title: A practical MRI-based reconstruction method for a new endocavitary and interstitial gynaecological template.
abstract: OBJECTIVE
  There 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.
  
  
  METHODS
  The 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Jose
authors.initials: J
authors.lastname: Richart
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Antonio
authors.initials: A
authors.lastname: Otal
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Silvia
authors.initials: S
authors.lastname: Rodriguez
authors.affiliation: Radiology Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Ana Isabel
authors.initials: AI
authors.lastname: Nicolás
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Marina
authors.initials: M
authors.lastname: DePiaggio
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante.
authors.forename: Manuel
authors.initials: M
authors.lastname: Santos
authors.affiliation: Atomic, Molecular and Nuclear Physics Department, University of Valencia, Burjassot, Valencia ; IFIC (CSIC-UV), Burjassot, Valencia.
authors.forename: Javier
authors.initials: J
authors.lastname: Vijande
authors.affiliation: Atomic, Molecular and Nuclear Physics Department, University of Valencia, Burjassot, Valencia.
authors.forename: Facundo
authors.initials: F
authors.lastname: Ballester
authors.affiliation: Radiotherapy Department, Benidorm Hospital, Benidorm, Alicante ; Radiotherapy Department, La Fe University and Polytechnic Hospital, Valencia, Spain.
authors.forename: Jose
authors.initials: J
authors.lastname: Perez-Calatayud
keywords: brachytherapy template; catheter reconstruction; gynecological template; interstitial implants