title: Design and testing of a phantom and instrumented gynecological applicator based on GaN dosimeter for use in high dose rate brachytherapy quality assurance.
abstract: OBJECTIVE
  High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (>5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively.
  
  
  METHODS
  The authors have designed a HDR-BT phantom equipped with four GaN-based dosimeters. The authors have also instrumented a commercial multichannel HDR-BT gynecological applicator by rigid incorporation of four GaN-based dosimeters in four channels. Specific methods based on the four GaN dosimeter responses are proposed for accurate determination of dwell time and dwell position inside phantom or applicator. The phantom and the applicator have been tested for HDR-BT QA in routine over two different periods: 29 and 15 days, respectively. Measurements in dwell position and time are compared to the treatment plan. A modified position-time gamma index is used to monitor the quality of treatment delivery.
  
  
  RESULTS
  The HDR-BT phantom and the instrumented applicator have been used to determine more than 900 dwell positions over the different testing periods. The errors between the planned and measured dwell positions are 0.11 ± 0.70 mm (1σ) and 0.01 ± 0.42 mm (1σ), with the phantom and the applicator, respectively. The dwell time errors for these positions do not exhibit significant bias, with a standard deviation of less than 100 ms for both systems. The modified position-time gamma index sets a threshold, determining whether the treatment run passes or fails. The error detectability of their systems has been evaluated through tests on intentionally introduced error protocols. With a detection threshold of 0.7 mm, the error detection rate on dwell position is 22% at 0.5 mm, 96% at 1 mm, and 100% at and beyond 1.5 mm. On dwell time with a dwell time threshold of 0.1 s, it is 90% at 0.2 s and 100% at and beyond 0.3 s.
  
  
  CONCLUSIONS
  The proposed HDR-BT phantom and instrumented applicator have been tested and their main characteristics have been evaluated. These systems perform unsupervised measurements and analysis without prior treatment plan information. They allow independent verification of dwell position and time with accuracy of measurements comparable with other similar systems reported in the literature.
authors: Service de Physique Médicale et Radioprotection, Centre Hospitalier Lyon Sud, Pierre-Bénite F-69495, France.
authors: P
authors: P
authors: Guiral
authors: Service de Physique Médicale et Radioprotection, Centre Hospitalier Lyon Sud, Pierre-Bénite F-69495, France.
authors: J
authors: J
authors: Ribouton
authors: Service de Physique Médicale et Radioprotection, Centre Hospitalier Lyon Sud, Pierre-Bénite F-69495, France.
authors: P
authors: P
authors: Jalade
authors: Institut des Nanotechnologies de Lyon, University Lyon, Université Claude Bernard Lyon 1, CNRS, INL UMR5270, F-69622 Villeurbanne, France.
authors: R
authors: R
authors: Wang
authors: Institut des Nanotechnologies de Lyon, University Lyon, Université Claude Bernard Lyon 1, CNRS, INL UMR5270, F-69622 Villeurbanne, France.
authors: J-M
authors: JM
authors: Galvan
authors: Institut des Nanotechnologies de Lyon, University Lyon, Université Claude Bernard Lyon 1, CNRS, INL UMR5270, F-69622 Villeurbanne, France.
authors: G-N
authors: GN
authors: Lu
authors: Institut des Nanotechnologies de Lyon, University Lyon, Université Claude Bernard Lyon 1, CNRS, INL UMR5270, F-69622 Villeurbanne, France.
authors: P
authors: P
authors: Pittet
authors: DOSILAB, 66 Boulevard Niels Bohr, Villeurbanne F-69100, France.
authors: A
authors: A
authors: Rivoire
authors: DOSILAB, 66 Boulevard Niels Bohr, Villeurbanne F-69100, France.
authors: L
authors: L
authors: Gindraux
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000592:standards; D004867:Equipment Design; D005260:Female; D005708:Gallium; D006176:Gynecology / Q000295:instrumentation*; D006801:Humans; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D013997:Time Factors; D035501:Uncertainty
chemical_list: C473348:gallium nitride; D005708:Gallium