Dosimetric impact of contouring and needle reconstruction uncertainties in US-, CT- and MRI-based high-dose-rate prostate brachytherapy treatment planning

Radiother Oncol. 2017 Apr;123(1):125-132. doi: 10.1016/j.radonc.2017.01.007. Epub 2017 Mar 8.

Abstract

Background and purpose: The purpose was to evaluate the dosimetric impact of target contouring and needle reconstruction uncertainties in an US-, CT- and MRI-based HDR prostate BT treatment planning.

Material and methods: US, CT, and MR images were acquired post-needle insertion in 22 HDR-BT procedures for 11 consecutive patients. Dose plans were simulated for an US-, CT- and MRI-based HDR-BT treatment planning procedure. Planning uncertainties in US- and CT-based plans were evaluated using MRI-based planning as reference. Target (CTVProstate) was re-contoured on MRI. Dose results were expressed in total equivalent dose given in 2Gy fractionation dose for EBRT (46Gy) plus 2 HDR-BT fractions.

Results: Uncertainties in US- and CT-based planning caused the planned CTVProstate-D90% to decrease with a mean of 2.9±5.0Gy (p=0.03) and 2.9±2.9Gy (p=0.001), respectively. The intra-observer contouring variation on MRI resulted in a mean variation of 1.6±1.5Gy in CTVProstate-D90%. Reconstruction uncertainties on US resulted in a dose variation of±3Gy to the urethra, whereas data for CT were not available for this.

Conclusions: Uncertainties related to contouring and reconstruction in US- and CT-based HDR-BT treatment plans resulted in a systematic overestimation of the prescribed target dose. Inter-modality uncertainties (US and CT versus MR) were larger than MR intra-observer uncertainties.

Keywords: CT-based brachytherapy; High-dose-rate prostate brachytherapy; Intra observer contouring variability; MRI-based brachytherapy; Prostate brachytherapy; US-based brachytherapy.

MeSH terms

  • Brachytherapy / methods*
  • Dose Fractionation, Radiation
  • Humans
  • Magnetic Resonance Imaging / methods
  • Male
  • Prostatic Neoplasms / diagnostic imaging
  • Prostatic Neoplasms / radiotherapy*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Tomography, X-Ray Computed / methods
  • Ultrasonography / methods
  • Uncertainty