title: Dose-surface maps identifying local dose-effects for acute gastrointestinal toxicity after radiotherapy for prostate cancer.
abstract: OBJECTIVE
  We evaluated dose distributions in the anorectum and its relation to acute gastrointestinal toxicities using dose surface maps in an image-guided (IG) IMRT and 3D-conformal radiotherapy (3D-CRT) population.
  
  
  METHODS
  For patients treated to 78 Gy with IG-IMRT (n=260) or 3D-CRT (n=215), for whom acute toxicity data were available, three types of surface maps were calculated: (1) total anorectum using regular intervals along a central axis with perpendicular slices, (2) the rectum next to the prostate, and (3) the anal canal (horizontal slicing). For each toxicity, an average dose map was calculated for patients with and without the toxicity and subsequently dose difference maps were constructed, 3D-CRT and IG-IMRT separately. P-values were based on permutation tests.
  
  
  RESULTS
  Dose distributions in patients with grade ⩾2 acute proctitis were significantly different from dose distributions in patients without toxicity, for IG-IMRT and 3D-CRT. At the cranial and posterior rectal site, in areas receiving moderate dose levels (≈25-50 Gy), dose differences up to 10 Gy were identified for IG-IMRT. For pain, cramps, incontinence, diarrhea and mucus loss significant differences were found as well.
  
  
  CONCLUSIONS
  We demonstrated significant relationships between acute rectal toxicity and local dose distributions. This may serve as a basis for subsequent dose-effect modeling in IG-IMRT, and improved dose constraints in current clinical practice.
authors.affiliation: Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands.
authors.forename: Ruud C
authors.initials: RC
authors.lastname: Wortel
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Marnix G
authors.initials: MG
authors.lastname: Witte
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Uulke A
authors.initials: UA
authors.lastname: van der Heide
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Floris J
authors.initials: FJ
authors.lastname: Pos
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Joos V
authors.initials: JV
authors.lastname: Lebesque
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.affiliation: Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands.
authors.forename: Luca
authors.initials: L
authors.lastname: Incrocci
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: w.heemsbergen@nki.nl.
authors.forename: Wilma D
authors.initials: WD
authors.lastname: Heemsbergen
mesh_terms: D000368:Aged; D001003:Anal Canal / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005767:Gastrointestinal Diseases / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D012007:Rectum / Q000528:radiation effects
keywords: Dose surface maps; Gastrointestinal; Prostate cancer; Radiotherapy; Toxicity