title: Proposed rectal dose constraints for patients undergoing definitive whole pelvic radiotherapy for clinically localized prostate cancer.
abstract: OBJECTIVE
  Although several institutions have reported rectal dose constraints according to threshold toxicity, the plethora of trials has resulted in multiple, confusing dose-volume histogram recommendations. A set of standardized, literature-based constraints for patients undergoing whole pelvic radiotherapy (RT) for prostate cancer would help guide the practice of prostate RT. The purpose of this study was to develop these constraints, demonstrate that they are achievable, and assess the corresponding rectal toxicity.
  
  
  METHODS
  An extensive literature search identified eight key studies relating dose-volume histogram data to rectal toxicity. A correction factor was developed to address differences in the anatomic definition of the rectum across studies. The dose-volume histogram constraints recommended by each study were combined to generate the constraints. The data from all patients treated with definitive intensity-modulated RT were then compared against these constraints. Acute rectal toxicity was assessed.
  
  
  RESULTS
  A continuous, proposed rectal dose-constraint curve was generated. Intensity-modulated RT not only met this constraint curve, but also was able to achieve at least 30-40% lower dose to the rectum. The preliminary clinical results were also positive: 50% of patients reported no acute bowel toxicity, 33% reported Grade 1 toxicity, and 17% reported Grade 2 toxicity. No patients reported Grade 3-4 acute rectal toxicity.
  
  
  CONCLUSIONS
  In this study, we developed a set of proposed rectal dose constraints. This allowed for volumetric assessment of the dose-volume relationship compared with single dose-volume histogram points. Additional research will be performed to validate this threshold as a class solution for rectal dose constraints.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, School of Medicine, San Francisco, CA 94115, USA. lindachan@radonc.ucsf.edu
authors.forename: Linda W
authors.initials: LW
authors.lastname: Chan
authors.forename: Ping
authors.initials: P
authors.lastname: Xia
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gottschalk
authors.forename: Michelle
authors.initials: M
authors.lastname: Akazawa
authors.forename: Matthew
authors.initials: M
authors.lastname: Scala
authors.forename: Barby
authors.initials: B
authors.lastname: Pickett
authors.forename: I-Chow
authors.initials: IC
authors.lastname: Hsu
authors.forename: Joycelyn
authors.initials: J
authors.lastname: Speight
authors.forename: Mack
authors.initials: M
authors.lastname: Roach
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000473:pathology / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D012007:Rectum / Q000033:anatomy & histology / Q000528:radiation effects*; D047368:Tumor Burden