Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2011

Abstract number 6

Assessing the benefit of utilising higher activity seeds in larger prostate volumes

Wood D, Specialised Brachytherapy Radiographer, The Christie Hospital, Manchester
Morrissey N, Specialised Brachytherapy Radiographer, The Christie Hospital, Manchester
Logue J, Clinical Director, Clinical Oncology, The Christie Hospital, Manchester
Wylie J, Consultant, Clinical Oncology, The Christie Hospital, Manchester
Elliot PA, Consultant, Clinical Oncology, The Christie Hospital, Manchester

Introduction: The incidence of acute urinary morbidity following brachytherapy is higher with larger prostate volumes.  Although multi-factorial it is associated with the number of needles inserted (1) and the localised trauma of peri-urethral needle insertion and manipulation (2).  Our standard practise is to utilise a seed activity between 0.356-0.3609 mCi irrespective of pre-planned prostatic volume.  Although satisfactory for prostate volumes <50cc, to achieve acceptable dose distribution for prostates >50cc a much larger number of seeds and needles are required with the potential for heightened urinary morbidity.  We therefore explored the degree of needle sparing achieved when using a commonly available higher activity seed of 0.536 mCi in prostates >50cc.

Methods: Twenty patients with trans-rectal ultrasound measured prostate volumes between 50-69cc were retrospectively re-planned and checked by two independent radiographers using the increased activity I-125 seed. Patients were chosen based on chronological order of referral for prostate brachytherapy.  Needle number and prostate V100, V150, V200, rectal d100 and urethral d150 were specified and recorded as per current departmental protocol and compared against the actual delivered plan using our standard seed activity.

Results: By utilising the higher activity seed the mean needle number was reduced by 25% with no adverse effects on prostate V100, V150 and V200. Mean needle number was 32 with 0.356-0.369mCi seeds (range 26-35) compared to 24 with 0.536mCi (range 22-29).  The mean prostate V100 was 99.74% with 0.536mCi seeds compared to 99.56% with 0.356-0.369mCi seeds.  Urethral and rectal doses were slightly increased with higher activity seeds but remained within departmental limits.

Conclusions: Increasing seed activity to 0.536mCi resulted in far fewer needles being required to deliver the required PTV dose without exceeding dose constraints.  This simple manoeuvre may help reduce urinary morbidity when treating larger prostates. 

References
1) Lee N,et al; Int.J RadOncBioPhys2000 Dec1 485),1457-60
2) Eapen et al;RadOncBioPhysics2004 (0360-0316)59:51392-94