)% and (3.63 ± 2.56)% with statistical significance (all P < 0.05). Conclusions: The impact of heart beat on the dose-volume parameters of the left ventricular myocardium should be considered during esophageal cancer radiotherapy. Traditional static 3DCT-based assessment of the dose-volume parameters of the left ventricular myocardium can yield relatively large errors, which is probably reduces the prediction efficiency of the dose-volume parameters for radiation-induced heart injury. (authors)