[Intraprostatic calcifications as natural fiducial markers in image-guided radiotherapy for prostate cancer]

To establish whether intraprostatic calcifications can serve as natural fiducials for image-guided radiotherapy (IGRT), replacing the implantation of intraprostatic fiducial markers.

Patients with prostate cancer, having intraprostatic calcifications visible on CT scan were selected and underwent intensity-modulated radiotherapy/3D conformal radiotherapy with IGRT in the department of radiotherapy of Henri-Mondor Hospital. All cone-beam computed tomographies (CBCT) were repositioned on intraprostatic calcifications. For each acquired image, displacements of intraprostatic calcifications were calculated with reference to position on planning CT in three directions: lateral, longitudinal and vertical.

Between 2011 and 2013, nine patients had 183 CBCT. For each image, three displacements and space coordinates were calculated using a single reference (intraprostatic calcification). Mean lateral, longitudinal and vertical movements were 0.26±5.7 mm, -1±4.6 mm and 0.42±3.5 mm, respectively.

Studies exploring prostatic movements with fiducial markers as reference and ours with natural fiducials yield similar results. Our data confirm previous studies that have suggested that intraprostatic calcifications can be used as natural fiducials with potential reduction of iatrogenic risks and costs associated with the implantation of fiducial markers.