Poster Presentation – Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2013

Abstract number 8

Cone Beam vs. Conventional CT in I125 Prostate Brachytherapy

Patrick Leydon
The Galway Clinic
Peter Woulfe
The Galway Clinic

Aims/Introduction: Transperineal interstitial implantation of radioactive I125 seeds is a technique which utilises three-dimensional image-based treatment planning and real-time visualization of needle insertion and seed deposition. Considerable emphasis is placed on 3D conformal dosimetric planning and precise seed placement.

Seed placement and dosimetry are verified using a CT scan between 0 to 30 days post implant, ideally within 24 hours of implantation with a catheter in situ. This allows for much more accurate contouring of the urethra and thus more accurate dose analysis is possible. The aim of this project was to examine the viability of using fluoroscopy based Cone Beam CT in theatre as a possible imaging alternative to conventional CT imaging to acquire a day 0 scan.

Materials/Methods: A quantitative and qualitative comparison of image quality between Cone Beam CT images from the Philips Allura Xper FD 20 and regular axial CT images from the Philips Gemini 16 slice CT scanner was performed. The phantoms used for assessment of image quality were the CatPhan 600 and the Siemens EMMA Phantom. The programs IQWorks and ImageJ were also used for image analysis. A comparison of dosimetry results was performed using Varian™s Variseed software and a Rando phantom implanted with several dummy seeds.

Results: Generally cone beam CT performed well against conventional CT. CatPhan test results for resolution and geometric accuracy were excellent. The main areas where conventional CT outperformed Cone Beam CT were uniformity and low contrast resolution. Dosimetry results between the two modalities show some differences, most notably D90 values, but there is good agreement overall.

Conclusions: Initial results suggest that real-time patient imaging with Cone Beam CT may be a feasible alternative to the current practice of conventional CT scanning. However this study’s sole reliance on phantoms does limit the clinically relevant conclusions which may be drawn.