title: A dosimetric evaluation of using a single treatment plan for multiple treatment fractions within a given applicator insertion in gynecologic brachytherapy.
abstract: OBJECTIVE
  To evaluate the dosimetric impact of using one treatment plan for multiple fractions from a single tandem and ring applicator insertion of high-dose-rate brachytherapy for cervical cancer.
  
  
  METHODS
  Thirteen cervical cancer patients undergoing high-dose-rate brachytherapy were followed. Patients received the total dose from a single applicator insertion in two fractions, given with at least 6 hours apart within 24 hours. The treatment plan was based on a CT scan taken before the first treatment fraction. A second CT was obtained before the second treatment fraction. The co-registered image series were used to evaluate the dosimetric impact of using a single treatment plan for both fractions. Applicator and catheters were measured to quantify interfraction displacement.
  
  
  RESULTS
  When the Day 1 plan was applied to the Day 2 images, high-risk clinical target volume (HR-CTV) coverage was reduced by as much as 17.4 percentage points. The mean decrease was 9.4 ± 5.0 percentage points (p < 0.0001). The rectum V75 increase was significant (p = 0.03), whereas the bladder V75 increase was not significant (p = 0.28). Volume changes in the HR-CTV contour from Day 1 to Day 2 were also observed (p = 0.29). Maximum applicator and catheter displacements of 10-30mm were seen, from Day 1 to Day 2.
  
  
  CONCLUSIONS
  When the Day 1 plan was used on the Day 2, the HR-CTV coverage decreased significantly (p < 0.0001). Our study establishes the need for institutions to evaluate the necessity for replanning based on imaging obtained before each treatment fraction for their gynecologic brachytherapy techniques.
authors.affiliation: Department of Radiation Oncology, University of California San Francisco, San Francisco, CA. Electronic address: pinnaduwageds@radonc.ucsf.edu.
authors.forename: Dilini S
authors.initials: DS
authors.lastname: Pinnaduwage
authors.forename: J Adam
authors.initials: JA
authors.lastname: Cunha
authors.forename: Vivian
authors.initials: V
authors.lastname: Weinberg
authors.forename: Devan
authors.initials: D
authors.lastname: Krishnamurthy
authors.forename: Marc
authors.initials: M
authors.lastname: Nash
authors.forename: I-Chow
authors.initials: IC
authors.lastname: Hsu
authors.forename: Jean
authors.initials: J
authors.lastname: Pouliot
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000379:methods*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011874:Radiometry; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
keywords: Cervical cancer; HDR brachytherapy; Interfraction dosimetry; Tandem–ring