title: First application of a pixel-wise analysis on bladder dose-surface maps in prostate cancer radiotherapy.
abstract: To develop a method for investigating local dose effects on the bladder after prostate cancer radiotherapy based on dose-surface maps (DSMs).
  
  
  
  DSMs of patients included in a prospective study (DUE01) were generated by virtually cutting bladder contours at the points intersecting the sagittal plane passing through its center-of-mass: maps were laterally normalized and aligned at the posterior inferior point. The average DSMs of patients with/without toxicity, the DSMs of differences and t statistic were used to select regions better discriminating patients with toxicity. A total of 72 patients with no/mild urinary symptoms before radiotherapy and who were treated with moderate hypo-fractionation (2.5-2.65Gy/fr, 70-74Gy) were considered, and the endpoint was an International Prostate Symptoms Score (IPSS)⩾15 at the end of therapy (IPSSend⩾15, n=25/72).
  
  
  
  The DSMs of patients with/without toxicity were significantly different (p<0.05). The percentage of bladder circumference receiving >50-70Gy at 5-7mm from the base was associated with an IPSSend⩾15 (odds ratios: 1.03-1.07). Different patterns were recognized for specific symptoms. With frequency/urgency, a quasi-threshold effect on the absolute posterior dose at 5-12mm from the base (2Gy equivalent doses=80-82Gy, α/β=3-5Gy) was observed.
  
  
  
  Local-dose effects for acute symptoms were detected in a group of patients treated within a moderately hypo-fractionated protocol. The results for frequency/urgency were consistent with a threshold effect on the trigone.
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Palorini
authors.affiliation: Radiotherapy, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Cozzarini
authors.affiliation: Medical Software Solutions GmbH, Switzerland.
authors.forename: Stefano
authors.initials: S
authors.lastname: Gianolini
authors.affiliation: Medical Physics, Arcispedale S.M. Nuova, Reggio Emilia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Botti
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Viviana
authors.initials: V
authors.lastname: Carillo
authors.affiliation: Radiation Oncology Unit, Arcispedale S.M. Nuova, Reggio Emilia, Italy.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Iotti
authors.affiliation: Prostate Cancer Program, Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Rancati
authors.affiliation: Prostate Cancer Program, Istituto Nazionale dei Tumori, Milan, Italy; Radiation Oncology 1, Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Valdagni
authors.affiliation: Medical Physics, San Raffaele Scientific Institute, Milan, Italy. Electronic address: fiorino.claudio@hsr.it.
authors.forename: Claudio
authors.initials: C
authors.lastname: Fiorino
mesh_terms: D000368:Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D001743:Urinary Bladder / Q000528:radiation effects*
keywords: Dose–volume effects; Prostate cancer; Radiotherapy; Urinary toxicity