title: A quality control study of the accuracy of patient positioning in irradiation of pelvic fields.
abstract: OBJECTIVE
  Determining and improving the accuracy of patient positioning in pelvic fields.
  
  
  METHODS
  Small pelvic fields were studied in 16 patients treated for urological cancers using a three-field isocentric technique. Large pelvic fields were studied in 17 gynecological cancer patients treated with anterior and posterior (AP-PA) parallel opposed fields. Quantitative analysis of 645 megavolt images and comparison to 82 simulation images were carried out.
  
  
  RESULTS
  Small pelvic fields: for the position of the patient in the field, standard deviations of the difference between simulation (SIM) and treatment (MV) images were 3.4 mm in the lateral direction, 5.3 mm in the cranio-caudal direction, and 4.8 mm in the ventro-dorsal direction. Alterations in the positioning technique were made and tested. Large pelvic fields: differences between simulation and treatment images for the position of the patient in the field were 4 mm [1 standard deviation (SD)] in the lateral direction and 6.5 mm in the cranio-caudal direction. A systematic shift of the treatment field in the cranial direction had occurred in the majority of patients. A positioning technique using laser lines and marking of the caudal field border was shown to be more accurate.
  
  
  CONCLUSIONS
  Studies of positioning accuracy in routine irradiation techniques are needed to obtain data for definition of the margins for each treatment site at each institution. Random variations should be kept at a minimum by monitoring and improving positioning techniques. Treatment verification by megavolt imaging or film should be used to detect and correct systematic variations early in the treatment series.
authors.affiliation: Department of Radiation Oncology, Dr. Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
authors.forename: C L
authors.initials: CL
authors.lastname: Creutzberg
authors.forename: V G
authors.initials: VG
authors.lastname: Althof
authors.forename: M D
authors.initials: MD
authors.lastname: de Hoog
authors.forename: A G
authors.initials: AG
authors.lastname: Visser
authors.forename: H
authors.initials: H
authors.lastname: Huizenga
authors.forename: A
authors.initials: A
authors.lastname: Wijnmaalen
authors.forename: P C
authors.initials: PC
authors.lastname: Levendag
mesh_terms: D016889:Endometrial Neoplasms / Q000532:radiotherapy; D005069:Evaluation Studies as Topic; D005260:Female; D005500:Follow-Up Studies; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D011187:Posture; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011786:Quality Control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards*; D014057:Tomography, X-Ray Computed; D001749:Urinary Bladder Neoplasms / Q000532:radiotherapy; D014571:Urologic Neoplasms / Q000532:radiotherapy*; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy