First pointwise encoding time reduction with radial acquisition (PETRA) implementation for catheter detection in interstitial high-dose-rate (HDR) brachytherapy



      A pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized to detect empty catheters in interstitial (HDR) brachytherapy with clinically acceptable spatial accuracy for the first time. Image quality and catheter detectability were assessed in phantoms, and the feasibility of PETRA's clinical implementation was assessed on a gynecological cancer patient.


      Empty catheters embedded in a gelatin phantom displayed positive signal on PETRA and more accurate cross-sections than on clinically employed T2-weighted sequences, differing by 0.4 mm on average from their nominal 2 mm diameter. PETRA presented minimal susceptibility differences and a symmetric metal artifact, contrary to the clinical sequences. The PETRA-CT catheter tip position differences assessed by a treatment planning system (TPS) were < 1 mm. PETRA also detected an interstitial template with empty catheters penetrating a poultry phantom and fused very well with CT. Interstitial catheter positional difference between PETRA and CT images was < 1 mm on average, increasing with distance from isocenter. All interstitial catheters and the employed interstitial template were detected on PETRA images of an endometrial adenocarcinoma patient. Empty needles were traceable using a TPS, with higher spatial resolution and more favorable contrast than on T2-weighted images used for contouring. A treatment plan could be produced by combining information from PETRA for catheter detection and from T2-weighted images for tumor and organs delineation.


      PETRA detected successfully and accurately interstitial catheters in phantoms. Its first clinical implementation shows a potential for MR-only treatment planning in interstitial HDR brachytherapy.


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        • Dimopoulos J.C.A.
        • Petrow P.
        • Tanderup K.
        • et al.
        Recommendations from Gynecological (GYN) GEC-ESTRO Working Group (4): basic principles and parameters for MR imaging within the frame of image based adaptive cervix cancer brachytherapy.
        Radiother Oncol J Eur Soc Ther Radiol Oncol. 2012; 103: 113-122
        • Sander T.
        Air kerma and absorbed dose standards for reference dosimetry in brachytherapy.
        Br J Radiol. 2014; 87: 10
        • Richart J.
        • Carmona-Meseguer V.
        • García-Martínez T.
        • et al.
        Review of strategies for MRI based reconstruction of endocavitary and interstitial applicators in brachytherapy of cervical cancer.
        Reports Pract Oncol Radiother [Internet]. 2018; 23: 547-561
        • Glide-Hurst C.K.
        • Paulson E.S.
        • McGee K.
        • et al.
        Task group 284 report: magnetic resonance imaging simulation in radiotherapy: considerations for clinical implementation, optimization, and quality assurance.
        Med Phys. 2021; 48: e652-e657
        • Nath R.
        • Anderson L.L.
        • Meli J.A.
        • et al.
        Code of practice for brachytherapy physics: report of the AAPM radiation therapy committee task group no. 56.
        Med Phys. 1997; 24: 1557-1598
        • Nosrati R.
        • Paudel M.
        • Ravi A.
        • et al.
        Potential applications of the quantitative susceptibility mapping (QSM) in MR-guided radiation therapy.
        Phys Med Biol [Internet]. 2019; 64: ab2623
        • Ning M.S.
        • Vedam S.
        • Ma J.
        • et al.
        Clinical utility and value contribution of an MRI-positive line marker for image-guided brachytherapy in gynecologic malignancies.
        Brachytherapy. 2020; 19: 305-315
        • Springer F.
        • Martirosian P.
        • Schwenzer N.F.
        • et al.
        Three-dimensional ultrashort echo time imaging of solid polymers on a 3-tesla whole-body MRI scanner.
        Invest Radiol. 2008; 43: 802-808
        • Robson M.D.
        • Bydder G.M.
        Clinical ultrashort echo time imaging of bone and other connective tissues.
        NMR Biomed. 2006; 19: 765-780
        • van den Ende R.P.J.
        • Ercan E.
        • Keesman R.
        • et al.
        Applicator visualization using ultrashort echo time MRI for high-dose-rate endorectal brachytherapy.
        Brachytherapy [Internet]. 2020; 19: 618-623
        • Weiger M.
        • Pruessmann K.P.
        • Hennel F.
        MRI with zero echo time: hard versus sweep pulse excitation.
        Magn Reson Med. 2011; 66: 379-389
        • Grodzki D.M.
        • Jakob P.M.
        • Heismann B.
        Ultrashort echo time imaging using pointwise encoding time reduction with radial acquisition (PETRA).
        Magn Reson Med. 2012; 67: 510-518
        • Lee Y.H.
        • Suh J.S.
        • Grodzki D.
        Ultrashort echo (UTE) versus pointwise encoding time reduction with radial acquisition (PETRA) sequences at 3 Tesla for knee meniscus: a comparative study.
        Magn Reson Imaging. 2016; 34: 75-80
        • Ladd M.E.
        • Erhart P.
        • Debatin J.F.
        • et al.
        Biopsy Needle Susceptibility Artifacts in Magnetic Resonance Imaging.
        Magn Reson Med. 1996; 36: 646-651
        • Kaza E.
        • Cormack R.
        • Devlin P.
        • Buzurovic I.
        MRI visualization of applicators for skin HDR brachytherapy.
        in: AAPM virtual conference. 2020 ([Internet]Available at:)
        • Kirisits C.
        • Rivard M.J.
        • Baltas D.
        • et al.
        Review of clinical brachytherapy uncertainties: analysis guidelines of GEC-ESTRO and the AAPM.
        Radiother Oncol. 2014; 110: 199-212
        • Lee C.Y.
        • Kaza E.
        • Devlin P.M.
        • Cormack R.A.
        Buzurovic I. Feasibility of MR-only high-dose-rate (HDR) surface brachytherapy for clinical application.
        Med Phys. 2021; 48: 7313-7322