title: Role of intra- or periprostatic calcifications in image-guided radiotherapy for prostate cancer.
abstract: OBJECTIVE
  Image-guided radiotherapy (IGRT) allows more precise localization of the prostate, thus minimizing errors resulting from organ motion and set-up during treatment of prostate cancer. Using megavoltage cone-beam computed tomography (MVCBCT), references such as bones, the prostate itself or implanted fiducial markers can be used as surrogates to correct patient positioning immediately before each treatment fraction. However, the use of fiducials requires an invasive procedure and may increase costs. We aimed to assess whether intra- or periprostatic calcifications (IPC) could be used as natural fiducials.
  
  
  METHODS
  Data on patients treated with IGRT for prostate cancer with clearly visible IPC and implanted fiducials in both planning CT and MVCBCT images were reviewed. IPC were classified as central when inside the prostate and peripheral when within the planning target volume. Daily deviations in lateral, longitudinal, and vertical directions from baseline positioning using fiducials and using IPC were compared.
  
  
  RESULTS
  A total of 287 MVCBCT images were obtained and analyzed from 10 patients. The mean ± standard deviation daily deviation (mm) in the lateral, longitudinal, and vertical coordinates were 0.55 ± 3.11, 0.58 ± 3.45, and -0.54 ± 4.03, respectively, for fiducials, and 0.72 ± 3.22, 0.63 ± 3.58, and -0.69 ± 4.26, for IPC. The p values for comparisons (fiducials vs. IPC) were 0.003, 0.653, and 0.078 for lateral, longitudinal, and vertical coordinates, respectively. When cases with central IPC were analyzed (n = 7), no significant difference was found in such comparisons. Central IPC and fiducials exhibited a similar pattern of displacement during treatment, with equal values for daily displacements in the three directions for more than 90% of measurements.
  
  
  CONCLUSIONS
  Our data suggest that centrally located IPC may be used as natural fiducials for treatment positioning during IGRT for prostate cancer, with potential reductions in the risks and costs associated with fiducial implantation.
authors.affiliation: Department of Radiotherapy, Hospital Sírio-Libanês, São Paulo, SP, Brazil. samir.hanna@hsl.org.br
authors.forename: Samir Abdallah
authors.initials: SA
authors.lastname: Hanna
authors.forename: Wellington Furtado Pimenta
authors.initials: WF
authors.lastname: Neves-Junior
authors.forename: Gustavo Nader
authors.initials: GN
authors.lastname: Marta
authors.forename: Cecília Maria Kalil
authors.initials: CM
authors.lastname: Haddad
authors.forename: João Luis Fernandes
authors.initials: JL
authors.lastname: da Silva
mesh_terms: D002114:Calcinosis / Q000000981:diagnostic imaging*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging*; D011469:Prostatic Diseases / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided; D012189:Retrospective Studies