Three-dimensional analysis of recurrence patterns in rectal cancer: the cranial border in hypofractionated preoperative radiotherapy can be lowered.
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.
Nijkamp
Jasper
J
Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
Kusters
Miranda
M
Beets-Tan
Regina G H
RG
Martijn
Hendrik
H
Beets
Geerard L
GL
van de Velde
Cornelis J H
CJ
Marijnen
Corrie A M
CA
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