ABSTRACT
Introduction: An increasing number of prostate permanent seeds implant (LDR) procedures are being performed annually for localized prostate cancer (CaP). As local intraprostatic radiotherapy, LDR needs exact volume and dose calculations before and after the implant of the radioactive sources. Post-implant dosimetric analysis is mandatory and is generally evaluated by CT. As different physicians can differ in their volume definition of the prostate gland on the same post-implant CT images, the final dosimetric quality of the implant may also vary. Material and Methods: Our purpose is to identify the degree of agreement among three professionals skilled on prostate imaging and the dosimetric consequences of any disagreement in the sets of images from 36 consecutive patients submitted to LDR as monotherapy at Hospital A.C. Camargo (São Paulo, Brazil) from February 2005 to July 2006. Results: Median reconstructed prostate volumes ranged from 20.0 cc to 70.3 cc. Student´s t-test showed significant differences in the prostate volumes among the 3 observers (p <0.001, p <0.001 and p =0.010, respectively). The Pearson´s correlation coefficient was 0.912 for prostate volumes, 0.762 for D90, 0.932 for V100 and 0.935 for V150 when all reviewers were considered. The global test revealed significant differences in D90, V100 and V150 among the reviewers (p <0.0001). Conclusion: CT-based post-implant dosimetry allow the calculation of dose delivered to the prostate and surrounding and intra-prostatic normal tissues, but this method does not provide enough information to allow observers to reproducibly delineate the prostate volume without any discordance, which impacts in the final dosimetry.