title: Margin reduction from image guided radiation therapy for soft tissue sarcoma: Secondary analysis of Radiation Therapy Oncology Group 0630 results.
abstract: OBJECTIVE
  Six imaging modalities were used in Radiation Therapy Oncology Group (RTOG) 0630, a study of image guided radiation therapy (IGRT) for primary soft tissue sarcomas of the extremity. We analyzed all daily patient-repositioning data collected in this trial to determine the impact of daily IGRT on clinical target volume-to-planning target volume (CTV-to-PTV) margin.
  
  
  METHODS
  Daily repositioning data, including shifts in right-left (RL), superior-inferior (SI), and anterior-posterior (AP) directions and rotations for 98 patients enrolled in RTOG 0630 from 18 institutions were analyzed. Patients were repositioned daily on the basis of bone anatomy by using pretreatment images, including kilovoltage orthogonal images (KVorth), megavoltage orthogonal images (MVorth), KV fan-beam computed tomography (KVCT), KV cone beam CT (KVCB), MV fan-beam CT (MVCT), and MV cone beam CT (MVCB). Means and standard deviations (SDs) for each shift and rotation were calculated for each patient and for each IGRT modality. The Student's t tests and F-tests were performed to analyze the differences in the means and SDs. Necessary CTV-to-PTV margins were estimated.
  
  
  RESULTS
  The repositioning shifts and day-to-day variations were large and generally similar for the 6 imaging modalities. Of the 2 most commonly used modalities, MVCT and KVorth, there were no statistically significant differences in the shifts and rotations (P = .15 and .59 for the RL and SI shifts, respectively; and P = .22 for rotation), except for shifts in AP direction (P = .002). The estimated CTV-to-PTV margins in the RL, SI, and AP directions would be 13.0, 10.4, and 11.7 mm from MVCT data, respectively, and 13.1, 8.6, and 10.8 mm from KVorth data, respectively, indicating that margins substantially larger than 5 mm used with daily IGRT would be required in the absence of IGRT.
  
  
  CONCLUSIONS
  The observed large daily repositioning errors and the large variations among institutions imply that daily IGRT is necessary for this tumor site, particularly in multi-institutional trials. Otherwise, a CTV-to-PTV margin of 1.5 cm is required to account for daily setup variations.
authors: Medical College of Wisconsin, Milwaukee, Wisconsin. Electronic address: ali@mcw.edu.
authors: X Allen
authors: XA
authors: Li
authors: Medical College of Wisconsin, Milwaukee, Wisconsin.
authors: Xiaojian
authors: X
authors: Chen
authors: NRG Oncology Statistics and Data Management Center, Philadelphia, Pennsylvania.
authors: Qiang
authors: Q
authors: Zhang
authors: Duke University Medical Center, Durham, North Carolina.
authors: David G
authors: DG
authors: Kirsch
authors: Mayo Clinic, Rochester, Minnesota.
authors: Ivy
authors: I
authors: Petersen
authors: Massachusetts General Hospital, Boston, Massachusetts.
authors: Thomas F
authors: TF
authors: DeLaney
authors: McGill University Health Centre, Montreal, Quebec, Canada.
authors: Carolyn R
authors: CR
authors: Freeman
authors: H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida.
authors: Andy
authors: A
authors: Trotti
authors: University of Utah, Salt Lake City, Utah.
authors: Ying
authors: Y
authors: Hitchcock
authors: Medical College of Wisconsin, Milwaukee, Wisconsin.
authors: Meena
authors: M
authors: Bedi
authors: Mayo Clinic, Rochester, Minnesota.
authors: Michael
authors: M
authors: Haddock
authors: Roswell Park Cancer Institute, Buffalo, New York.
authors: Kilian
authors: K
authors: Salerno
authors: Cross Cancer Institute - University of Alberta, Edmonton, Alberta, Canada.
authors: George
authors: G
authors: Dundas
authors: Rush University Medical Center, Chicago, Illinois.
authors: Dian
authors: D
authors: Wang
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012509:Sarcoma / Q000532:radiotherapy*