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BioMed Research International
Volume 2014, Article ID 578243, 6 pages
http://dx.doi.org/10.1155/2014/578243
Clinical Study

Dosimetric Coverage of the External Anal Sphincter by 3-Dimensional Conformal Fields in Rectal Cancer Patients Receiving Neoadjuvant Chemoradiation: Implications for the Concept of Sphincter-Preserving Radiation Therapy

1Radiation Oncology, City of Hope Medical Center, 1500 East Duarte Road, Duarte, CA 91010, USA
2Colorectal Surgery, City of Hope Medical Center, 1500 East Duarte Road, Duarte, CA 91010, USA

Received 26 April 2014; Accepted 7 June 2014; Published 25 June 2014

Academic Editor: Tsair-Fwu Lee

Copyright © 2014 Yi-Jen Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background. We evaluated the anatomic location of the external anal sphincter (EAS) to pelvic bony landmarks related to 3-dimensional conformal radiotherapy (3DRT) and studied the dosimetric coverage of the EAS in patients undergoing neoadjuvant chemoradiation for rectal cancer. Methods. Sixty-four consecutive rectal cancer patients treated with neoadjuvant chemoradiation were included. All patients were treated in a prone position on a bellyboard by 3DRT. The inferior border of the RT fields was at least 3–5 cm inferior to the gross tumorous volume (GTV) or at the inferior border of the obturator foramen (IBOF), whichever was more inferior. The EAS was contoured and dose distributions were determined using dose-volume histograms. Results. In 53 out of 64 cases (82.8%), the EAS was completely inferior to the IBOF. In the remaining 11 cases, the EAS was either overlapping the IBOF (10 cases; 15.6%) or completely superior to the IBOF (1 case; 1.7%). The average mean dose delivered to the EAS was 2795 cGy. Lower mean doses were delivered to the EAS when the center of the EAS was located more distant from the GTV. Conclusions. Meticulous planning to define the inferior border of the RT field is recommended to avoid irradiating the EAS.