title: An evaluation of intrafraction motion of the prostate in the prone and supine positions using electromagnetic tracking.
abstract: OBJECTIVE
  To evaluate differences in target motion during prostate irradiation in the prone versus supine position using electromagnetic tracking to measure prostate mobility.
  
  
  METHODS
  Twenty patients received prostate radiotherapy in the supine position utilizing the Calypso Localization System® for prostate positioning and monitoring. For each patient, 10 treatment fractions were followed by a session in which the patient was repositioned prone, and prostate mobility was tracked. The fraction of time that the prostate was displaced by >3, 5, 7, and 10mm was calculated for each patient, for both positions (400 tracking sessions).
  
  
  RESULTS
  Clear patterns of respiratory motion were seen in the prone tracks due to the influence of increased abdominal motion. Averaged over all patients, the prostate was displaced >3 and 5mm for 37.8% and 10.1% of the total tracking time in the prone position, respectively. In the supine position, the prostate was displaced >3 and 5mm for 12.6% and 2.9%, respectively. With both patient setups, inferior and posterior drifts of the prostate position were observed. Averaged over all prone tracking sessions, the prostate was displaced >3mm in the posterior and inferior directions for 11.7% and 9.5% of the total time, respectively.
  
  
  CONCLUSIONS
  With real-time tracking of the prostate, it is possible to study the effects of different setup positions on the prostate mobility. The percentage of time the prostate moved >3 and 5mm was increased by a factor of three in the prone versus supine position. For larger displacements (>7 mm) no difference in prostate mobility was observed between prone and supine positions. To reduce rectal toxicity, radiotherapy in the prone position may be a suitable alternative provided respiratory motion is accounted for during treatment. Acute and late toxicity results remain to be evaluated for both patient positions.
authors: Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA. Amish.Shah@orlandohealth.com
authors: Amish P
authors: AP
authors: Shah
authors: Patrick A
authors: PA
authors: Kupelian
authors: Twyla R
authors: TR
authors: Willoughby
authors: Katja M
authors: KM
authors: Langen
authors: Sanford L
authors: SL
authors: Meeks
mesh_terms: D019583:Dose Fractionation, Radiation; D055590:Electromagnetic Phenomena; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009038:Motion; D016684:Prone Position; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012119:Respiration; D016683:Supine Position