title: Dosimetric evaluation of three adaptive strategies for prostate cancer treatment including pelvic lymph nodes irradiation.
abstract: OBJECTIVE
  The movements of the prostate relative to the pelvic lymph nodes during intensity-modulated radiation therapy treatment can limit margin reduction and affect the protection of the organs at risk (OAR). In this study, the authors performed an analysis of three adaptive treatment strategies that combine information from both bony and gold marker registrations. The robustness of those treatments against the interfraction prostate movements was evaluated.
  
  
  METHODS
  A retrospective study was conducted on five prostate cancer patients with 7-13 daily cone-beam CTs (CBCTs). The clinical target volumes (CTVs) consisting of pelvic lymph nodes, prostate, and seminal vesicles as well as the OARs were delineated on each CBCT and the initial CT. Three adaptive strategies were analyzed. Two of these methods relied on a two-step patient positioning at each fraction. First step: a bony registration was used to deliver the nodal CTV prescription. Second step: a gold marker registration was then used either to (1) complete the dose delivered to the prostate (complement); (2) or give almost the entire prescription to the prostate with a weak dose gradient between the targets to compensate for possible motions (gradient). The third method (COR) used a pool of precalculated plans based on images acquired at previous treatment fractions. At each new fraction, a plan is selected from that pool based on the daily position of prostate center-of-mass. The dosimetric comparison was conducted and results are presented with and without the systematic shift in the prostate position on the CT planning. The adaptive strategies were compared to the current clinical standard where all fractions are treated with the initial nonadaptive plan.
  
  
  RESULTS
  The minimum daily prostate D95% is improved by 2%, 9%, and 6% for the complement, the gradient, and the COR approaches, respectively, compared to the nonadaptive method. The average nodal CTV D95% remains constant across the strategies, except for the gradient approach where a reduction of 7% is observed. However, a correction of the systematic shift reduced the problem, and the adaptive strategies remain robust against the prostate movement across the fraction. The bladder V55Gy is reduced by 35% on average for the adaptive strategies.
  
  
  CONCLUSIONS
  Because they offer increased CTV coverage and OAR sparing, adaptive methods may be suitable candidates for simple and efficient adaptive treatment strategies for prostate cancer. Margin reduction and systematic error correction in the prostate position improve the protection of the OAR and the dose coverage. A cumulative dose to simulate a complete treatment would show real effects and allow a better comparison between each method.
authors.affiliation: Département de Physique, de génie Physique et d'optique et Centre de Recherche sur le Cancer, Université Laval, Québec, Québec G1V 0A6, Canada and Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada.
authors.forename: Audrey
authors.initials: A
authors.lastname: Cantin
authors.affiliation: Département de Physique, de génie Physique et d'optique et Centre de Recherche sur le Cancer, Université Laval, Québec, Québec G1V 0A6, Canada and Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada.
authors.forename: Luc
authors.initials: L
authors.lastname: Gingras
authors.affiliation: Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada.
authors.forename: Bernard
authors.initials: B
authors.lastname: Lachance
authors.affiliation: Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada.
authors.forename: William
authors.initials: W
authors.lastname: Foster
authors.affiliation: Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada and Département de Radio-Oncologie, CSSS de Gatineau-Hôpital de Gatineau, 909 Boulevard La Vérendrye, Gatineau, Québec J8P 7H2, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Goudreault
authors.affiliation: Département de Physique, de génie Physique et d'optique et Centre de Recherche sur le Cancer, Université Laval, Québec, Québec G1V 0A6, Canada and Département de Radio-Oncologie et Centre de Recherche du CHU de Québec, CHU de Québec-Université Laval, 11 côte du Palais, Québec, Québec G1R 2J6, Canada.
authors.forename: Louis
authors.initials: L
authors.lastname: Archambault
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods; D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008198:Lymph Nodes / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008297:Male; D056888:Patient Positioning; D010388:Pelvis / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D012669:Seminal Vesicles / Q000000981:diagnostic imaging / Q000528:radiation effects
chemical_list: D006046:Gold