Improve definition of titanium tandems in MR-guided high dose rate brachytherapy for cervical cancer using proton density weighted MRI

Yanle Hu,Perry W Grigsby,Sasa Mutic,Susan Richardson,Julie K Schwarz,Hiram A Gay,Jacqueline Esthappan

doi:10.1186/1748-717x-8-16

Yanle Hu, Perry W Grigsby + Show 5 more

Open Access

https://doi.org/10.1186/1748-717x-8-16

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Abstract

BackgroundFor cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid. Standard T2-weighted (T2W) MRI has good tumor-tissue contrast. However, it suffers from poor uterus-tandem contrast, which makes the tandem delineation very challenging. In this study, we evaluated the possibility of using proton density weighted (PDW) MRI to improve the definition of titanium tandems.MethodsBoth T2W and PDW MRI images were obtained from each cervical cancer patient. Imaging parameters were kept the same between the T2W and PDW sequences for each patient except the echo time (90 ms for T2W and 5.5 ms for PDW) and the slice thickness (0.5 cm for T2W and 0.25 cm for PDW). Uterus-tandem contrast was calculated by the equation C = (Su-St)/Su, where Su and St represented the average signal in the uterus and the tandem, respectively. The diameter of the tandem was measured 1.5 cm away from the tip of the tandem. The tandem was segmented by the histogram thresholding technique.ResultsPDW MRI could significantly improve the uterus-tandem contrast compared to T2W MRI (0.42±0.24 for T2W MRI, 0.77±0.14 for PDW MRI, p=0.0002). The average difference between the measured and physical diameters of the tandem was reduced from 0.20±0.15 cm by using T2W MRI to 0.10±0.11 cm by using PDW MRI (p=0.0003). The tandem segmented from the PDW image looked more uniform and complete compared to that from the T2W image.ConclusionsCompared to the standard T2W MRI, PDW MRI has better uterus-tandem contrast. The information provided by PDW MRI is complementary to those provided by T2W MRI. Therefore, we recommend adding PDW MRI to the simulation protocol to assist tandem delineation process for cervical cancer patients.

Highlights

For cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid
To show the effectiveness of using proton density weighted (PDW) magnetic resonance imaging (MRI) in assisting the delineation of the “tandem and ovoid” applicator, we retrospectively reviewed MRI images from cervical cancer patients who were treated with MR-guided high dose rate (HDR) brachytherapy in our clinic and had both T2W and PDW images acquired
The average uterus-tandem contrast from all patients was 0.42±0.24 for T2W MRI and 0.77±0.14 for PDW MRI

Summary

Introduction

For cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid. Standard T2-weighted (T2W) MRI has good tumor-tissue contrast. It suffers from poor uterus-tandem contrast, which makes the tandem delineation very challenging. CT is considered as the standard imaging modality for radiotherapy treatment planning for cervical cancer. It is fast and has a good spatial resolution. MRI does not involve any ionizing radiation and won’t add radiation dose to patients Those advantages make MRI highly desirable in radiation oncology, especially in pelvic area such as cervical cancer

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