Implications for dosimetric changes when introducing MR-guided brachytherapy for small volume cervix cancer: a comparison of CT and MR-based treatments in a single centre

Abstract

To evaluate cervix brachytherapy dosimetry with the introduction of magnetic resonance (MR) based treatment planning and volumetric prescriptions and propose a method for plan evaluation in the transition period. The treatment records of 69 patients were reviewed retrospectively. Forty one patients were treated using computed tomography (CT)-based, Point A-based prescriptions and 28 patients were treated using magnetic resonance (MR)-based, volumetric prescriptions. Plans were assessed for dose to Point A and organs at risk (OAR) with additional high-risk clinical target volume (HR-CTV) dose assessment for MR-based brachytherapy plans. ICRU-38 point doses and GEC-ESTRO recommended volumetric doses (D2cc for OAR and D100, D98 and D90 for HR-CTV) were also considered. For patients with small HR-CTV sizes, introduction of MR-based volumetric brachytherapy produced a change in dose delivered to Point A and OAR. Point A doses fell by 4.8 Gy (p = 0.0002) and ICRU and D2cc doses for OAR also reduced (p < 0.01). Mean Point A doses for MR-based brachytherapy treatment plans were closer to those of HR-CTV D100 for volumes less than 20 cm(3) and HR-CTV D98 for volumes between 20 and 35 cm(3), with a significant difference (p < 0.0001) between Point A and HR-CTV D90 doses in these ranges. In order to maintain brachytherapy dose consistency across varying HR-CTV sizes there must be a relationship between the volume of the HR-CTV and the prescription dose. Rather than adopting a 'one size fits all' approach during the transition to volume-based prescriptions, this audit has shown that separating prescription volumes into HR-CTV size categories of less than 20 cm(3), between 20 and 35 cm(3), and more than 35 cm(3) the HR-CTV can provide dose uniformity across all volumes and can be directly linked to traditional Point A prescriptions.

Contrast-enhanced ultrasonography vs MRI for evaluation of local invasion by cervical cancer

“…35 On the other hand, MRI is recommended as the best modality for image-guided brachytherapy due to its high image resolution and clear target volume definition. 36 Our present findings demonstrate good concordance of CEUS with MRI for evaluating tumour size and local invasion of cervical cancer. Thus, CEUS could be performed before brachytherapy to accurately determine the clinic stage, and it has the potential to be an alternative in brachytherapy of cervical cancer.…”

Role of MRI in staging of carcinoma cervix in correlation with USG and CT scan

“…Dempsey C, et al . [20] also recommended MRI is as the best modality for image-guided brachytherapy due to its high image resolution and clear target volume definition.…”