title: Adaptive radiation therapy for postprostatectomy patients using real-time electromagnetic target motion tracking during external beam radiation therapy.
abstract: OBJECTIVE
  Using real-time electromagnetic (EM) transponder tracking data recorded by the Calypso 4D Localization System, we report inter- and intrafractional target motion of the prostate bed, describe a strategy to evaluate treatment adequacy in postprostatectomy patients receiving intensity modulated radiation therapy (IMRT), and propose an adaptive workflow.
  
  
  METHODS
  Tracking data recorded by Calypso EM transponders was analyzed for postprostatectomy patients that underwent step-and-shoot IMRT. Rigid target motion parameters during beam delivery were calculated from recorded transponder positions in 16 patients with rigid transponder geometry. The delivered doses to the clinical target volume (CTV) were estimated from the planned dose matrix and the target motion for the first 3, 5, 10, and all fractions. Treatment adequacy was determined by comparing the delivered minimum dose (Dmin) with the planned Dmin to the CTV. Treatments were considered adequate if the delivered CTV Dmin is at least 95% of the planned CTV Dmin.
  
  
  RESULTS
  Translational target motion was minimal for all 16 patients (mean: 0.02 cm; range: -0.12 cm to 0.07 cm). Rotational motion was patient-specific, and maximum pitch, yaw, and roll were 12.2, 4.1, and 10.5°, respectively. We observed inadequate treatments in 5 patients. In these treatments, we observed greater target rotations along with large distances between the CTV centroid and transponder centroid. The treatment adequacy from the initial 10 fractions successfully predicted the overall adequacy in 4 of 5 inadequate treatments and 10 of 11 adequate treatments.
  
  
  CONCLUSIONS
  Target rotational motion could cause underdosage to partial volume of the postprostatectomy targets. Our adaptive treatment strategy is applicable to post-prostatectomy patients receiving IMRT to evaluate and improve radiation therapy delivery.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, MO 63110, USA.
authors.forename: Mingyao
authors.initials: M
authors.lastname: Zhu
authors.forename: Shyam
authors.initials: S
authors.lastname: Bharat
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Michalski
authors.forename: Hiram A
authors.initials: HA
authors.lastname: Gay
authors.forename: Wei-Hsien
authors.initials: WH
authors.lastname: Hou
authors.forename: Parag J
authors.initials: PJ
authors.lastname: Parikh
mesh_terms: D000368:Aged; D004574:Electromagnetic Fields; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011182:Postoperative Care; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012399:Rotation; D016879:Salvage Therapy