Impact of MRI-based postimplant dosimetric assessment in prostate brachytherapy using contrast-enhanced T1-weighted images

Toshio Ohashi, Tetsuo Momma, Shoji Yamashita, Katsumi Nagatsuma, Kunimitsu Kanai, Kazuhito Kitagawa, Shinichi Takahashi, Takashi Hanada, Atsunori Yorozu, Naoyuki Shigematsu

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Purpose: To compare contrast-enhanced T1-weighted (CE-T1WI) magnetic resonance imaging (MRI) with computed tomography (CT) for postimplant dosimetry and seed recognition in prostate brachytherapy. Methods and Materials: A total of 245 patients who received 125I prostate brachytherapy with or without external beam radiotherapy were enrolled. For postimplant analysis, CT and MRI scans were obtained at 1 month after seed implantation. For MRI-based dosimetry, T2-weighted images were fused with the CE-T1WI; the prostate was delineated on the T2-weighted images, and the seed detection was performed manually on the CE-T1WI. In CT-based dosimetry, the seed detection was essentially performed automatically. The dosimetric results obtained by MRI-based and CT-based dosimetry were compared. Results: The mean prostate D90 (the minimum dose received by 90% of the prostate volume) estimated by MRI-based and CT-based dosimetry were 113% and 115%, respectively, with no significant difference. The mean prostate V100 (the percent volume of the postimplant prostate receiving 100% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 95.2% and 95.8%, respectively, again with no significant difference. The mean prostate V150 (the percent volume of the postimplant prostate receiving 150% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 52.8% and 57.0%, respectively (p<0.01). In all of the 35 patients (14%) in whom the MRI-based V150 were at least 10% lower than the CT-based results, the seed detection by CT-based dosimetry was overestimated in highly seed-clustered areas or in the areas close to calcifications because of reconstruction artifacts in CT images. Conclusions: MRI-based dosimetry using CE-T1WI appears to be acceptable. Our results suggest that MRI-based dosimetry is a practical method for estimation of the higher dose distribution, especially if seeds are clustered together or when they are close to calcifications.

Original languageEnglish
Pages (from-to)468-475
Number of pages8
JournalBrachytherapy
Volume11
Issue number6
DOIs
Publication statusPublished - 2012 Nov

Keywords

  • Brachytherapy
  • Dosimetry
  • MRI
  • Postimplant
  • Prostate cancer

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging

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