Evaluating the performance of TG-43 protocol in esophageal HDR brachytherapy viewpoint to trachea inhomogeneity

Abstract

Aim

The aim of this study is to evaluate the effect of air within trachea on dose calculations of esophageal HDR brachytherapy treatment planning.

Background

Dose calculations in esophageal HDR brachytherapy treatment planning systems are greatly based on TG-43 protocol which in all materials are considered to be water equivalent.

Materials and methods

A cylindrical PMMA phantom with a tube in the center (neck equivalent phantom) accompanied by Flexitron HDR brachytherapy system was used in this study. Brachytherapy applicators with various diameters were placed inside the esophageal tube and EDR2 film was used for dosimetry. The absorbed dose by reference point of esophageal HDR brachytherapy and anterior wall of trachea were measured and compared with those calculated by Flexiplan treatment planning system.

Results

Based on the performed statistical analysis (t-test) with 95% confidence level (t-value >1.96), there was a meaningful difference between the results of film dosimetry and treatment planning at all of the points understudy.

Conclusion

The meaningful difference between the results of film dosimetry and treatment planning indicates that the trachea inhomogeneity has a considerable effect on dose calculations of Flexiplan treatment planning software featuring the TG-43 dose calculation algorithm. This mismatch can affect the accuracy of performed treatment plan and irradiation.