SU-E-T-593: Evaluation of Titanium Applicator Reconstruction Accuracy for Exclusive 3.0 Tesla MRI-Guided Brachytherapy for GYN Cancers

Abstract

Purpose: To evaluate applicator reconstruction accuracy using titanium tandem‐and‐ovoids applicator (TnO) when guided exclusively by high resolution (3 Tesla) MRI. Methods: MRI‐marker catheters (Vitamin‐E) are made in‐house. A titanium Fletcher‐Suit‐Delclos‐style TnO (Varian) was used. Nineteen HDR plans were randomly selected and TnO was reconstructed exclusively on MRI using the guidance from an applicator library (Solid Applicator, Varian) and a MRI‐marker. For control, TnO reconstructions were retrospectively performed on two radiographs before and after the MR scan (pre‐ and post‐Xray). The vector distances (d) were measured between each dwell position and a flenge. The differences of d (delta‐d) on the reconstructions between of MRI and of pre‐Xray (preXray‐ MRI) and between of MRI and post‐Xray (MRI‐postXray) were measured. The delta‐d values were used to quantify the reconstruction uncertainty on exclusive MrIGBT. The average (± std dev) of delta‐d for each dwell position was determined for each TnO plan. Results: We found on average delta‐d = 0.8 ± 0.5 mm (1.0 ± 0.5 mm) for preXray‐MRI (MRI‐postXray). The values of delta‐d were on average 0.9 ±0.1 mm and 0.8 ± 0.3 mm (1.0 ± 0.2 mm and 0.9 ± 0.4 mm) at tandem and ovoids for MRI‐preXray (MRI‐ postXray). The ovoid shape available for use from the applicator library was found to be beneficial, since the MRI‐marker could not generate signals for the ovoids. However, two cases showed delta‐d = more than 2 mm. The largest delta‐d values were on average 3.7 ± 0.3 mm (3.2 ± 0.8 mm) at tandem for preXray‐MRI (MRI‐postXray). Therefore, further studies on better MRI‐marker designs are expected to be followed for exclusive MrIGBT. Conclusions: The reconstruction uncertainties for exclusive MrIGBT using titanium applicators were on average less than 1.0 mm but exceeded 3.7 mm in one case. The first author, Yusung Kim, has been performed a research with the collaboration grant from Varian (Medical System; $124,160.42 Jan 2011 – July 2012).