A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template

Abstract

PurposeThere are perineal templates for interstitial implants such as MUPIT and Syed applicators. Their limitations are the intracavitary component deficit and the necessity to use computed tomography (CT) for treatment planning since both applicators are non-magnetic resonance imaging (MRI) compatibles. To overcome these problems, a new template named Template Benidorm (TB) has been recently developed. Titanium needles are usually reconstructed based on their own artifacts, mainly in T1-weighted sequence, using the void on the tip as the needle tip position. Nevertheless, patient tissues surrounding the needles present heterogeneities that complicate the accurate identification of these artifact patterns. The purpose of this work is to improve the titanium needle reconstruction uncertainty for the TB case using a simple method based on the free needle lengths and typical MRI pellets markers.Material and methodsThe proposed procedure consists on the inclusion of three small A-vitamin pellets (hyperintense on MRI images) compressed by both applicator plates defining the central plane of the plate's arrangement. The needles used are typically 20 cm in length. For each needle, two points are selected defining the straight line. From such line and the plane equations, the intersection can be obtained, and using the free length (knowing the offset distance), the coordinates of the needle tip can be obtained. The method is applied in both T1W and T2W acquisition sequences. To evaluate the inter-observer variation of the method, three implants of T1W and another three of T2W have been reconstructed by two different medical physicists with experience on these reconstructions.Results and conclusionsThe differences observed in the positioning were significantly smaller than 1 mm in all cases. The presented algorithm also allows the use of only T2W sequence either for contouring or reconstruction purposes. The proposed method is robust and independent of the visibility of the artifact at the tip of the needle.

Pre-plan technique feasibility in multi-interstitial/endocavitary perineal gynecological brachytherapy

“…The design allows covering any desired volume in gynecological cancer from distal vagina to uterus and distal parametrium, avoiding possible errors of free-hand needle placement. This device is constructed using a template, which is fixed to the perineum, allowing the employment of titanium needles and an intrauterine component to provide a central brachytherapy dose [ 9 , 10 , 11 ]. The template consists in two perineal plates with two central holes, allowing placement of a vaginal cylinder (available in different sizes) to accommodate different vaginal lengths.…”

“…Magnetic resonance imaging acquisition setting details were included in a previous publication from Richart et al . [ 11 ].…”

Development and clinical implementation of a new template for MRI-based intracavitary/interstitial gynecologic brachytherapy for locally advanced cervical cancer: from CT-based MUPIT to the MRI compatible Template Benidorm. Ten years of experience

“…Pre-implant imaging with CT (LightSpeed VCT, GE Medical Systems, Milwaukee, Wisconsin, USA) for MUPIT patients, or MRI (Optima MR450w, GE Medical Systems, Milwaukee, Wisconsin, USA) for TB patients was completed with the respective templates and a vaginal obturator of a known length (13 cm for MUPIT and 4-12 cm for TB according to the vaginal length) in place, and the bladder filled with 50 cm 3 of saline solution. Contiguous 2.5 mm thick CT slices and T2 weighted axial MRI images were taken (Figure 2A-F) [12]. The number, position, and depths of the needles were defined using these images, always allowing an offset of 10 mm from the tip of the needle to describe the first dwell position.…”

“…In order to improve perineal interstitial brachytherapy by incorporating MRI into these treatments, we developed Template Benidorm (TB) [11, 12] (Lorca Marín S.A, Murcia, Spain). This applicator is completely compatible with MRI and allows for combination of intracavitary radiotherapy and MRI-compatible transperineal interstitial needles (IS).…”

Review of strategies for MRI based reconstruction of endocavitary and interstitial applicators in brachytherapy of cervical cancer

“…A second template, carved with three dimples on it, is attached to the first one to insert three markers that simplify the reconstruction process. 34 Another institution-specific template, the Pamplona applicator, based on the geometry of the MUPIT applicator from Elekta (Elekta, Veenendaal, The Netherlands), was modified to be used in MR, see Fig. 1c.…”