Comparison of initial computed tomography-based target delineation and subsequent magnetic resonance imaging-based target delineation for cervical cancer brachytherapy

Abstract

Purpose: For cervical brachytherapy planning, magnetic resonance imaging (MRI) is preferable to computed tomography (CT) for target delineation. However, due to logistical and financial restrictions, in-room MRI is sometimes not routinely available in brachytherapy centers. Our institution has created a workflow that integrates MRI-based target delineation with an in-room CT scanner, with the aim of improving target coverage and conformality. This study reports the initial dosimetric results with using this workflow. Material and methods: A retrospective review was performed on 46 consecutive patients who received definitive chemoradiation with 5 fraction intracavitary high-dose-rate (HDR) brachytherapy for cervical cancer. Fraction 1 was planned from CT only. Outpatient MRI was obtained after Smit sleeve placement and first insertion to assess concurrent chemoradiotherapy tumor response. This MRI was registered to the CT for planning fractions 2-5. The median prescription dose for the cohort was 25 Gy (range, 25-29 Gy). Results: The D 90 to the high-risk clinical target volume (HR-CTV) and D 2cc rectal dose were increased from fraction 1 to fraction 2-5 averaged (p < 0.05). Among the 18 patients with complete volumetric data, there was no significant difference in HR-CTV size, with an average decrease of 1.73 cc (p > 0.05) with MRI fusion. Eleven out of 18 patients had changes in high-risk target volume greater than 20%, with an absolute average change in volume of 31.5%. Conclusions: The use of asynchronous MRI for target delineation, with co-registration to CT for each fraction of brachytherapy was associated with higher D 90 to the HR-CTV. We observed slightly higher D 2cc rectal doses with MRI, but cumulative rectal doses were within accepted thresholds. High-risk target volumes were not consistently increased or decreased, but MRI fusion was associated with target volume changes greater than 20% in over half of the treated patients.

High-Dose-Rate Three-Dimensional Image-Guided Adaptive Brachytherapy (3D IGABT) for Locally Advanced Cervical Cancer (LACC): A Narrative Review on Imaging Modality and Clinical Evidence

“…This approach could incorporate MRI-based target definition while retaining the advantages of a CT-based workflow. Dose analysis [61] showed that MRI fusion allowed the dose distribution to be adjusted according to individual anatomical characteristics, thus reducing excessive or insufficient coverage. Another study conducted by Choong et al [55] obtained both MRI and CT with applicators in situ at F1, and subsequently registered these images in the follow-up fraction CT images, yielding promising results.…”

Characteristics of preplan‐based three‐dimensional individual template‐guided brachytherapy compared to freehand implantation

“…Nowadays, image-guided adaptive brachytherapy (IGABT) has gained considerable attention, as it can improve the therapeutic efficacy of tumor control without enhancing the obvious toxicity of organs at risk (OARs). [1][2][3][4][5] However, the local control rate in LACC can fall off for the unfavorable isodose of the high-risk clinical target volume (HR CTV) treated with ICBT only in the presence of characteristics such as large tumor volume, eccentric location, irregular shape, and parametrial or other site invasions. 6 Based on previous studies, imageguided adaptive intracavitary/interstitial brachytherapy (IC/IS IGABT) is superior in terms of dosimetry advantages and local control rate for the treatment of large tumors.…”

“…External beam radiotherapy (EBRT) combined with synchronous chemotherapy followed by intracavitary brachytherapy (ICBT) is the traditional standard strategy for locally advanced cervical cancer (LACC). Nowadays, image‐guided adaptive brachytherapy (IGABT) has gained considerable attention, as it can improve the therapeutic efficacy of tumor control without enhancing the obvious toxicity of organs at risk (OARs) 1–5 . However, the local control rate in LACC can fall off for the unfavorable isodose of the high‐risk clinical target volume (HR CTV) treated with ICBT only in the presence of characteristics such as large tumor volume, eccentric location, irregular shape, and parametrial or other site invasions 6 .…”