title: Bladder spatial-dose descriptors correlate with acute urinary toxicity after radiation therapy for prostate cancer.
abstract: OBJECTIVE
  To assess bladder spatial-dose parameters predicting acute urinary toxicity after radiotherapy for prostate cancer (PCa) through a pixel-wise method for analysis of bladder dose-surface maps (DSMs).
  
  
  METHODS
  The final cohort of a multi-institutional study, consisting of 539 patients with PCa treated with conventionally (CONV:1.8-2Gy/fr) or moderately hypo-fractionated radiotherapy (HYPO:2.2-2.7Gy/fr) was considered. Urinary toxicity was evaluated through the International Prostate Symptoms Score (IPSS) administered before and after radiotherapy. IPSS increases ⩾10 and 15 points at the end of radiotherapy (ΔIPSS⩾10 and ΔIPSS⩾15) were chosen as endpoints. Average DSMs (corrected into 2Gy-equivalent doses) of patients with/without toxicity were compared through a pixel-wise method. This allowed the extraction of selected spatial descriptors discriminating between patients with/without toxicity. Previously logistic models based on dose-surface histograms (DSH) were considered and replaced with DSM descriptors. Discrimination power, calibration and log-likelihood were considered to evaluate the impact of the inclusion of spatial descriptors.
  
  
  RESULTS
  Data of 375/539 patients were available. ΔIPSS⩾10 was recorded in 76/375 (20%) patients, while 30/375 (8%) experienced ΔIPSS⩾15. The posterior dose at 12mm from the bladder base (roughly corresponding to the trigone region) resulted significantly associated to toxicity in the whole/HYPO populations. The cranial extension of the 75Gy isodose along the bladder central axis was the best DSM-based predictor in CONV patients. Multi-variable models including DSM descriptors showed better discrimination (AUC=0.66-0.77) when compared to DSH-based models (AUC=0.58-0.71) and higher log-likelihoods.
  
  
  CONCLUSIONS
  DSMs are correlated with the risk of acute GU toxicity. The incorporation of spatial descriptors improves discrimination and log-likelihood of multi-variable models including dosimetric and clinical parameters.
authors: Medical Physics, San Raffaele Scientific Institute, Milano, Italy. Electronic address: ilaria.improta@gmail.com.
authors: I
authors: I
authors: Improta
authors: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors: F
authors: F
authors: Palorini
authors: Radiotherapy, San Raffaele Scientific Institute, Milano, Italy.
authors: C
authors: C
authors: Cozzarini
authors: Prostate Cancer Program, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors: T
authors: T
authors: Rancati
authors: Radiation Oncology 1, Fondazione IRCCS Istituto Nazionale dei Tumori, Milano, Italy.
authors: B
authors: B
authors: Avuzzi
authors: Radiotherapy, Ospedale Regionale U.Parini - AUSL Valle d'Aosta, Aosta, Italy.
authors: P
authors: P
authors: Franco
authors: Radiotherapy, Ospedale Bellaria, Bologna, Italy.
authors: C
authors: C
authors: Degli Esposti
authors: Radiotherapy, IRCCS-Candiolo, Candiolo (TO), Italy.
authors: E
authors: E
authors: Del Mastro
authors: Radiotherapy, Ospedale ASL9, Ivrea, Italy.
authors: G
authors: G
authors: Girelli
authors: Radiation Therapy Unit, Department of Oncology and Advanced Technology, ASMN Hospital IRCCS, Reggio Emilia, Italy.
authors: C
authors: C
authors: Iotti
authors: Radiotherapy, Cliniche Gavazzeni-Humanitas, Bergamo, Italy.
authors: V
authors: V
authors: Vavassori
authors: Radiation Oncology 1, Fondazione IRCCS Istituto Nazionale dei Tumori, Milano, Italy; Clinical Sciences and Community Health, University of Milan, Milan, Italy.
authors: R
authors: R
authors: Valdagni
authors: Medical Physics, San Raffaele Scientific Institute, Milano, Italy.
authors: C
authors: C
authors: Fiorino
mesh_terms: D000368:Aged; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011878:Radiotherapy / Q000009:adverse effects*; D001743:Urinary Bladder / Q000528:radiation effects*
keywords: Acute urinary toxicity; Bladder spatial-dose descriptors; Dose-surface maps; Prostate radiotherapy