title: Prospective Validation of a High Dimensional Shape Model for Organ Motion in Intact Cervical Cancer.
abstract: Validated models are needed to justify strategies to define planning target volumes (PTVs) for intact cervical cancer used in clinical practice. Our objective was to independently validate a previously published shape model, using data collected prospectively from clinical trials.
  
  
  
  We analyzed 42 patients with intact cervical cancer treated with daily fractionated pelvic intensity modulated radiation therapy and concurrent chemotherapy in one of 2 prospective clinical trials. We collected online cone beam computed tomography (CBCT) scans before each fraction. Clinical target volume (CTV) structures from the planning computed tomography scan were cast onto each CBCT scan after rigid registration and manually redrawn to account for organ motion and deformation. We applied the 95% isodose cloud from the planning computed tomography scan to each CBCT scan and computed any CTV outside the 95% isodose cloud. The primary aim was to determine the proportion of CTVs that were encompassed within the 95% isodose volume. A 1-sample t test was used to test the hypothesis that the probability of complete coverage was different from 95%. We used mixed-effects logistic regression to assess effects of time and patient variability.
  
  
  
  The 95% isodose line completely encompassed 92.3% of all CTVs (95% confidence interval, 88.3%-96.4%), not significantly different from the 95% probability anticipated a priori (P=.19). The overall proportion of missed CTVs was small: the grand mean of covered CTVs was 99.9%, and 95.2% of misses were located in the anterior body of the uterus. Time did not affect coverage probability (P=.71).
  
  
  
  With the clinical implementation of a previously proposed PTV definition strategy based on a shape model for intact cervical cancer, the probability of CTV coverage was high and the volume of CTV missed was low. This PTV expansion strategy is acceptable for clinical trials and practice; however, we recommend daily image guidance to avoid systematic large misses in select patients.
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California.
authors: Casey W
authors: CW
authors: Williamson
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California.
authors: Garrett
authors: G
authors: Green
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California.
authors: Sonal S
authors: SS
authors: Noticewala
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California.
authors: Nan
authors: N
authors: Li
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California.
authors: Hanjie
authors: H
authors: Shen
authors: Division of Biostatistics and Bioinformatics, Department of Family Medicine and Public Health, University of California, San Diego, La Jolla, California.
authors: Florin
authors: F
authors: Vaida
authors: Department of Radiation Medicine and Applied Sciences, University of California, San Diego, La Jolla, California. Electronic address: lmell@ucsd.edu.
authors: Loren K
authors: LK
authors: Mell
mesh_terms: D000328:Adult; D001918:Brachytherapy; D054893:Cone-Beam Computed Tomography; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008875:Middle Aged; D009038:Motion; D009068:Movement; D015588:Observer Variation; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*