title: Comparison of margins, integral dose and interfraction target coverage with image-guided radiotherapy compared with non-image-guided radiotherapy for bladder cancer.
abstract: OBJECTIVE
  To measure the difference in cumulative doses received by the bladder (target) and integral doses with different clinical target volume (CTV) to planning target volume (PTV) margins, comparing set-up to skin tattoos versus image-guided radiotherapy to bone or soft tissue.
  
  
  METHODS
  Four plans were generated on each planning computed tomography dataset using the CTV with 5, 10, 15, 20 mm PTV margins using a three-dimensional conformal four-field technique. Set-up data based on skin, bone and soft tissue to the bladder on pre-treatment cone beam computed tomography (CBCT) were recorded. In total, 316 CBCTs were evaluable from 10 bladder cancer patients. Each CBCT was fused to the planning computed tomography dataset using the isocentre corresponding to each of the three pre-treatment matching conditions. The target was contoured on each CBCT and called the CTV of the day and the plan was re-calculated to determine the dose to this.
  
  
  RESULTS
  The mean D95 with CTV to PTV margins of 5, 10, 15 and 20 mm for skin set-up was 89.4, 93.0, 97.2, 98.6; for bone 88.8, 92.6, 96.7, 98.6; and for soft tissue 96.3, 98.6, 98.7, 99.5. With soft-tissue matching, the mean (standard deviation) volume of normal tissue receiving 5 Gy with 5, 10, 15 and 20 mm margins was 3899 (1022), 4561 (1142), 5663 (1304) and 6315 (1426) in cm(3).
  
  
  CONCLUSIONS
  Soft-tissue matching results in superior target coverage and a reduced integral dose to the surrounding tissues. With soft-tissue matching, increasing CTV to PTV margins progressively beyond 5 mm results in modest improvement in CTV coverage, but a large increase in integral dose.
authors.affiliation: Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Victoria, Australia. Electronic address: farshad.foroudi@petermac.org.
authors.forename: F
authors.initials: F
authors.lastname: Foroudi
authors.affiliation: Radiation Therapy Services, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Pham
authors.affiliation: Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Bressel
authors.affiliation: Physical Sciences, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Hardcastle
authors.affiliation: Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Victoria, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Gill
authors.affiliation: Sir Peter MacCallum Department of Oncology, University of Melbourne, Victoria, Australia; Physical Sciences, Peter MacCallum Cancer Center, Melbourne, Victoria, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Kron
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy*
keywords: Bladder cancer; dose accumulation; image-guided radiotherapy; margins; radiation dose