title: High-dose-rate endorectal brachytherapy in the treatment of locally advanced rectal carcinoma: technical aspects.
abstract: OBJECTIVE
  In this era of new radiation technologies and tumor imaging, a high-dose-rate endorectal brachytherapy has been developed and tested in a phase I/II study of advanced rectal tumors. In this article, we report technical aspects of the treatment modality.
  
  
  METHODS
  Forty-nine patients underwent staging with endoscopic endorectal ultrasound, and the tumor dimensions were determined with MRI of the pelvis. Patients with resectable rectal cancer (staged T2, T3, or early T4) were treated with preoperative high-dose-rate endorectal brachytherapy followed by surgery 6-8 weeks later. Under direct rectoscopy, radio-opaque clips were used to mark the tumor margins. The treatment planning was done with the use of a CT simulator, and the treatment was delivered using a flexible endorectal applicator with eight catheters arranged around the circumference of the applicator and a high-dose-rate brachytherapy remote afterloading system with an Iridium-192 source. Isodose distributions were generated by the Plato planning system (Nucletron B.V., Veenendaal, The Netherlands) and digitally reconstructed radiographs were used as references for daily treatment. A tumor dose of 26 Gy in four fractions was prescribed, and intramesorectal deposits were documented on the magnetic resonance images.
  
  
  RESULTS
  Forty-nine patients received planned treatment, and all but 2 patients underwent planned surgery. The pathology specimens showed a complete macroscopic response in 64% of the patients and tumor downstaging in 67% of the patients.
  
  
  CONCLUSIONS
  Advances in tumor imaging and 3D treatment planning systems allow for better tumor mapping and dose planning. The use of a multichannel flexible endorectal applicator leads to tumor downstaging before surgery in patients with resectable locally advanced rectal carcinomas. The technique used in our center was practical and validated by this study.
authors.affiliation: Division of Radiation Oncology, McGill University Health Centre, Montreal, Canada. te.vuong@muhc.mcgill.ca
authors.forename: Té
authors.initials: T
authors.lastname: Vuong
authors.forename: Slobodan
authors.initials: S
authors.lastname: Devic
authors.forename: Belal
authors.initials: B
authors.lastname: Moftah
authors.forename: Michael
authors.initials: M
authors.lastname: Evans
authors.forename: Ervin B
authors.initials: EB
authors.lastname: Podgorsak
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D006801:Humans; D008297:Male; D010818:Practice Patterns, Physicians'; D011859:Radiography; D011878:Radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D012720:Severity of Illness Index; D016896:Treatment Outcome