Dose comparison between variable angle and semi-orthogonal reconstruction techniques of the Fletcher applicator in 2D-based brachytherapy

Abstract

Background: The applicator reconstruction uncertainties lead to an incorrect dose distribution for the patient. Objective: To compare the point dose between the variable angle (VA) reconstruction technique and the semi-orthogonal (SO) reconstruction technique of the Fletcher applicator in 2D-based brachytherapy treatment planning. Materials and methods: The applicators, tandem and tandem + ovoid set, in water equivalent in-house phantom with a localization jig were exposed at 0o and 90o gantry angles by conventional treatment simulator (Varian Acuity). The applicators were set at the localization jig center and the machine isocenter, 4 cm shifted in right, left, cranial and caudal directions. These 5 image sets were exported to brachytherapy treatment planning system, Oncentra Brachy v.4.3. Both VA and SO used the same images. The dwell positions and dwell times were identical defined for both techniques. The dose at 4 reference points at right, left, anterior, and posterior around the applicator were compared each technique. Results: When the applicator was not at the center of the device, the maximum dose difference shown at cranial-caudal shifted in tandem + ovoid was 6.48 ± 1.78% (4.01 to 8.97%) while the applicator set at the center of the device, the maximum dose difference shown in tandem + ovoid was 1.72 ± 1.25% (0.21 to 2.76%). The details of the study were in the article. Conclusion: Based on this study, the two techniques could be used interchangeably although the applicator was 4 cm shifted of the applicator in right, left directions from the center of the localization jig but should not shift to cranial and caudal direction. The maximum dose difference was found in the tandem + ovoid set.