title: Practical method of adaptive radiotherapy for prostate cancer using real-time electromagnetic tracking.
abstract: OBJECTIVE
  We have created an automated process using real-time tracking data to evaluate the adequacy of planning target volume (PTV) margins in prostate cancer, allowing a process of adaptive radiotherapy with minimal physician workload. We present an analysis of PTV adequacy and a proposed adaptive process.
  
  
  METHODS
  Tracking data were analyzed for 15 patients who underwent step-and-shoot multi-leaf collimation (SMLC) intensity-modulated radiation therapy (IMRT) with uniform 5-mm PTV margins for prostate cancer using the Calypso® Localization System. Additional plans were generated with 0- and 3-mm margins. A custom software application using the planned dose distribution and structure location from computed tomography (CT) simulation was developed to evaluate the dosimetric impact to the target due to motion. The dose delivered to the prostate was calculated for the initial three, five, and 10 fractions, and for the entire treatment. Treatment was accepted as adequate if the minimum delivered prostate dose (D(min)) was at least 98% of the planned D(min).
  
  
  RESULTS
  For 0-, 3-, and 5-mm PTV margins, adequate treatment was obtained in 3 of 15, 12 of 15, and 15 of 15 patients, and the delivered D(min) ranged from 78% to 99%, 96% to 100%, and 99% to 100% of the planned D(min). Changes in D(min) did not correlate with magnitude of prostate motion. Treatment adequacy during the first 10 fractions predicted sufficient dose delivery for the entire treatment for all patients and margins.
  
  
  CONCLUSIONS
  Our adaptive process successfully used real-time tracking data to predict the need for PTV modifications, without the added burden of physician contouring and image analysis. Our methods are applicable to other uses of real-time tracking, including hypofractionated treatment.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Olsen
authors.forename: Camille E
authors.initials: CE
authors.lastname: Noel
authors.forename: Kenneth
authors.initials: K
authors.lastname: Baker
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Santanam
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Michalski
authors.forename: Parag J
authors.initials: PJ
authors.lastname: Parikh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003199:Computer Systems; D019583:Dose Fractionation, Radiation; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009068:Movement; D058958:Organs at Risk / Q000528:radiation effects; D011467:Prostate / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000033:anatomy & histology / Q000528:radiation effects; D012399:Rotation; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden