title: Bladder dose-surface maps and urinary toxicity: Robustness with respect to motion in assessing local dose effects.
abstract: The purpose of this study was to quantify the impact of inter-fraction modifications of bladder during RT of prostate cancer on bladder dose surface maps (DSM). Eighteen patients treated with daily image-guided Tomotherapy and moderate hypofractionation (70-72.8Gy at 2.5-2.6Gy/fr in 28 fractions and full bladder) were considered. Bladder contours were delineated on co-registered daily Megavoltage CT (MVCT) by a single observer and copied on the planning CT to generate dose-volume/surface histograms (DVH/DSH) and bladder DSMs. Discrepancies between planned and daily absorbed doses were analyzed through the average of individual systematic errors, the population systematic errors and the population random errors for the DVH/DSHs and DSMs. In total, 477 DVH/DSH and 472 DSM were available. DSH and DVH showed small population systematic errors of absolute surfaces (<3.4cm(2)) and volumes (<8.4cm(3)) at the highest doses. The dose to the posterior bladder base assessed on DSMs showed a mean systematic error below 1Gy, with population systematic and random errors within 4 and 3Gy, respectively. The region surrounding this area shows higher mean systematic errors (1-3Gy), population systematic (8-11Gy) and random (5-7Gy) errors. In conclusion, DVH/DSH and DSMs are quite stable with respect to inter-fraction variations in the high-dose region, within about 2cm from bladder base. Larger systematic variations occur in the anterior portion and cranially 2.5-3.5cm from the base. Results suggest that dose predictors related to the high dose area (including the trigone dose) are likely to be sufficiently reliable with respect to the expected variations due to variable bladder filling.
authors.affiliation: Medical Physics, San Raffaele Scientific Institute IRCCS, Milan, Italy. Electronic address: palorini.federica@hsr.it.
authors.forename: F
authors.initials: F
authors.lastname: Palorini
authors.affiliation: Medical Physics, Arcispedale S. M. Nuova, Reggio Emilia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Botti
authors.affiliation: Medical Physics, San Raffaele Scientific Institute IRCCS, Milan, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Carillo
authors.affiliation: Medical Software Solutions GmbH, Hagendorn, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Gianolini
authors.affiliation: Medical Physics, San Raffaele Scientific Institute IRCCS, Milan, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Improta
authors.affiliation: Radiotherapy, Arcispedale S. M. Nuova, Reggio Emilia, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Iotti
authors.affiliation: Prostate Cancer Program, Istituto Nazionale dei Tumori IRCCS, Milan, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Rancati
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Cozzarini
authors.affiliation: Medical Physics, San Raffaele Scientific Institute IRCCS, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Fiorino
mesh_terms: D015331:Cohort Studies; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology* / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012669:Seminal Vesicles / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000528:radiation effects; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D014555:Urination Disorders / Q000209:etiology* / Q000517:prevention & control
keywords: Bladder; Dose–surface maps; Inter-fraction motion