A comparative study of seed localization and dose calculation on pre- and post-implantation ultrasound and CT images for low-dose-rate prostate brachytherapy

Abstract

This work investigates variation in the volume of the prostate measured at different stages through the prostate brachytherapy procedure for 30 patients treated with I-125 radioactive seeds. The implanted seeds were localized on post-implantation ultrasound (US) images and the effect of prostate enlargement due to edema on dose coverage for 15 patients was studied. The volume of the prostate was measured at four stages as follows: (a) 2-3 weeks prior to implantation using US imaging, (b) then at the start of the intra-operative prostate brachytherapy procedure on the day of the implant, (c) immediately post-implantation using US imaging in the operating room and (d) finally by CT imaging at nearly 4 weeks post-implantation. Comparative prostate volume studies were performed using US imaging stepper and twister modes. For the purpose of this study, the implanted seeds were localized successfully on post-implant ultrasound twister images, retrospectively. The plans using post-implant US imaging were compared with intra-operative plans on US and plans created on CT images. The prostate volume increases about 10 cm(3) on average due to edema induced by needle insertion and seed loading during implantation. The visibility of the implanted seeds on US twister images acquired post-implantation is as good as those on CT images and can be localized and used for dose calculation. The dose coverage represented by parameters such as D90 (dose covering 90% of the volume) and V100 (volume covered by 100% dose) is poorer on plans performed on post-implantation twister US studies than on the intra-operative live plan or the CT scan performed 4 weeks post-operatively. For example, the mean D90 difference on post-implantation US is lower by more than 15% than that on pre-implantation US. The volume enlargement of the prostate due to edema induced by needle insertion and seed placement has a significant effect on the quality of dosimetric coverage in brachytherapy prostate seed implants. Here, we introduced a new approach based on the use of post-implant US twister images to correct for prostate enlargement intra-operatively. Besides the ability to localize the seeds and superior soft tissue visibility, the twister US images include effects of the enlargement of the prostate gland and seed migration during the implantation procedure.

The results of real‐time brachytherapy for the management of low‐ and intermediate‐risk prostate cancer in patients with prostate volumes up to 100 mL

“…This fear of pubic arch interference may result in needles being placed more centrally in the gland, increasing the urethral dose and potential toxicity [6]. As a consequence of these limitations there is a reduced correlation between the dosimetry of the plan and the dose delivered [16–18].…”

Quantifying the effect of seed orientation in postplanning dosimetry of low‐dose‐rate prostate brachytherapy

“…The American Association of Physicists in Medicine (AAPM), the American Brachytherapy Society (ABS), and the European Society for Radiotherapy and Oncology (ESTRO) [2][3][4] recommend that postimplant dosimetry, related to the treatment quality, should be performed on every patient undergoing PPB. Previous studies [5][6][7] have shown that the actual implant technique may lead to differences in the position and orientation of the seeds between the treatment plan and the post-treatment dosimetry, potentially influencing the treatment quality. The seed misplacement problem has been investigated and categorized, [8][9][10] but the seed orientation problem has yet to be precisely studied.…”

Comparison of Prostate Contours between Conventional Stepping Transverse Imaging and Twister Based Sagittal Imaging in Permanent Interstitial Prostate Brachytherapy

“…We aim to conduct further study to quantify prostate rotation due to the TRUS probe. With regard to prostate volume, a report by Ali et al also compared transverse and sagittal image acquisitions [10]. They reported that in a group of patients with a small prostate size, the prostate volume in the sagittal image acquisitions was larger than that in the transverse image acquisitions, although the opposite result was shown in the large (> 50 cc) prostate group.…”