Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2012

Abstract number 5

Functional MRI guided HDR prostate brachytherapy tumour boost: a feasibility study. 

Josh Mason, Bashar Al-Qaisieh, Peter Bownes, Dan Wilson
Medical Physics, St James’s Institute of Oncology, Leeds Teaching Hospitals NHS Trust
David L. Buckley
Division of Medical Physics, University of Leeds
David Thwaites
Institute of Medical Physics, School of Physics, University of Sydney, Australia
Brendan Carey
Radiology, St James’s Institute of Oncology, Leeds Teaching Hospitals NHS Trust
Ann Henry
Clinical Oncology, St James’s Institute of Oncology, Leeds Teaching Hospitals NHS Trust

Aims/Introduction: For standard HDR prostate brachytherapy in combination with EBRT, a single 15Gy fraction is delivered to the whole prostate. In this study, the feasibility of identifying tumour regions using MRI, image registration of MRI to treatment planning trans-rectal ultrasound (TRUS) and dose optimisation to deliver increased dose to tumour regions is investigated.

Material/Methods: 15 patients underwent T2-weighted (T2W), diffusion weighted (DWI) and dynamic contrast-enhanced (DCE) MRI scans the day before HDR prostate brachytherapy treatment. For this feasibility study, all patients were analysed retrospectively. Tumour delineation was performed by a radiologist. Regions suspicious for tumour on all 3 MRI datasets were classed as gross tumour volume (GTV), regions suspicious on at least one MRI dataset were classed as clinical target volume (CTV). MRI GTV and CTVs were manually registered to treatment planning TRUS images. A margin of 3mm was applied to each CTV. Dose optimisation was investigated by comparing the dose delivered to the GTV, CTV and CTV + margin for (i) the delivered treatment plan and (ii) a modified version of the delivered plan optimising dose to the CTV.

Results: GTVs were identified in 11 patients with mean volume 0.52 cc (range 0.01 – 1.7 cc). CTVs were identified in all patients with mean volume 2.6 cc (range 0.1-23.6 cc). Though no patient had more than 1 GTV, 5 patients had more than one CTV. For the first 5 patients included in the dose optimisation study, the mean D90 increased from 20.4Gy to 29.5Gy for GTV, from 18.6Gy to 25.9Gy for CTV, and from 18Gy to 21.9Gy for CTV+margin. Urethral and rectal dose were maintained with normal constraints.

Conclusion: Functional MRI guided HDR prostate brachytherapy tumour boost is feasible. It is possible to achieve significant increased dose to tumour regions without violating urethral and rectal dose constraints.