title: D2cm³/DICRU ratio as a surrogate of bladder hotspots localizations during image-guided adaptive brachytherapy for cervical cancer: assessment and implications in late urinary morbidity analysis.
abstract: OBJECTIVE
  To evaluate the efficiency and potential implications of the lowest dose evaluated in the maximally exposed 2cm(3) of the bladder/dose evaluated at the International Commission for Radiation Units and Measurements (ICRU) bladder point (D2cm(3)/DICRU) ratio as surrogate to locate the D2cm(3) in patients treated with MRI-guided adaptive brachytherapy for cervical cancer.
  
  
  METHODS
  The D2cm(3) area of the bladder was located in 69 patients, using the Digital Imaging and Communications in Medicine coordinates of its barycenter, with respect to the ICRU bladder point. The D2cm(3)/DICRU ratio was correlated with the longitudinal coordinate of the D2cm(3). Afterward, the ratio was used in a retrospective cohort of 216 patients to evaluate its impact in dose-effect analyses for late urinary incontinence.
  
  
  RESULTS
  The mean position of the D2cm(3) was 1.73±0.98 cm cranially, 0.59±0.65 cm backwardly, and 0.02±0.89 cm to the right of the ICRU point. It was located above the ICRU point in 95.7% of the patients. Its position was lower in patients with vaginal involvement at diagnosis (p=0.03). The D2cm(3)/DICRU ratio was correlated with the position of the D2cm(3) (R²=0.716, p<10(-6)). In speculating that a ratio greater than one would predict a D2cm(3) located above the ICRU point, the sensibility, specificity, positive, and negative predictive values were 95.2%, 100%, 100%, and 66.8%, respectively. Among the retrospective cohort, 85 patients had a ratio lower than 1.1, reflecting a D2cm(3) located in the lower bladder. In these patients, analyses showed significant dose relationship with Grade 2-4 incontinence (p=0.017), whereas no correlation was demonstrated in the remaining patients.
  
  
  CONCLUSIONS
  The D2cm(3)/DICRU ratio is a relevant surrogate to estimate the localization of the D2cm(3). Significant dose-effect correlations for incontinence were established in patients with low values for this ratio.
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France; Department of Molecular Radiotherapy-UMR1030, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France. Electronic address: renaud.mazeron@gustaveroussy.fr.
authors.forename: Renaud
authors.initials: R
authors.lastname: Mazeron
authors.affiliation: Department of Medical Physics, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Dumas
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Eleonor
authors.initials: E
authors.lastname: Rivin
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Valentine
authors.initials: V
authors.lastname: Martin
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Wassila
authors.initials: W
authors.lastname: Benhabib-Boukhelif
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Tailleur
authors.affiliation: Department of Medical Physics, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Guemnie-Tafo
authors.affiliation: Department of Medical Physics, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Martinetti
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Cyrus
authors.initials: C
authors.lastname: Chargari
authors.affiliation: Department of Molecular Radiotherapy-UMR1030, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France; Department of Medical Physics, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Lefkopoulos
authors.affiliation: Department of Radiation Therapy, Gustave Roussy Cancer Campus Grand Paris, Villejuif, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Haie-Meder
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000379:methods*; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009017:Morbidity / Q000639:trends; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012189:Retrospective Studies; D018570:Risk Assessment; D001743:Urinary Bladder / Q000528:radiation effects*; D001745:Urinary Bladder Diseases / Q000453:epidemiology* / Q000209:etiology; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
keywords: Bladder; Cervical cancer; D2cm(3); ICRU point; Image-guided adaptive brachytherapy; Urinary incontinence