title: Offline multiple adaptive planning strategy for concurrent irradiation of the prostate and pelvic lymph nodes.
abstract: OBJECTIVE
  Concurrent irradiation of the prostate and pelvic lymph nodes (PLNs) can be challenging due to the independent motion of the two target volumes. To address this challenge, the authors have proposed a strategy referred to as Multiple Adaptive Planning (MAP). To minimize the number of MAP plans, the authors' previous work only considered the prostate motion in one major direction. After analyzing the pattern of the prostate motion, the authors investigated a practical number of intensity-modulated radiotherapy (IMRT) plans needed to accommodate the prostate motion in two major directions simultaneously.
  
  
  METHODS
  Six patients, who received concurrent irradiation of the prostate and PLNs, were selected for this study. Nine MAP-IMRT plans were created for each patient with nine prostate contours that represented the prostate at nine locations with respect to the PLNs, including the original prostate contour and eight contours shifted either 5 mm in a single anterior-posterior (A-P), or superior-inferior (S-I) direction, or 5 mm in both A-P and S-I directions simultaneously. From archived megavoltage cone beam CT (MV-CBCT) and a dual imaging registration, 17 MV-CBCTs from 33 available MV-CBCT from these patients showed large prostate displacements (>3 mm in any direction) with respect to the pelvic bones. For each of these 17 fractions, one of nine MAP-IMRT plans was retrospectively selected and applied to the MV-CBCT for dose calculation. For comparison, a simulated isocenter-shifting plan and a reoptimized plan were also created for each of these 17 fractions. The doses to 95% (D95) of the prostate and PLNs, and the doses to 5% (D5) of the rectum and bladder were calculated and analyzed.
  
  
  RESULTS
  For the prostate, D95 > 97% of the prescription dose was observed in 16, 16, and 17 of 17 fractions for the MAP, isocenter-shifted, and reoptimized plans, respectively. For PLNs, D95 > 97% of the prescription doses was observed in 10, 3, and 17 of 17 fractions for the three types of verification plans, respectively. The D5 (mean ± SD) of the rectum was 45.78 ± 5.75, 45.44 ± 4.64, and 44.64 ± 2.71 Gy, and the D5 (mean ± SD) of the bladder was 45.18 ± 2.70, 46.91 ± 3.04, and 45.67 ± 3.61 Gy for three types of verification plans, respectively.
  
  
  CONCLUSIONS
  The MAP strategy with nine IMRT plans to accommodate the prostate motions in two major directions achieved good dose coverage to the prostate and PLNs. The MAP approach can be immediately used in clinical practice without requiring extra hardware and software.
authors: Department of Radiation Oncology, Cleveland Clinic, Cleveland, Ohio 44195.
authors: Peng
authors: P
authors: Qi
authors: Department of Radiation Oncology, University of California-San Francisco, San Francisco, California 94143.
authors: Jean
authors: J
authors: Pouliot
authors: Department of Radiation Oncology, University of California-San Francisco, San Francisco, California 94143.
authors: Mack
authors: M
authors: Roach
authors: Department of Radiation Oncology, Cleveland Clinic, Cleveland, Ohio 44195.
authors: Ping
authors: P
authors: Xia
mesh_terms: D054893:Cone-Beam Computed Tomography; D006801:Humans; D008198:Lymph Nodes / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008297:Male; D009068:Movement; D010388:Pelvis; D011467:Prostate / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013997:Time Factors