Accuracy of applicator tip reconstruction in MRI-guided interstitial 192Ir-high-dose-rate brachytherapy of liver tumors

Radiother Oncol. 2015 Apr;115(1):72-7. doi: 10.1016/j.radonc.2015.01.018. Epub 2015 Mar 13.

Abstract

Background and purpose: To evaluate the reconstruction accuracy of brachytherapy (BT) applicators tips in vitro and in vivo in MRI-guided (192)Ir-high-dose-rate (HDR)-BT of inoperable liver tumors.

Materials and methods: Reconstruction accuracy of plastic BT applicators, visualized by nitinol inserts, was assessed in MRI phantom measurements and in MRI (192)Ir-HDR-BT treatment planning datasets of 45 patients employing CT co-registration and vector decomposition. Conspicuity, short-term dislocation, and reconstruction errors were assessed in the clinical data. The clinical effect of applicator reconstruction accuracy was determined in follow-up MRI data.

Results: Applicator reconstruction accuracy was 1.6±0.5 mm in the phantom measurements. In the clinical MRI datasets applicator conspicuity was rated good/optimal in ⩾72% of cases. 16/129 applicators showed not time dependent deviation in between MRI/CT acquisition (p>0.1). Reconstruction accuracy was 5.5±2.8 mm, and the average image co-registration error was 3.1±0.9 mm. Vector decomposition revealed no preferred direction of reconstruction errors. In the follow-up data deviation of planned dose distribution and irradiation effect was 6.9±3.3 mm matching the mean co-registration error (6.5±2.5 mm; p>0.1).

Conclusion: Applicator reconstruction accuracy in vitro conforms to AAPM TG 56 standard. Nitinol-inserts are feasible for applicator visualization and yield good conspicuity in MRI treatment planning data. No preferred direction of reconstruction errors were found in vivo.

Keywords: Applicator reconstruction accuracy; Image registration; Interstitial (192)Ir-high-dose-rate brachytherapy; Liver tumors; MRI-based treatment planning; MRI-guided intervention.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Brachytherapy / methods*
  • Female
  • Humans
  • Iridium Radioisotopes / therapeutic use
  • Liver Neoplasms / radiotherapy*
  • Magnetic Resonance Imaging / methods
  • Male
  • Middle Aged
  • Phantoms, Imaging
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods

Substances

  • Iridium Radioisotopes