title: Bile acid malabsorption after pelvic and prostate intensity modulated radiation therapy: an uncommon but treatable condition.
abstract: OBJECTIVE
  Intensity modulated radiation therapy (IMRT) is a significant therapeutic advance in prostate cancer, allowing increased tumor dose delivery and increased sparing of normal tissues. IMRT planning uses strict dose constraints to nearby organs to limit toxicity. Bile acid malabsorption (BAM) is a treatable disorder of the terminal ileum (TI) that presents with symptoms similar to radiation therapy toxicity. It has not been described in patients receiving RT for prostate cancer in the contemporary era. We describe new-onset BAM in men after IMRT for prostate cancer.
  
  
  METHODS
  Diagnosis of new-onset BAM was established after typical symptoms developed, selenium-75 homocholic acid taurine (SeHCAT) scanning showed 7-day retention of <15%, and patients' symptoms unequivocally responded to a bile acid sequestrant. The TI was identified on the original radiation therapy plan, and the radiation dose delivered was calculated and compared with accepted dose-volume constraints.
  
  
  RESULTS
  Five of 423 men treated in a prospective series of high-dose prostate and pelvic IMRT were identified with new onset BAM (median age, 65 years old). All reported having normal bowel habits before RT. The volume of TI ranged from 26-141 cc. The radiation dose received by the TI varied between 11.4 Gy and 62.1 Gy (uncorrected). Three of 5 patients had TI treated in excess of 45 Gy (equivalent dose calculated in 2-Gy fractions, using an α/β ratio of 3) with volumes ranging from 1.6 cc-49.0 cc. One patient had mild BAM (SeHCAT retention, 10%-15%), 2 had moderate BAM (SeHCAT retention, 5%-10%), and 2 had severe BAM (SeHCAT retention, <5%). The 3 patients whose TI received ≥45 Gy developed moderate to severe BAM, whereas those whose TI received <45 Gy had only mild to moderate BAM.
  
  
  CONCLUSIONS
  Radiation delivered to the TI during IMRT may cause BAM. Identification of the TI from unenhanced RT planning computed tomography scans is difficult and may impede accurate dosimetric evaluation. Thorough toxicity assessment and close liaison between oncologist and gastroenterologist allow timely diagnosis and treatment.
authors.affiliation: Academic Urology Unit, Institute of Cancer Research and The Royal Marsden Hospital, London and Sutton, United Kingdom.
authors.forename: Victoria
authors.initials: V
authors.lastname: Harris
authors.forename: Barbara
authors.initials: B
authors.lastname: Benton
authors.forename: Aslam
authors.initials: A
authors.lastname: Sohaib
authors.forename: David
authors.initials: D
authors.lastname: Dearnaley
authors.forename: H Jervoise N
authors.initials: HJ
authors.lastname: Andreyev
mesh_terms: D000368:Aged; D001647:Bile Acids and Salts / Q000378:metabolism*; D006801:Humans; D007082:Ileum / Q000378:metabolism / Q000528:radiation effects*; D008286:Malabsorption Syndromes / Q000000981:diagnostic imaging / Q000209:etiology* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000150:complications* / Q000000981:diagnostic imaging / Q000378:metabolism; D011877:Radionuclide Imaging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods; D013656:Taurocholic Acid / Q000031:analogs & derivatives / Q000493:pharmacokinetics
chemical_list: D001647:Bile Acids and Salts; D013656:Taurocholic Acid; C033638:23-seleno-25-homotaurocholic acid