title: Superior target volume and organ stability with the use of endorectal balloons in post-prostatectomy radiotherapy.
abstract: BACKGROUND
  We investigated the endorectal balloon (ERB) as a method to improve post-prostatectomy clinical target volume (CTV) stability.
  
  
  METHODS
  Seventy cone-beam CT (CBCT) obtained during radiotherapy treatment from seven patients treated with an ERB and 68 CBCT from seven patients treated without an ERB were contoured according to published guidelines. CTV was subdivided into superior and inferior CTV; whole rectal volume was subdivided into superior and inferior rectum and anal volume. Concordance index (CI) of CBCT treatment volumes compared with planning volumes was calculated and displacements were measured.
  
  
  RESULTS
  Whole rectal, superior and inferior rectum and anal CI were significantly improved with the ERB by 21%, 17%, 26% and 17% respectively (P < 0.0001). Overall CTV and inferior CTV CI was improved by 4% with the ERB (overall CTV P = 0.021; Inferior CTV P < 0.0001). In the ERB cohort, average displacement for superior CTV was 0.37 cm anterior-posterior (AP) and 0.10 cm left-right (LR). Average standard deviation was 0.27 cm AP and 0.11 cm LR. Inferior CTV average displacement was 0.11 cm AP and 0.02 cm LR. Average standard deviation was 0.11 cm AP and 0.02 cm LR. In the non-ERB cohort, average displacement for superior CTV was 0.43 cm AP and 0.10 mm left-right (LR). Average standard deviation was 0.45 cm AP and 0.13 cm LR. Inferior CTV average displacement was 0.16 cm AP and 0.01 cm LR. Average standard deviation was 0.17 cm AP and 0.03 cm LR. There was no statistically significant impact of bladder filling on CTV CI in ERB patients (P = 0.551) as opposed to non-ERB patients (P = 0.0421).
  
  
  CONCLUSIONS
  ERBs in the post-prostatectomy setting resulted in increased rectal and CTV stability while negating the effects of bladder filling on CTV stability.
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.
authors.forename: Jeremiah F
authors.initials: JF
authors.lastname: de Leon
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.|Centre For Medical Radiation Physics, University of Wollongong, Wollongong, New South Wales, Australia.|Ingham Institute, Sydney, New South Wales, Australia.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Jameson
authors.affiliation: Central Coast Cancer Centre, Gosford, New South Wales, Australia.|University of New South Wales, Australia.
authors.forename: Apsara
authors.initials: A
authors.lastname: Windsor
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.
authors.forename: Kirrily
authors.initials: K
authors.lastname: Cloak
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.
authors.forename: Sarah
authors.initials: S
authors.lastname: Keats
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.|Ingham Institute, Sydney, New South Wales, Australia.|Medical Physics, School of Physics, University of Sydney, New South Wales, Australia.
authors.forename: Philip
authors.initials: P
authors.lastname: Vial
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.|Centre For Medical Radiation Physics, University of Wollongong, Wollongong, New South Wales, Australia.|Ingham Institute, Sydney, New South Wales, Australia.|Medical Physics, School of Physics, University of Sydney, New South Wales, Australia.|SWSCS, School of Medicine, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
authors.affiliation: Centre For Medical Radiation Physics, University of Wollongong, Wollongong, New South Wales, Australia.|Ingham Institute, Sydney, New South Wales, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalfe
authors.affiliation: Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centres, Sydney, New South Wales, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Sidhom
mesh_terms: D006801:Humans; D007103:Immobilization / Q000295:instrumentation* / Q000379:methods; D008297:Male; D009038:Motion; D056888:Patient Positioning / Q000295:instrumentation / Q000379:methods; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy*; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant / Q000295:instrumentation; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D016896:Treatment Outcome; D047368:Tumor Burden
keywords: endorectal balloon; interfraction motion; post-prostatectomy
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