title: Prostate bed target interfractional motion using RTOG consensus definitions and daily CT on rails : Does target motion differ between superior and inferior portions of the clinical target volume?
abstract: OBJECTIVE
  Using high-quality CT-on-rails imaging, the daily motion of the prostate bed clinical target volume (PB-CTV) based on consensus Radiation Therapy Oncology Group (RTOG) definitions (instead of surgical clips/fiducials) was studied. It was assessed whether PB motion in the superior portion of PB-CTV (SUP-CTV) differed from the inferior PB-CTV (INF-CTV).
  
  
  METHODS
  Eight pT2-3bN0-1M0 patients underwent postprostatectomy intensity-modulated radiotherapy, totaling 300 fractions. INF-CTV and SUP-CTV were defined as PB-CTV located inferior and superior to the superior border of the pubic symphysis, respectively. Daily pretreatment CT-on-rails images were compared to the planning CT in the left-right (LR), superoinferior (SI), and anteroposterior (AP) directions. Two parameters were defined: "total PB-CTV motion" represented total shifts from skin tattoos to RTOG-defined anatomic areas; "PB-CTV target motion" (performed for both SUP-CTV and INF-CTV) represented shifts from bone to RTOG-defined anatomic areas (i. e., subtracting shifts from skin tattoos to bone).
  
  
  RESULTS
  Mean (± standard deviation, SD) total PB-CTV motion was -1.5 (± 6.0), 1.3 (± 4.5), and 3.7 (± 5.7) mm in LR, SI, and AP directions, respectively. Mean (± SD) PB-CTV target motion was 0.2 (±1.4), 0.3 (±2.4), and 0 (±3.1) mm in the LR, SI, and AP directions, respectively. Mean (± SD) INF-CTV target motion was 0.1 (± 2.8), 0.5 (± 2.2), and 0.2 (± 2.5) mm, and SUP-CTV target motion was 0.3 (± 1.8), 0.5 (± 2.3), and 0 (± 5.0) mm in LR, SI, and AP directions, respectively. No statistically significant differences between INF-CTV and SUP-CTV motion were present in any direction.
  
  
  CONCLUSIONS
  There are no statistically apparent motion differences between SUP-CTV and INF-CTV. Current uniform planning target volume (PTV) margins are adequate to cover both portions of the CTV.
authors.affiliation: Department of Radiation Oncology, University of Nebraska Medical Center, NE 68198, Omaha, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Verma
authors.affiliation: Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Shifeng
authors.initials: S
authors.lastname: Chen
authors.affiliation: Department of Radiation Oncology, University of Nebraska Medical Center, NE 68198, Omaha, USA.
authors.forename: Sumin
authors.initials: S
authors.lastname: Zhou
authors.affiliation: Department of Radiation Oncology, University of Nebraska Medical Center, NE 68198, Omaha, USA.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Enke
authors.affiliation: Department of Radiation Oncology, University of Nebraska Medical Center, NE 68198, Omaha, USA. awahl@unmc.edu.
authors.forename: Andrew O
authors.initials: AO
authors.lastname: Wahl
mesh_terms: D000368:Aged; D016477:Artifacts; D019983:Guideline Adherence; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D056888:Patient Positioning / Q000592:standards*; D017410:Practice Guidelines as Topic; D018787:Radiation Oncology / Q000592:standards; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000592:standards*; D061089:Radiotherapy, Image-Guided / Q000592:standards*; D050397:Radiotherapy, Intensity-Modulated / Q000592:standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000592:standards*; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects; D014481:United States
keywords: Computed tomography; Prostate cancer; Prostatectomy; Radiotherapy, intensity modulated; Toxicity