title: Three-dimensional analysis of recurrence patterns in rectal cancer: the cranial border in hypofractionated preoperative radiotherapy can be lowered.
abstract: OBJECTIVE
  The aim of this study was to determine whether and where the radiotherapy (RT) clinical target volume (CTV) could be reduced in short-course preoperative treatment of rectal cancer patients.
  
  
  METHODS
  Patients treated in the Dutch total mesorectal excision trial, with a local recurrence were analyzed. For 94 (25 who underwent radiation therapy 69 who did not) of 114 patients with a local recurrence, the location of the recurrence was placed in a three-dimensionalthree (3D) model. The data in the 3D model were correlated to the clinical trial data to distinguish a group of patients eligible for CTV reduction. Effects of CTV reduction on dose to the small bowel was tested retrospectively in a dataset of 8 patients with three-field conformal plans and intensity-modulated RT (IMRT).
  
  
  RESULTS
  The use of preoperative RT mainly reduces anastomotic, lateral, and perineal recurrences. In patients without primary nodal involvement, no recurrences were found cranially of the S2-S3 interspace, irrespective of the delivery of RT. In patients without primary nodal involvement and a negative circumferential resection margin (CRM), only one recurrence was found cranial to the S2-S3 interspace. With a cranially reduced CTV to the S2-S3 interspace, over 60% reduction in absolute small bowel exposure at dose levels from 15 to 35 Gy could be achieved with three-field conventional RT, increasing to 80% when IMRT is also added.
  
  
  CONCLUSIONS
  The cranial border of the CTV can safely be lowered for patients without expected nodal or CRM involvement, yielding a significant reduction of dose to the small bowel. Therefore, a significant reduction of acute and late toxicity can be expected.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Jasper
authors.initials: J
authors.lastname: Nijkamp
authors.forename: Miranda
authors.initials: M
authors.lastname: Kusters
authors.forename: Regina G H
authors.initials: RG
authors.lastname: Beets-Tan
authors.forename: Hendrik
authors.initials: H
authors.lastname: Martijn
authors.forename: Geerard L
authors.initials: GL
authors.lastname: Beets
authors.forename: Cornelis J H
authors.initials: CJ
authors.lastname: van de Velde
authors.forename: Corrie A M
authors.initials: CA
authors.lastname: Marijnen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003131:Combined Modality Therapy / Q000379:methods; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007421:Intestine, Small / Q000528:radiation effects; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging*; D009426:Netherlands; D058958:Organs at Risk / Q000528:radiation effects; D011832:Radiation Injuries / Q000517:prevention & control; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery; D047368:Tumor Burden; D055815:Young Adult