Oral & Poster Presentation – Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2013

Abstract number 4

Dosimetry Modeling for Focal LDR Prostate Brachytherapy

Bashar Al-Qaisieh
Medical Phyiscs and Engineering, St James’s Institute of Oncology, Leeds
Josh Mason
Medical Phyiscs and Engineering, St James’s Institute of Oncology, Leeds
Ann Henry
Clinical Oncology, St James’s Institute of Oncology, Leeds
Peter Bownes
Medical Phyiscs and Engineering, St James’s Institute of Oncology, Leeds
Stephen Langley
Department of Urology, Royal Surrey County Hospital NHS Foundation Trust, Guildford

Aims/Introduction: Following the report of a consensus meeting on focal prostate brachytherapy(1), it was agreed to retrospectively model LDR treatment planning techniques, including evaluation of robustness of treatment plans against random and systematic seed movement, and measurement of inter seed attenuation (ISA).

Materials/Methods: Nine patients were selected for this study according to clinical data, template biopsy and multi parametric MRI. This data was used to contour target volumes and organs at risk. Three treatment plans were produced for each case: standard, hemi and ultra-focal as recommended by the consensus report(1).  Plans used 6711 seeds with source strength 0.5 U and prescription dose 145 Gy. Monte Carlo code was created to assess plan robustness and ISA.

Results: Hemi and focal plans use between 30% and 70% less seeds and needles compared to standard plans. Prostate D90 increased by 19% and 69%, urethra D10 decreased by 7% and 55%, and rectal D2cc decreased by 28% and 60%, for hemi and ultra focal plans respectively.  From plan robustness analysis, a random shift in seed position with SD=4mm would result in V100 and D90 dropping by 7.2% and 14% respectively for standard plans, 7.3% and 20% for hemi plans and 5% and 32% for ultra focal plans.  ISA has similar effect on DVH parameters for hemi and ultra focal plans as for standard plans.

Conclusions: Treatment planning for hemi and ultra-focal options is feasible. Dose constrains are easily met with a notable reduction to organs at risk. Treating focal targets makes seed positioning more critical. 

Additional co-authors: Louise Dickinson, Ahmed Hashim, Mark Emberton (all Division of Surgery and Interventional Science, University College London, UK).

The authors would also like to acknowledge the following: Peter Grimm, Ferran Guedea, David Bostwick, Francisco Gómez Veiga, Stephan Machtens.

(1)        Langley S, et al. BJU Int. 2012 Feb;109 Suppl 1:7-16.